- Introduction
- cef table consistency-check through clear pxf
- ip cache-invalidate-delay through monitor event-trace cef ipv6 (global)
- show adjacency through show ip cef with source
- show ip mds forwarding through show monitor event-trace merged-list
- show pxf accounting through test cef table consistency
- ip cache-invalidate-delay
- ip cef
- ip cef accounting
- ip cef linecard ipc memory
- ip cef load-sharing algorithm
- ip c ef optimize neighbor resolution
- ip cef table adjacency-prefix
- ip cef table adjacency-prefix
- ip cef table consistency-check
- ip cef table event-log
- ip cef table resolution-timer
- ip cef traffic-statistics
- ip load-sharing
- ip route -cache
- ip route-cache policy
- ip v erify unicast notification threshold
- ip verify unicast r eve rse-p ath
- ip v erify unicast source reachable-via
- ip v erify unicast vrf
- ipv6 cef
- ipv6 cef accounting
- ipv6 cef distributed
- ipv6 cef load-sharing algorit hm
- ipv 6 cef optimize neighbor resolution
- ipv6 verify unicast reverse-path
- ipv6 verify unicast source reachable-via
- mls cef maximum-routes
- mls cef tunnel fragment
- mls erm priority
- mls ip
- mls ip cef a ccounting per-prefix
- mls ip cef load-sharing
- mls ip cef rate-limit
- mls ip cef rpf hw-enable-rpf-acl
- mls ip cef rpf interface-group
- mls ip cef rpf multipath
- mon itor elog trigger position
- monitor event-trace (EXEC)
- monitor event-trace (global)
- mon itor event-trace cef (EXEC)
- mo nitor event-trace cef (global)
- mo nitor event-trace cef ipv4 (global)
- mon itor event-trace cef ipv6 (global)
ip cache-invalidate-delay
To control the invalidation rate of the IP route cache, use the ip cache-invalidate-delay command in global configuration mode. To allow the IP route cache to be immediately invalidated, use the no form of this command.
ip cache-invalidate-delay [ minimum maximum quiet threshold ]
Syntax Description
Command Default
The invalidation rate of the IP route cache is not controlled.
Command Modes
Command History
Usage Guidelines
After you enter the ip cache-invalidate-delay command all cache invalidation requests are honored immediately.
The IP fast-switching and autonomous-switching features maintain a cache of IP routes for rapid access. When a packet is to be forwarded and the corresponding route is not present in the cache, the packet is process switched and a new cache entry is built. However, when routing table changes occur (such as when a link or an interface goes down), the route cache must be flushed so that it can be rebuilt with up-to-date routing information.
This command controls how the route cache is flushed. The intent is to delay invalidation of the cache until after routing has settled down. Because route table changes tend to be clustered in a short period of time, and the cache may be flushed repeatedly, a high CPU load might be placed on the router.
When this feature is enabled, and the system requests that the route cache be flushed, the request is held for at least minimum seconds. Then the system determines whether the cache has been “quiet” (that is, less than threshold invalidation requests in the last quiet seconds). If the cache has been quiet, the cache is then flushed. If the cache does not become quiet within maximum seconds after the first request, it is flushed unconditionally.
Manipulation of these parameters trades off CPU utilization versus route convergence time. Timing of the routing protocols is not affected, but removal of stale cache entries is affected.
Examples
The following example shows how to set a minimum delay of 5 seconds, a maximum delay of 30 seconds, and a quiet threshold of no more than 5 invalidation requests in the previous 10 seconds:
Related Commands
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ip cef
To enable Cisco Express Forwarding on the route processor card, use the ip cef command in global configuration mode. To disable Cisco Express Forwarding, use the no form of this command.
Cisco IAD2420 Series Routers, Cisco 2600 Series Routers, Cisco 3600 Series Routers, Cisco 3700 Series Routers, Cisco 7200 Series Routers
Cisco ASR 1000 Series Aggregation Services Routers
Syntax Description
(Optional) Enables distributed Cisco Express Forwarding operation. Distributes Cisco Express Forwarding information to line cards. Line cards perform express forwarding. |
Command Default
Cisco Express Forwarding is enabled by default on most platforms. To find out if Cisco Express Forwarding is enabled by default on your platform, enter the show ip cef command.
Command Modes
Command History
Usage Guidelines
The ip cef command is not available on the Cisco 12000 series because that router series operates only in distributed Cisco Express Forwarding mode. Distributed Cisco Express Forwarding is enabled also on the Cisco 6500 series router.
Cisco Express Forwarding is advanced Layer 3 IP switching technology. Cisco Express Forwarding optimizes network performance and scalability for networks with dynamic, topologically dispersed traffic patterns, such as those associated with web-based applications and interactive sessions.
If you enable Cisco Express Forwarding and then create an access list that uses the log keyword, the packets that match the access list are not Cisco Express Forwarding switched. They are fast switched. Logging disables Cisco Express Forwarding.
The following example shows how to enable standard Cisco Express Forwarding operation:
The following example shows how to enable distributed Cisco Express Forwarding operation:
Related Commands
ip cef accounting
To enable Cisco Express Forwarding network accounting, use the ip cef accounting command in global configuration mode or interface configuration mode. To disable network accounting of Cisco Express Forwarding, use the no form of this command.
ip cef accounting accounting-types
no ip cef accounting accounting-types
Specific Cisco Express Forwarding Accounting Information Through Interface Configuration Mode
ip cef accounting non-recursive { external | internal }
no ip cef accounting non-recursive { external | internal }
Syntax Description
Command Default
Command Modes
Global configuration (config)
Interface configuration (config-if)
Command History
Usage Guidelines
Collecting statistics can help you better understand Cisco Express Forwarding patterns in your network.
When you enable network accounting for Cisco Express Forwarding from global configuration mode, accounting information is collected at the Route Processor (RP) when Cisco Express Forwarding mode is enabled and at the line cards when distributed Cisco Express Forwarding mode is enabled. You can then display the collected accounting information using the show ip cef privileged EXEC command.
For prefixes with directly connected next hops, the non-recursive keyword enables express forwarding of the collection of packets and bytes through a prefix. This keyword is optional when this command is used in global configuration mode.
This command in interface configuration mode must be used in conjunction with the global configuration command. The interface configuration command allows a user to specify two different bins (internal or external) for the accumulation of statistics. The internal bin is used by default. The statistics are displayed through the show ip cef detail command.
Per-destination load balancing uses a series of 16 hash buckets into which the set of available paths are distributed. A hash function operating on certain properties of the packet is applied to select a bucket that contains a path to use. The source and destination IP addresses are the properties used to select the bucket for per-destination load balancing. Use the load-balance-hash keyword with the ip cef accounting command to enable per-hash-bucket counters. Enter the show ip cef prefix internal command to display the per-hash-bucket counters.
Note The ip cef accounting command is not supported on the Cisco 7600 series router.
Examples
The following example shows how to enable the collection of Cisco Express Forwarding accounting information for prefixes directly connected to the next hops:
Related Commands
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Enables Cisco Express Forwarding for IPv6 (CEFv6) and distributed CEFv6 (dCEFv6) network accounting. |
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Displays information about packets forwarded by Cisco Express Forwarding. |
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ip cef linecard ipc memory
To configure the line card memory pool for the Cisco Express Forwarding queuing messages, use the ip cef linecard ipc memory command in global configuration mode. To return to the default Inter-process Communications (IPC) memory allocation, use the no form of this command.
ip cef linecard ipc memory kbps
no ip cef linecard ipc memory kbps
Syntax Description
Kilobytes of line card memory allocated. Range is 0 to 12800. The default IPC memory allocation is 25 messages. However, this value depends on the switching platform. |
Command Default
If you do not configure a line card memory pool for the Cisco Express Forwarding queuing messages, the default is the IPC memory allocation for the switching platform.
Command Modes
Command History
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Usage Guidelines
This command is available only on distributed switching platforms.
If you are expecting large routing updates to the Route Processor (RP), use this command to allocate a larger memory pool on the line cards for queuing Cisco Express Forwarding routing update messages. The memory pool reduces the transient memory requirements on the RP.
To display and monitor the current size of the Cisco Express Forwarding message queues, use the show cef linecar d command. Also, the peak size is recorded and displayed when you use the detail keyword.
Examples
The following example shows how to configure the Cisco Express Forwarding line card memory queue to 128000 kilobytes per second:
Related Commands
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Displays detailed Cisco Express Forwarding information for the specified line card. |
ip cef load-sharing algorithm
To select a Cisco Express Forwarding load-balancing algorithm, use the ip cef load-sharing algorithm command in global configuration mode. To return to the default universal load-balancing algorithm, use the no form of this command.
ip cef load-sharing algorithm { original | tunnel [ id ] | universal [ id ] | include-ports { source [ id ] | [ destination ] [ id ] | source [ id ] destination [ id ]}}
no ip cef load-sharing algorithm
Syntax Description
Command Default
The universal load-balancing algorithm is selected. If you do not configure the fixed identifier for a load-balancing algorithm, the router automatically generates a unique ID.
Command Modes
Command History
Usage Guidelines
The original Cisco Express Forwarding load-balancing algorithm produced distortions in load sharing across multiple routers because of the use of the same algorithm on every router. When the load-balancing algorithm is set to universal mode, each router on the network can make a different load sharing decision for each source-destination address pair, and that resolves load-balancing distortions.
The tunnel algorithm is designed to share the load more fairly when only a few source-destination pairs are involved.
The include-ports algorithm allows you to use the Layer 4 source and destination ports as part of the load-balancing decision. This method benefits traffic streams running over equal-cost paths that are not loadshared because the majority of the traffic is between peer addresses that use different port numbers, such as Real-Time Protocol (RTP) streams. The include-ports algorithm is available in Cisco IOS Release 12.4(11)T and later releases.
Examples
The following example shows how to enable the Cisco Express Forwarding load-balancing algorithm for tunnel environments:
Related Commands
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Records Cisco Express Forwarding load-balancing hash algorithm events |
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ip cef optimize neighbor resolution
To configure address resolution optimization from Cisco Express Forwarding for IPv4 for directly connected neighbors, use the ip cef optimize neighbor resolution command in global configuration mode. To disable address resolution optimization from Cisco Express Forwarding for directly connected neighbors, use the no form of this command.
ip cef optimize neighbor resolution
no ip cef optimize neighbor resolution
Syntax Description
Command Default
If this command is not configured, Cisco Express Forwarding does not optimize the address resolution of directly connected neighbors for IPv4.
Command Modes
Command History
Usage Guidelines
The ip cef optimize neighbor resolution command is very similar to the ipv6 cef optimize neighbor resolution command, except that it is IPv4-specific.
Use this command to trigger Layer 2 address resolution of neighbors directly from Cisco Express Forwarding for IPv4.
Examples
The following example shows how to optimize address resolution from Cisco Express Forwarding for directly connected neighbors:
Related Commands
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Configures address resolution optimization from Cisco Express Forwarding for IPv6 for directly connected neighbors. |
ip cef table adjacency-prefix
To modify how Cisco Express Forwarding adjacency prefixes are managed, use the ip cef table adjacency-prefix command in global configuration mode. To disable Cisco Express Forwarding adjacency prefix management, use the no form of this command.
ip cef table adjacency-prefix [ override | validate ]
no ip cef table adjacency-prefix [ override | validate ]
Syntax Description
(Optional) Enables Cisco Express Forwarding adjacency prefixes to override static host glean routes. |
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(Optional) Enables the periodic validation of Cisco Express Forwarding adjacency prefixes. |
Defaults
All Cisco Express Forwarding adjacency prefix management is disabled by default.
Command Modes
Command History
Usage Guidelines
When Cisco Express Forwarding is configured, the forwarding information base (FIB) table may conflict with static host routes that are specified in terms of an output interface or created by a Layer 2 address resolution protocols such as Address Resolution Protocol (ARP), map lists, and so on.
The Layer 2 address resolution protocol adds adjacencies to Cisco Express Forwarding, which in turn creates a corresponding host route entry in the FIB table. This entry is called an adjacency prefix.
If the Cisco Express Forwarding adjacency prefix entries are also configured by a static host route, a conflict occurs.
This command ensures that adjacency prefixes can override static host glean routes, and correctly restore routes when the adjacency prefix is deleted.
When you add a /31 netmask route, the new netmask does not overwrite an existing /32 Cisco Express Forwarding entry. This problem is resolved by configuring the validate keyword to periodically validate prefixes derived from adjacencies in the FIB against prefixes originating from the RIB.
Examples
The following example shows how to enable Cisco Express Forwarding table adjacency prefix override:
The following example shows how to enable Cisco Express Forwarding table adjacency prefix validation:
ip cef table adjacency-prefix
The override keyword for the ip cef table adjacency-prefix command is no longer documented as a separate command.
The information for using the override keyword for the ip cef table adjacency-prefix command has been incorporated into the ip cef table adjacency-prefix command documentation. See the ip cef table adjacency-prefix command documentation for more information.
ip cef table consistency-check
Note Effective with Cisco IOS Release 12.4(20)T, the ip cef table consistency-check command is not available in Cisco IOS software.
To enable consistency checker types and parameters for Cisco Express Forwarding tables, use the ip cef table consistency-check command in global configuration mode. To disable consistency checkers, use the no form of this command.
ip cef table consistency-check [ type { lc-detect | scan-lc | scan-rib | scan-rp }] [ count count-number ] [ period seconds ]
no ip cef table consistency-check [ type { lc-detect | scan-lc | scan-rib | scan-rp }] [ count count-number ] [ period seconds ]
Suppressing Errors During Route Updates
ip cef table consistency-check [ settle-time seconds ]
no ip cef table consistency-check [ settle-time seconds ]
Syntax Description
Command Default
Command Modes
Command History
Usage Guidelines
This command configures Cisco Express Forwarding table consistency checkers and parameters for the detection mechanism types that are listed in Table 2 .
Examples
The following example shows how to enable the Cisco Express Forwarding consistency checkers:
Related Commands,
ip cef table event-log
Note The ip cef table event-log command is not available in Cisco IOS Releases 12.2(25)S, 12.2(28)SB, 12.2(33)SRA, 12.2(33)SXH, 12.4(20)T, and later releases.
To control Cisco Express Forwarding table event-log characteristics, use the ip cef table event-log command in global configuration mode.
ip cef table event-log [ size event-number ] [ match ip-prefix mask ]
no ip cef table event-log [ size event-number ] [ match ip-prefix mask ]
Specific to Virtual Private Network (VPN) Event Log
ip cef table event-log [ size event-number ] [ vrf vrf-name ] [ match ip-prefix mask ]
no ip cef table event-log [ size event-number ] [ vrf vrf-name ] [ match ip-prefix mask ]
Syntax Description
Defaults
Command Modes
Command History
Usage Guidelines
This command is used to troubleshoot inconsistencies that occur in the Cisco Express Forwarding event log between the routes in the Routing Information Base (RIB), Route Processor (RP) Cisco Express Forwarding tables, and line card Cisco Express Forwarding tables.
The Cisco Express Forwarding event log collects Cisco Express Forwarding events as they occur without debugging enabled. This process allows the tracing of an event immediately after it occurs. Cisco technical personnel may ask for information from this event log to aid in resolving problems with the Cisco Express Forwarding feature.
When the Cisco Express Forwarding table event log has reached its capacity, the oldest event is written over by the newest event until the event log size is reset using this command or cleared using the clear ip cef event-log command.
Examples
The following example shows how to set the Cisco Express Forwarding table event log size to 5000 entries:
Related Commands
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Enables Cisco Express Forwarding table consistency checker types and parameters. |
ip cef table resolution-timer
Note The ip cef table resolution-timer command is not available in Cisco IOS Releases 12.2(25)S, 12.2(28)SB, 12.2(33)SRA, 12.2(33)SXH, 12.4(20)T and later releases.
To change the Cisco Express Forwarding background resolution timer, use the ip cef table resolution-timer command in global configuration mode.
ip cef table resolution-timer seconds
no ip cef table resolution-timer seconds
Syntax Description
Timer value in seconds. Range is from 0 to 30 seconds; 0 is for the automatic exponential backoff scheme. |
Defaults
The default configuration value is 0 seconds for automatic exponential backoff.
Command Modes
Command History
Usage Guidelines
The Cisco Express Forwarding background resolution timer can use either a fixed time interval or an exponential backoff timer that reacts to the amount of resolution work required. The exponential backoff timer starts at 1 second, increasing to 16 seconds when a network flap is in progress. When the network recovers, the timer returns to 1 second.
The default is used for the exponential backoff timer. During normal operation, the default configuration value set to 0 results in re-resolution occurring much sooner than when the timer is set at a higher fixed interval.
Examples
The following example show how to set the Cisco Express Forwarding background resolution timer to 3 seconds:
ip cef traffic-statistics
To change the time interval that controls when Next Hop Resolution Protocol (NHRP) sets up or tears down a switched virtual circuit (SVC), use the ip cef traffic-statistics command in global configuration mode. To restore the default values, use the no form of this command.
ip cef traffic-statistics [ load-interval seconds ] [ update-rate seconds ]
Syntax Description
Defaults
Command Modes
Command History
Usage Guidelines
The ip nhrp trigger-svc command sets the threshold by which NHRP sets up and tears down a connection. The threshold is the Cisco Express Forwarding traffic load statistics. The thresholds in the ip nhrp trigger-svc command are measured during a sampling interval of 30 seconds, by default. To change that interval over which that threshold is determined, use the load-interval seconds option of the ip cef traffic-statistics command.
When NHRP is configured on a Cisco Express Forwarding switching node with a Versatile Interface Processor (VIP2) adapter, you must make sure the update-rate keyword is set to 5 seconds.
Other Cisco IOS features could also use the ip cef traffic-statistics command; this NHRP feature relies on it.
Examples
In the following example, the triggering and teardown thresholds are calculated based on an average over 120 seconds:
Related Commands
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Configures when NHRP will set up and tear down an SVC based on aggregate traffic rates. |
ip load-sharing
To enable load balancing for Cisco Express Forwarding on an interface, use the ip load-sharing command in interface configuration mode. To disable load balancing for Cisco Express Forwarding on the interface, use the no form of this command.
ip load-sharing { per-packet | per-destination }
Syntax Description
Command Default
Per-destination load balancing is enabled by default when you enable Cisco Express Forwarding.
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
Per-packet load balancing allows the router to send data packets over successive equal-cost paths without regard to individual destination hosts or user sessions. Path utilization is good, but packets destined for a given destination host might take different paths and might arrive out of order.
Note Per-packet load balancing via Cisco Express Forwarding is not supported on Engine 2 Cisco 12000 series Internet router line cards (LCs).
Per-destination load balancing allows the router to use multiple, equal-cost paths to achieve load sharing. Packets for a given source-destination host pair are guaranteed to take the same path, even if multiple, equal-cost paths are available. Traffic for different source-destination host pairs tends to take different paths.
Note If you want to enable per-packet load sharing to a particular destination, then all interfaces that can forward traffic to the destination must be enabled for per-packet load sharing.
Note Per-packet load balancing can result in out-of-sequence (OOS) packet delivery errors on some routers, which can cause applications such as VoIP to malfunction. Therefore, per-packet load balancing is not recommended. For more information, see the release notes and caveats for your platform and software release.
Cisco ASR 1000 Series Aggregation Services Routers
The ip load-sharing command is not supported on the Cisco ASR 1000 Series Aggregation Services Router. Per-packet load balancing is not supported. On the Cisco ASR 1000 Series Aggregation Services Router, per-destination load balancing is enabled by default and cannot be disabled.
Examples
The following example shows how to enable per-packet load balancing:
The following example shows how to enable per-destination load balancing:
Related Commands
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ip route-cache
To control the use of switching methods for forwarding IP packets, use the ip route-cache command in interface configuration mode. To disable any of these switching methods, use the no form of this command.
ip route-cache [ c ef | distributed | flow | policy | same-interface ]
no ip route-cache [ c ef | distributed | flow | policy | same-interface ]
Syntax Description
Command Default
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
Note The Cisco 10000 series routers do not support the ip route-cache command.
Using the route cache is often called fast switching. The route cache allows outgoing packets to be load-balanced on a per-destination basis rather than on a per-packet basis. The ip route-cache command with no additional keywords enables fast switching.
Entering the ip route-cache command has no effect on a subinterface. Subinterfaces accept the no form of the command; however, this disables Cisco Express Forwarding or distributed Cisco Express Forwarding on the physical interface and all subinterfaces associated with the physical interface
The default behavior for Fast Switching varies by interface and media.
Note IPv4 fast switching is removed with the implementation of the Cisco Express Forwarding infrastructure enhancements for Cisco IOS 12.2(25)S-based releases and Cisco IOS Release 12.4(20)T. For these and later Cisco IOS releases, switching path are Cisco Express Forwarding switched or process switched.
You can enable IP fast switching when the input and output interfaces are the same interface, using the ip route-cache same-interface command. This configuration normally is not recommended, although it is useful when you have partially meshed media, such as Frame Relay or you are running Web Cache Communication Protocol (WCCP) redirection. You could use this feature on other interfaces, although it is not recommended because it would interfere with redirection of packets to the optimal path.
The flow caching option can be used in conjunction with Cisco Express Forwarding switching to enable NetFlow, which allows statistics to be gathered with a finer granularity. The statistics include IP subprotocols, well-known ports, total flows, average number of packets per flow, and average flow lifetime.
Note The ip route-cache flow command has the same functionality as the ip flow ingress command, which is the preferred command for enabling NetFlow. If either the ip route-cache flow command or the
ip flow ingress command is configured, both commands will appear in the output of the
show running-config command.
The distributed option is supported on Cisco routers with line cards and Versatile Interface Processors (VIPs) that support Cisco Express Forwarding switching.
On Cisco routers with Route/Switch Processor (RSP) and VIP controllers, the VIP hardware can be configured to switch packets received by the VIP with no per-packet intervention on the part of the RSP. When VIP distributed switching is enabled, the input VIP interface tries to switch IP packets instead of forwarding them to the RSP for switching. Distributed switching helps decrease the demand on the RSP.
If the ip route-cache distributed, ip cef distributed, and ip route-cache flow commands are configured, the VIP performs distributed Cisco Express Forwarding switching and collects a finer granularity of flow statistics.
IP Route-Cache Cisco Express Forwarding
In some instances, you might want to disable Cisco Express Forwarding or distributed Cisco Express Forwarding on a particular interface because that interface is configured with a feature that
Cisco Express Forwarding or distributed Cisco Express Forwarding does not support. Because all interfaces that support Cisco Express Forwarding or distributed Cisco Express Forwarding are enabled by default when you enable Cisco Express Forwarding or distributed Cisco Express Forwarding operation globally, you must use the no form of the ip route-cache distributed command in the interface configuration mode to turn Cisco Express Forwarding or distributed Cisco Express Forwarding operation off a particular interface.
Disabling Cisco Express Forwarding or distributed Cisco Express Forwarding on an interface disables Cisco Express Forwarding or distributed Cisco Express Forwarding switching for packets forwarded to the interface, but does not affect packets forwarded out of the interface.
Additionally, when you disable distributed Cisco Express Forwarding on the RSP, Cisco IOS software switches packets using the next-fastest switch path (Cisco Express Forwarding).
Enabling Cisco Express Forwarding globally disables distributed Cisco Express Forwarding on all interfaces. Disabling Cisco Express Forwarding or distributed Cisco Express Forwarding globally enables process switching on all interfaces.
Note On the Cisco 12000 series Internet router, you must not disable distributed Cisco Express Forwarding on an interface.
If Cisco Express Forwarding is already enabled, the ip route-cache route command is not required because PBR packets are Cisco Express Forwarding-switched by default.
Before you can enable fast-switched PBR, you must first configure PBR.
FSPBR supports all of PBR’s match commands and most of PBR’s set commands, with the following restrictions:
- The set ip default next-hop and set default interface commands are not supported.
- The set interface command is supported only over point-to-point links, unless a route cache entry exists using the same interface specified in the set interface command in the route map.
Also, at the process level, the routing table is consulted to determine if the interface is on a reasonable path to the destination. During fast switching, the software does not make this check. Instead, if the packet matches, the software blindly forwards the packet to the specified interface.
Note Not all switching methods are available on all platforms. Refer to the Cisco Product Catalog for information about features available on the platform you are using.
Examples
Configuring Fast Switching and Disabling Cisco Express Forwarding Switching
The following example shows how to enable fast switching and disable Cisco Express Forwarding switching:
The following example shows that fast switching is enabled:
The following example shows that Cisco Express Forwarding switching is disabled:
The following example shows the configuration information for FastEthernet interface 0/0/0:
The following example shows how to enable Cisco Express Forwarding (and to disable distributed
Cisco Express Forwarding if it is enabled):
The following example shows how to enable VIP distributed Cisco Express Forwarding and per-flow accounting on an interface (regardless of the previous switching type enabled on the interface):
The following example shows how to enable Cisco Express Forwarding on the router globally (which also disables distributed Cisco Express Forwarding on any interfaces that are running distributed
Cisco Express Forwarding), and disable Cisco Express Forwarding (which enables process switching) on Ethernet interface 0:
The following example shows how to enable distributed Cisco Express Forwarding operation on the router (globally), and disable Cisco Express Forwarding operation on Ethernet interface 0:
The following example shows how to reenable distributed Cisco Express Forwarding operation on Ethernet interface 0:
Configuring Fast Switching for Traffic That Is Received and Transmitted over the Same Interface
The following example shows how to enable fast switching and disable Cisco Express Forwarding switching:
The following example shows that fast switching on the same interface is enabled for interface fastethernet 0/0/0:
The following example shows the configuration information for FastEthernet interface 0/0/0:
The following example shows how to enable NetFlow switching:
The following example shows that NetFlow accounting is enabled for FastEthernet interface 0/0/0:
Configuring Distributed Switching
The following example shows how to enable distributed switching:
The following example shows that distributed Cisco Express Forwarding switching is for FastEthernet interface 0/0/0:
Configuring Fast Switching for PBR
The following example shows how to configure a simple policy-based routing scheme and to enable FSPBR:
The following example shows that FSPBR is enabled for FastEthernet interface 0/0/0:
Related Commands
ip route-cache policy
The policy keyword for the ip route-cache command is no longer documented as a separate command.
The information for using the policy keyword for the ip route-cache command has been incorporated into the ip route-cache command documentation. See the ip route-cache command documentation for more information.
ip verify unicast notification threshold
To configure the threshold value used to determine whether to send a Unicast Reverse Path Forwarding (RPF) drop rate notification, use the ip verify unicast notification threshold command in interface configuration mode. To set the notification threshold back to the default value, use the no form of this command.
ip verify unicast notification threshold packets-per-second
no ip verify unicast notification threshold
Syntax Description
Threshold value, in packets per second, used to determine whether to send a Unicast RPF drop rate notification. The range is from 0 to 4294967295. The default is 1000. |
Command Default
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
This command configures the threshold Unicast RPF drop rate which, when exceeded, triggers a notification. Configuring a value of 0 means that any Unicast RPF packet drop triggers a notification.
Examples
The following example shows how to configure a notification threshold value of 900 on Ethernet interface 3/0:
Router(config# interface ethernet 3/0
Related Commands
ip verify unicast reverse-path
Note This command was replaced by the ip verify unicast source reachable-via command effective with Cisco IOS Release 12.0(15)S. The ip verify unicast source reachable-via command allows for more flexibility and functionality, such as supporting asymmetric routing, and should be used for any Reverse Path Forward implementation. The ip verify unicast reverse-path command is still supported.
To enable Unicast Reverse Path Forwarding (Unicast RPF), use the ip verify unicast reverse-path command in interface configuration mode. To disable Unicast RPF, use the no form of this command.
ip verify unicast reverse-path [ list ]
no ip verify unicast reverse-path [ list ]
Syntax Description
(Optional) Specifies a numbered access control list (ACL) in the following ranges: |
Command Default
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
Use the ip verify unicast reverse-path interface command to mitigate problems caused by malformed or forged (spoofed) IP source addresses that are received by a router. Malformed or forged source addresses can indicate denial of service (DoS) attacks on the basis of source IP address spoofing.
When Unicast RPF is enabled on an interface, the router examines all packets that are received on that interface. The router checks to ensure that the source address appears in the Forwarding Information Base (FIB) and that it matches the interface on which the packet was received. This “look backwards” ability is available only when Cisco Express Forwarding is enabled on the router because the lookup relies on the presence of the FIB. Cisco Express Forwarding generates the FIB as part of its operation.
To use Unicast RPF, enable Cisco Express Forwarding switching or distributed Cisco Express Forwarding switching in the router. There is no need to configure the input interface for Cisco Express Forwarding switching. As long as Cisco Express Forwarding is running on the router, individual interfaces can be configured with other switching modes.
Note It is very important for Cisco Express Forwarding to be configured globally in the router. Unicast RPF will not work without Cisco Express Forwarding.
Note Unicast RPF is an input function and is applied on the interface of a router only in the ingress direction.
The Unicast Reverse Path Forwarding feature checks to determine whether any packet that is received at a router interface arrives on one of the best return paths to the source of the packet. The feature does this by doing a reverse lookup in the Cisco Express Forwarding table. If Unicast RPF does not find a reverse path for the packet, Unicast RPF can drop or forward the packet, depending on whether an ACL is specified in the Unicast Reverse Path Forwarding command. If an ACL is specified in the command, then when (and only when) a packet fails the Unicast RPF check, the ACL is checked to determine whether the packet should be dropped (using a deny statement in the ACL) or forwarded (using a permit statement in the ACL). Whether a packet is dropped or forwarded, the packet is counted in the global IP traffic statistics for Unicast RPF drops and in the interface statistics for Unicast RPF.
If no ACL is specified in the Unicast Reverse Path Forwarding command, the router drops the forged or malformed packet immediately and no ACL logging occurs. The router and interface Unicast RPF counters are updated.
Unicast RPF events can be logged by specifying the logging option for the ACL entries used by the Unicast Reverse Path Forwarding command. Log information can be used to gather information about the attack, such as source address, time, and so on.
Where to Use RPF in Your Network
Unicast RPF may be used on interfaces in which only one path allows packets from valid source networks (networks contained in the FIB). Unicast RPF may also be used in cases for which a router has multiple paths to a given network, as long as the valid networks are switched via the incoming interfaces. Packets for invalid networks will be dropped. For example, routers at the edge of the network of an Internet service provider (ISP) are likely to have symmetrical reverse paths. Unicast RPF may still be applicable in certain multi-homed situations, provided that optional Border Gateway Protocol (BGP) attributes such as weight and local preference are used to achieve symmetric routing.
With Unicast RPF, all equal-cost “best” return paths are considered valid. This means that Unicast RPF works in cases where multiple return paths exist, provided that each path is equal to the others in terms of the routing cost (number of hops, weights, and so on) and as long as the route is in the FIB. Unicast RPF also functions where Enhanced Internet Gateway Routing Protocol (EIGRP) variants are being used and unequal candidate paths back to the source IP address exist.
For example, routers at the edge of the network of an ISP are more likely to have symmetrical reverse paths than routers that are in the core of the ISP network. Routers that are in the core of the ISP network have no guarantee that the best forwarding path out of the router will be the path selected for packets returning to the router. In this scenario, you should use the new form of the command, ip verify unicast source reachable-via, if there is a chance of asymmetrical routing.
Examples
The following example shows that the Unicast Reverse Path Forwarding feature has been enabled on a serial interface:
The following example uses a very simple single-homed ISP to demonstrate the concepts of ingress and egress filters used in conjunction with Unicast RPF. The example illustrates an ISP-allocated classless interdomain routing (CIDR) block 192.168.202.128/28 that has both inbound and outbound filters on the upstream interface. Be aware that ISPs are usually not single-homed. Hence, provisions for asymmetrical flows (when outbound traffic goes out one link and returns via a different link) need to be designed into the filters on the border routers of the ISP.
The following example demonstrates the use of ACLs and logging with Unicast RPF. In this example, extended ACL 197 provides entries that deny or permit network traffic for specific address ranges. Unicast RPF is configured on Ethernet interface 0 to check packets arriving at that interface.
For example, packets with a source address of 192.168.201.10 arriving at Ethernet interface 0 are dropped because of the deny statement in ACL 197. In this case, the ACL information is logged (the logging option is turned on for the ACL entry) and dropped packets are counted per-interface and globally. Packets with a source address of 192.168.201.100 arriving at Ethernet interface 0 are forwarded because of the permit statement in ACL 197. ACL information about dropped or suppressed packets is logged (the logging option is turned on for the ACL entry) to the log server.
Related Commands
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Enables Cisco Express Forwarding on the route processor card. |
ip verify unicast source reachable-via
To enable Unicast Reverse Path Forwarding (Unicast RPF), use the ip verify unicast source reachable-via command in interface configuration mode. To disable Unicast RPF, use the no form of this command.
ip verify unicast source reachable-via { any | rx [ l2-src ]} [ allow-default ] [ allow-self-ping ] [ access - list ]
no ip verify unicast source reachable-via
Syntax Description
Command Default
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
Use the ip verify unicast source reachable-via interface command to mitigate problems caused by malformed or forged (spoofed) IP source addresses that pass through a router. Malformed or forged source addresses can indicate DoS attacks based on source IP address spoofing.
To use Unicast RPF, enable Cisco Express Forwarding or distributed Cisco Express Forwarding in the router. There is no need to configure the input interface for Cisco Express Forwarding. As long as Cisco Express Forwarding is running on the router, individual interfaces can be configured with other switching modes.
Note It is important for Cisco Express Forwarding to be configured globally on the router. Unicast RPF does not work without Cisco Express Forwarding.
Note Unicast RPF is an input function and is applied on the interface of a router only in the ingress direction.
When Unicast RPF is enabled on an interface, the router examines all packets that are received on that interface. The router checks to make sure that the source address appears in the FIB. If the rx keyword is selected, the source address must match the interface on which the packet was received. If the any keyword is selected, the source address must be present only in the FIB. This ability to “look backwards” is available only when Cisco Express Forwarding is enabled on the router because the lookup relies on the presence of the FIB. Cisco Express Forwarding generates the FIB as part of its operation.
Note If the source address of an incoming packet is resolved to a null adjacency, the packet will be dropped. The null interface is treated as an invalid interface by the new form of the Unicast RPF command. The older form of the command syntax did not exhibit this behavior.
Unicast RPF checks to determine whether any packet that is received at a router interface arrives on one of the best return paths to the source of the packet. If a reverse path for the packet is not found, Unicast RPF can drop or forward the packet, depending on whether an ACL is specified in the Unicast RPF command. If an ACL is specified in the command, when (and only when) a packet fails the Unicast RPF check, the ACL is checked to determine whether the packet should be dropped (using a deny statement in the ACL) or forwarded (using a permit statement in the ACL). Whether a packet is dropped or forwarded, the packet is counted in the global IP traffic statistics for Unicast RPF drops and in the interface statistics for Unicast RPF.
If no ACL is specified in the ip verify unicast source reachable-via command, the router drops the forged or malformed packet immediately, and no ACL logging occurs. The router and interface Unicast RPF counters are updated.
Unicast RPF events can be logged by specifying the logging option for the ACL entries that are used by the ip verify unicast source reachable-via command. Log information can be used to gather information about the attack, such as source address, time, and so on.
If the source address is in the FIB and reachable only through the interface on which the packet was received, the packet is passed. The syntax for this method is ip verify unicast source reachable-via rx.
Exists-Only (or Loose Mode) RPF
If the source address is in the FIB and reachable through any interface on the router, the packet is passed. The syntax for this method is ip verify unicast source reachable-via any.
Because this Unicast RPF option passes packets regardless of which interface the packet enters, it is often used on Internet service provider (ISP) routers that are “peered” with other ISP routers (where asymmetrical routing typically occurs). Packets using source addresses that have not been allocated on the Internet, which are often used for spoofed source addresses, are dropped by this Unicast RPF option. All other packets that have an entry in the FIB are passed.
Normally, sources found in the FIB but only by way of the default route will be dropped. Specifying the allow-default keyword option will override this behavior. You must specify the allow-default keyword in the command to permit Unicast RPF to successfully match on prefixes that are known through the default route to pass these packets.
This keyword allows the router to ping its own interface or interfaces. By default, when Unicast RPF is enabled, packets that are generated by the router and destined to the router are dropped, thereby, making certain troubleshooting and management tasks difficult to accomplish. Issue the allow-self-ping keyword to enable self-pinging.
Use Unicast RPF strict mode on interfaces where only one path allows packets from valid source networks (networks contained in the FIB). Also, use Unicast RPF strict mode when a router has multiple paths to a given network, as long as the valid networks are switched through the incoming interfaces. Packets for invalid networks will be dropped. For example, routers at the edge of the network of an ISP are likely to have symmetrical reverse paths. Unicast RPF strict mode is applicable in certain multihomed situations, provided that optional Border Gateway Protocol (BGP) attributes, such as weight and local preference, are used to achieve symmetric routing.
Note With Unicast RPF, all equal-cost “best” return paths are considered valid. This means that Unicast RPF works in cases where multiple return paths exist, provided that each path is equal to the others in terms of the routing cost (number of hops, weights, and so on) and as long as the route is in the FIB. Unicast RPF also functions where Enhanced Internet Gateway Routing Protocol (EIGRP) variants are being used and unequal candidate paths back to the source IP address exist.
Use Unicast RPF loose mode on interfaces where asymmetric paths allow packets from valid source networks (networks contained in the FIB). Routers that are in the core of the ISP network have no guarantee that the best forwarding path out of the router will be the path selected for packets returning to the router.
IP and MAC Address Spoof Prevention
In Release 15.0(1)M and later, you can use the l2-src keyword to enable source IPv4 and source MAC address binding. To disable source IPv4 and source MAC address binding, use the no form of the ip verify unicast source reachable-via command.
If an inbound packet fails this security check, it will be dropped and the Unicast RPF dropped-packet counter will be incremented. The only exception occurs if a numbered access control list has been specified as part of the Unicast RPF command in strict mode, and the ACL permits the packet. In this case the packet will be forwarded and the Unicast RPF suppressed-drops counter will be incremented.
Note The l2-src keyword cannot be used with the loose uRPF command, ip verify unicast source reachable-via any command.
Not all platforms support the l2-src keyword. Therefore, not all the possible keyword combinations for strict Unicast RPF in the following list will apply to your platform:
Possible keyword combinations for strict Unicast RPF include the following:
Examples
Single-Homed ISP Connection with Unicast RPF
The following example uses a very simple single-homed ISP connection to demonstrate the concept of Unicast RPF. In this example, an ISP peering router is connected through a single serial interface to one upstream ISP. Hence, traffic flows into and out of the ISP will be symmetric. Because traffic flows will be symmetric, a Unicast RPF strict-mode deployment can be configured.
ACLs and Logging with Unicast RPF
The following example demonstrates the use of ACLs and logging with Unicast RPF. In this example, extended ACL 197 provides entries that deny or permit network traffic for specific address ranges. Unicast RPF is configured on interface Ethernet 0/1/1 to check packets arriving at that interface.
For example, packets with a source address of 192.168.201.10 arriving at interface Ethernet 0/1/1 are dropped because of the deny statement in ACL 197. In this case, the ACL information is logged (the logging option is turned on for the ACL entry) and dropped packets are counted per-interface and globally. Packets with a source address of 192.168.201.100 arriving at interface Ethernet 0/1/2 are forwarded because of the permit statement in ACL 197. ACL information about dropped or suppressed packets is logged (the logging option is turned on for the ACL entry) to the log server.
MAC Address Binding on Software Switching Platforms Like the Cisco 7200 Series Routers
The following example shows how to enable source IPv4 and source MAC address binding on Ethernet 0/0:
Related Commands
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Enables Cisco Express Forwarding on the route processor card. |
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ip verify unicast vrf
To enable Unicast Reverse Path Forwarding (Unicast RPF) verification for a specified VRF, use the ip verify unicast vrf command in interface configuration mode. To disable the Unicast RPF check for a VRF, use the no form of this command.
ip verify unicast vrf vrf-name { deny | permit }
no ip verify unicast vrf vrf-name { deny | permit }
Syntax Description
Command Default
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
Unicast RPF is configured to verify that the source address is in the Forwarding Information Base (FIB). The ip verify unicast vrf command is configured in interface configuration mode and is enabled for each VRF. This command has permit and deny keywords that are used to determine if traffic is forwarded or dropped after Unicast RPF verification.
Examples
The following example configures Unicast RPF verification for VRF1 and VRF2. VRF1 traffic is forwarded. VRF2 traffic is dropped.
Related Commands
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Configures an import map to import IPv4 prefixes from the global routing table to a VRF table. |
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ipv6 cef
To enable Cisco Express Forwarding for IPv6, use the ipv6 cef command in global configuration mode. To disable Cisco Express Forwarding for IPv6, use the no form of this command.
Syntax Description
Command Default
Command Modes
Command History
Usage Guidelines
The ipv6 cef command is similar to the ip cef command, except that it is IPv6-specific.
The ipv6 cef command is not available on the Cisco 12000 series Internet routers because this distributed platform operates only in distributed Cisco Express Forwarding for IPv6 mode.
Note The ipv6 cef command is not supported in interface configuration mode.
Note Some distributed architecture platforms, such as the Cisco 7500 series routers, support both Cisco Express Forwarding for IPv6 and distributed Cisco Express Forwarding for IPv6. When Cisco Express Forwarding for IPv6 is configured on distributed platforms, Cisco Express Forwarding switching is performed by the Route Processor (RP).
Note You must enable Cisco Express Forwarding for IPv4 by using the ip cef global configuration command before enabling Cisco Express Forwarding for IPv6 by using the ipv6 cef global configuration command.
Cisco Express Forwarding for IPv6 is advanced Layer 3 IP switching technology that functions the same and offer the same benefits as Cisco Express Forwarding for IPv4. Cisco Express Forwarding for IPv6 optimizes network performance and scalability for networks with dynamic, topologically dispersed traffic patterns, such as those associated with web-based applications and interactive sessions.
Examples
The following example enables standard Cisco Express Forwarding for IPv4 operation and then standard Cisco Express Forwarding for IPv6 operation globally on the router.
Related Commands
ipv6 cef accounting
To enable Cisco Express Forwarding for IPv6 and distributed Cisco Express Forwarding for IPv6 network accounting, use the ipv6 cef accounting command in global configuration mode or interface configuration mode. To disable Cisco Express Forwarding for IPv6 network accounting, use the no form of this command.
ipv6 cef accounting accounting-types
no ipv6 cef accountin g accounting-types
Specific Cisco Express Forwarding Accounting Information Through Interface Configuration Mode
ipv6 cef accounting non-recursive { external | internal }
no ipv6 cef accounting non-recursive { external | internal }
Syntax Description
Command Default
Cisco Express Forwarding for IPv6 network accounting is disabled by default.
Command Modes
Global configuration (config)
Interface configuration (config-if)
Command History
Usage Guidelines
The ipv6 cef accounting command is similar to the ip cef accounting command, except that it is IPv6-specific.
Configuring Cisco Express Forwarding for IPv6 network accounting enables you to collect statistics on Cisco Express Forwarding for IPv6 traffic patterns in your network.
When you enable network accounting for Cisco Express Forwarding for IPv6 by using the ipv6 cef accounting command in global configuration mode, accounting information is collected at the Route Processor (RP) when Cisco Express Forwarding for IPv6 mode is enabled and at the line cards when distributed Cisco Express Forwarding for IPv6 mode is enabled. You can then display the collected accounting information using the show ipv6 cef EXEC command.
For prefixes with directly connected next hops, the non-recursive keyword enables express forwarding of the collection of packets and bytes through a prefix. This keyword is optional when this command is used in global configuration mode after you enter another keyword on the ipv6 cef accounting command.
This command in interface configuration mode must be used in conjunction with the global configuration command. The interface configuration command allows a user to specify two different bins (internal or external) for the accumulation of statistics. The internal bin is used by default. The statistics are displayed through the show ipv6 cef detail command.
Per-destination load balancing uses a series of 16 hash buckets into which the set of available paths are distributed. A hash function operating on certain properties of the packet is applied to select a bucket that contains a path to use. The source and destination IP addresses are the properties used to select the bucket for per-destination load balancing. Use the load-balance-hash keyword with the ipv6 cef accounting command to enable per-hash-bucket counters. Enter the show ipv6 cef prefix internal command to display the per-hash-bucket counters.
Examples
The following example enables the collection of Cisco Express Forwarding for IPv6 accounting information for prefixes with directly connected next hops:
Related Commands
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Enable Cisco Express Forwarding network accounting (for IPv4). |
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Displays information about packets forwarded by Cisco Express Forwarding. |
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ipv6 cef distributed
To enable distributed Cisco Express Forwarding for IPv6, use the ipv6 cef distributed command in global configuration mode. To disable Cisco Express Forwarding for IPv6, use the no form of this command.
Syntax Description
Command Default
Distributed Cisco Express Forwarding for IPv6 is disabled on the Cisco 7500 series routers and enabled on the Cisco 12000 series Internet routers.
Command Modes
Command History
Usage Guidelines
The ipv6 cef distributed command is similar to the ip cef distributed command, except that it is IPv6-specific.
Enabling distributed Cisco Express Forwarding for IPv6 globally on the router by using the ipv6 cef distributed in global configuration mode distributes the Cisco Express Forwarding processing of IPv6 packets from the Route Processor (RP) to the line cards of distributed architecture platforms.
Note The ipv6 cef distributed command is not supported on the Cisco 12000 series Internet routers because distributed Cisco Express Forwarding for IPv6 is enabled by default on this platform.
Note To forward distributed Cisco Express Forwarding for IPv6 traffic on the router, configure the forwarding of IPv6 unicast datagrams globally on your router by using the ipv6 unicast-routing global configuration command, and configure an IPv6 address and IPv6 processing on an interface by using the ipv6 address interface configuration command.
Note You must enable distributed Cisco Express Forwarding for IPv4 by using the ip cef distributed global configuration command before enabling distributed Cisco Express Forwarding for IPv6 by using the ipv6 cef distributed global configuration command.
Cisco Express Forwarding is advanced Layer 3 IP switching technology. Cisco Express Forwarding optimizes network performance and scalability for networks with dynamic, topologically dispersed traffic patterns, such as those associated with web-based applications and interactive sessions.
Examples
The following example enables distributed Cisco Express Forwarding for IPv6 operation:
Related Commands
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Controls the use of high-speed switching caches for IP routing. |
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ipv6 cef load-sharing algorithm
To select a Cisco Express Forwarding load-balancing algorithm for IPv6, use the ipv6 cef load-sharing algorithm command in global configuration mode. To return to the default universal load-balancing algorithm, use the no form of this command.
ipv6 cef load-sharing algorithm { original | universal [ id ] | include-ports { source [ id ] | [ destination ] [ id ] | source [ id ] destination [ id ]}}
no ipv6 cef load-sharing algorithm
Syntax Description
Command Default
The universal load-balancing algorithm is selected. If you do not configure the fixed identifier for a load-balancing algorithm, the router automatically generates a unique ID.
Command Modes
Command History
Usage Guidelines
The ipv6 cef load-sharing algorithm command is similar to the ip cef load-sharing algorithm command, except that it is IPv6-specific.
When the Cisco Express Forwarding for IPv6 load-balancing algorithm is set to universal mode, each router on the network can make a different load-sharing decision for each source-destination address pair.
The include-ports algorithm allows you to use the Layer 4 source and destination ports as part of the load-balancing decision. This method benefits traffic streams running over equal-cost paths that are not load-shared because the majority of the traffic is between peer addresses that use different port numbers, such as Real-Time Protocol (RTP) streams.
Examples
The following example shows how to enable the Cisco Express Forwarding load-balancing algorithm for IPv6 for Layer-4 source and destination ports:
The router automatically generates fixed IDs for the algorithm.
Related Commands
ipv6 cef optimize neighbor resolution
To configure address resolution optimization from Cisco Express Forwarding for IPv6 for directly connected neighbors, use the ipv6 cef optimize neighbor resolution command in global configuration mode. To disable address resolution optimization from Cisco Express Forwarding for IPv6 for directly connected neighbors, use the no form of this command.
ipv6 cef optimize neighbor resolution
no ipv6 cef optimize neighbor resolution
Syntax Description
Command Default
If this command is not configured, Cisco Express Forwarding for IPv6 does not optimize the address resolution of directly connected neighbors.
Command Modes
Command History
Usage Guidelines
The ipv6 cef optimize neighbor resolution command is very similar to the ip cef optimize neighbor resolution command, except that it is IPv6-specific.
Use this command to trigger Layer 2 address resolution of neighbors directly from Cisco Express Forwarding for IPv6.
Examples
The following example shows how to optimize address resolution from Cisco Express Forwarding for IPv6 for directly connected neighbors:
Related Commands
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Configures address resolution optimization from Cisco Express Forwarding for IPv4 for directly connected neighbors. |
ipv6 verify unicast reverse-path
To enable Unicast Reverse Path Forwarding (Unicast RPF) for IPv6, use the ipv6 verify unicast reverse-path command in interface configuration mode. To disable Unicast RPF, use the no form of this command.
ipv6 verify unicast reverse-path [ access-list name ]
no ipv6 verify unicast reverse-path [ access-list name ]
Syntax Description
(Optional) Specifies the name of the access list. Note This keyword and argument are not supported on the Cisco 12000 series Internet router. |
Command Default
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
The ipv6 verify unicast reverse-path command is used to enable Unicast RPF for IPv6 in strict checking mode. The Unicast RPF for IPv6 feature requires that Cisco Express Forwarding for IPv6 is enabled on the router.
Note Beginning in Cisco IOS Release 12.0(31)S, the Cisco 12000 series Internet router supports both the ipv6 verify unicast reverse-path and ipv6 verify unicast source reachable-via rx commands to enable Unicast RPF to be compatible with the Cisco IOS Release 12.3T and 12.2S software trains.
Use the ipv6 verify unicast reverse-path command to mitigate problems caused by malformed or forged (spoofed) IP source addresses that pass through a router. Malformed or forged source addresses can indicate denial-of-service (DoS) attacks based on source IP address spoofing.
When Unicast RPF is enabled on an interface, the router examines all packets received on that interface. The router checks to make sure that the source IPv6 address appears in the routing table and that it is reachable by a path through the interface on which the packet was received. Unicast RPF is an input feature and is applied only on the input interface of a router at the upstream end of a connection.
The Unicast RPF feature performs a reverse lookup in the CEF table to check if any packet received at a router interface has arrived on a path identified as a best return path to the source of the packet. If a reverse path for the packet is not found, Unicast RPF can drop or forward the packet, depending on whether an ACL is specified in the Unicast RPF command. If an ACL is specified in the command, then when (and only when) a packet fails the Unicast RPF check, the ACL is checked to determine whether the packet should be dropped (using a deny statement in the ACL) or forwarded (using a permit statement in the ACL). Whether a packet is dropped or forwarded, the packet is counted in the global IP traffic statistics for Unicast RPF drops and in the interface statistics for Unicast RPF.
If no ACL is specified in the Unicast RPF command, the router drops the forged or malformed packet immediately and no ACL logging occurs. The router and interface Unicast RPF counters are updated.
Unicast RPF events can be logged by specifying the logging option for the ACL entries used by the Unicast RPF command. Log information can be used to gather information about the attack, such as source address, time, and so on.
Note When you configure Unicast RPF for IPv6 on the Cisco 12000 series Internet router, the most recently configured checking mode is not automatically applied to all interfaces as on other platforms. You must enable Unicast RPF for IPv6 separately on each interface.
When you configure a SPA on the Cisco 12000 series Internet router, the interface address is in the format slot/subslot/port.
The optional access-list keyword for the ipv6 verify unicast reverse-path command is not supported on the Cisco 12000 series Internet router. For information about how Unicast RPF can be used with ACLs on other platforms to mitigate the transmission of invalid IPv4 addresses (perform egress filtering) and to prevent (deny) the reception of invalid IPv4 addresses (perform ingress filtering), refer to the “Configuring Unicast Reverse Path Forwarding” chapter in the “Other Security Features” section of the Cisco IOS Security Configuration Guide.
Note When using Unicast RPF, all equal-cost “best” return paths are considered valid. This means that Unicast RPF works in cases where multiple return paths exist, provided that each path is equal to the others in terms of the routing cost (number of hops, weights, and so on).
Do not use Unicast RPF on core-facing interfaces that are internal to the network. Internal interfaces are likely to have routing asymmetry, meaning that there are multiple routes to the source of a packet. Apply Unicast RPF only where there is natural or configured symmetry.
For example, routers at the edge of the network of an Internet service provider (ISP) are more likely to have symmetrical reverse paths than routers that are in the core of the ISP network. Routers that are in the core of the ISP network have no guarantee that the best forwarding path out of the router will be the path selected for packets returning to the router. Hence, it is not recommended that you apply Unicast RPF where there is a chance of asymmetric routing. It is simplest to place Unicast RPF only at the edge of a network or, for an ISP, at the customer edge of the network.
Examples
Unicast Reverse Path Forwarding on a Serial Interface
The following example shows how to enable the Unicast RPF feature on a serial interface:
Unicast Reverse Path Forwarding on a Cisco 12000 Series Internet Router
The following example shows how to enable Unicast RPF for IPv6 with strict checking on a 10G SIP Gigabit Ethernet interface 2/1/2:
Unicast Reverse Path Forwarding on a Single-Homed ISP
The following example uses a very simple single-homed ISP to demonstrate the concepts of ingress and egress filters used in conjunction with Unicast RPF. The example illustrates an ISP-allocated classless interdomain routing (CIDR) block 209.165.202.128/28 that has both inbound and outbound filters on the upstream interface. Be aware that ISPs are usually not single-homed. Hence, provisions for asymmetrical flows (when outbound traffic goes out one link and returns via a different link) need to be designed into the filters on the border routers of the ISP.
The following example demonstrates the use of ACLs and logging with Unicast RPF. In this example, extended ACL abc provides entries that deny or permit network traffic for specific address ranges. Unicast RPF is configured on interface Ethernet 0/0 to check packets arriving at that interface.
For example, packets with a source address of 8765:4321::1 arriving at Ethernet interface 0 are dropped because of the deny statement in ACL “abc.” In this case, the ACL information is logged (the logging option is turned on for the ACL entry) and dropped packets are counted per-interface and globally. Packets with a source address of 1234:5678::1 arriving at Ethernet interface 0/0 are forwarded because of the permit statement in ACL abc. ACL information about dropped or suppressed packets is logged (the logging option is turned on for the ACL entry) to the log server.
Related Commands
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Enables Cisco Express Forwarding on the route processor card. |
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ipv6 verify unicast source reachable-via
To verify that a source address exists in the FIB table and enable Unicast Reverse Path Forwarding (Unicast RPF), use the ipv6 verify unicast source reachable-via command in interface configuration mode. To disable URPF, use the no form of this command.
ipv6 verify unicast source reachable-via { rx | any } [ allow-default ] [ allow-self-ping ] [ access-list-name ]
Syntax Description
Command Default
Command Modes
Interface configuration (config-if)
Command History
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This command was integrated into Cisco IOS Release 12.2(28)SB. |
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This command was introduced on Cisco ASR 1000 Series Aggregation Services Routers. |
Usage Guidelines
The ipv6 verify unicast reverse-path command is used to enable Unicast RPF for IPv6 in loose checking mode.
Use the ipv6 verify unicast source reachable-via command to mitigate problems caused by malformed or forged (spoofed) IP source addresses that pass through an IPv6 router. Malformed or forged source addresses can indicate denial-of-service (DoS) attacks based on source IPv6 address spoofing.
The URPF feature checks to see if any packet received at a router interface arrives on one of the best return paths to the source of the packet. The feature does this by doing a reverse lookup in the CEF table. If URPF does not find a reverse path for the packet, U RPF can drop or forward the packet, depending on whether an access control list (ACL) is specified in the ipv6 verify unicast source reachable-via command. If an ACL is specified in the command, then when (and only when) a packet fails the URPF check, the ACL is checked to see if the packet should be dropped (using a deny statement in the ACL) or forwarded (using a permit statement in the ACL). Whether a packet is dropped or forwarded, the packet is counted in the global IP traffic statistics for U RPF drops and in the interface statistics for Unicast RPF.
If no ACL is specified in the ipv6 verify unicast source reachable-via command, the router drops the forged or malformed packet immediately and no ACL logging occurs. The router and interface Unicast RPF counters are updated.
U RPF events can be logged by specifying the logging option for the ACL entries used by the ipv6 verify unicast source reachable-via command. Log information can be used to gather information about the attack, such as source address, time, and so on.
Examples
The following example enables Unicast RPF on any interface:
Related Commands
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Defines an IPv6 access list and places the router in IPv6 access list configuration mode. |
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Displays the usability status of interfaces configured for IPv6. |
mls cef maximum-routes
To limit the maximum number of the routes that can be programmed in the hardware allowed per protocol, use the mls cef maximum-routes command in global configuration mode. To return to the default settings, use the no form of this command.
mls cef maximum-routes { ip | ip-multicast | ipv6 | mpls } maximum-routes
no mls cef maximum-routes { ip | ip-multicast | ipv6 | mpls }
Syntax Description
Maximum number of the routes that can be programmed in the hardware allowed per protocol. |
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Specifies the maximum number of Multiprotocol Label Switching (MPLS) labels. |
Command Default
– IPv4 unicast and MPLS—512,000 routes
– IPv6 unicast and IPv4 multicast—256,000 routes
– IPv4 unicast and MPLS—192,000 routes
– IPv6 unicast and IPv4 multicast—32,000 routes
Note See the “Usage Guidelines” section for information on XL and non-XL mode systems.
Command Modes
Command History
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This command was integrated into Cisco IOS Release 12.2(33)SRA. |
|
This command was integrated into Cisco IOS Release 12.2(33)SXH. |
Usage Guidelines
Note If you copy a configuration file that contains the multilayer switching (MLS) Cisco Express Forwarding maximum routes into the startup-config file and reload the Cisco 7600 series router, the Cisco 7600 series router reloads after it reboots.
This command is not supported on Cisco 7600 series routers that are configured with a Supervisor Engine 2.
The mls cef maximum-routes command limits the maximum number of the routes that can be programmed in the hardware. If routes are detected that exceed the limit for that protocol, an exception condition is generated.
The determination of XL and non-XL mode is based on the type of Policy Feature Card (PFC) or Distributed Forwarding Card (DFC) modules that are installed in your system. For additional information on systems running Cisco IOS software release 12.2SXF and earlier releases see:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/release/notes/OL_4164.html#Policy_Feature_Card_Guidelines_and_Restrictions
For additional information on systems running Cisco IOS software release 12.2SXH and later releases see:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/release/notes/ol_14271.html#Policy_Feature_Card_Guidelines_and_Restrictions
The valid values for the maximum-routes argument depend on the system mode—XL mode or non-XL mode. The valid values are as follows:
– IP and MPLS—Up to 1,007,000 routes
– IP multicast and IPv6—Up to 503,000 routes
– IP and MPLS—Up to 239,000 routes
– IP multicast and IPv6—Up to 119,000 routes
Note The maximum values that you are permitted to configure is not fixed but varies depending on the values that are allocated for other protocols.
An example of how to enter the maximum routes argument is as follows:
where 4 is 4096 IP routes (1024 x4 = 4096).
The new configurations are applied after a system reload only and do not take effect if a switchover occurs.
Note A switchover might lead to a crash when you have a VSS in a dual supervisor setup due to a lack of synchronization between the TCAM.
In RPR mode, if you change and save the maximum-routes configuration, the redundant supervisor engine reloads when it becomes active from either a switchover or a system reload. The reload occurs 5 minutes after the supervisor engine becomes active.
Use the show mls cef maximum-routes command to display the current maximum routes system configuration.
Examples
This example shows how to set the maximum number of routes that are allowed per protocol:
Router(config)#
mls cef maximum-routes ip 100
This example shows how to return to the default setting for a specific protocol:
Router(config)#
no mls cef maximum-routes ip
Related Commands
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mls cef tunnel fragment
To allow tunnel fragmentation, use the mls cef tunnel fragment command. To return to the default settings, use the no form of this command.
Syntax Description
Command Default
Command Modes
Command History
Usage Guidelines
When you enable tunnel fragmentation, if the size of the packets that are going into a tunnel interface exceed the MTU, the packet is fragmented. The packets that are fragmented are reassembled at the destination point.
Examples
This example shows how to allow tunnel fragmentation:
Router(config)#
mls cef tunnel fragment
This example shows how to return to the default setting:
Router(config)#
no mls cef tunnel fragment
Related Commands
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mls erm priority
To assign the priorities to define an order in which protocols attempt to recover from the exception status, use the mls erm priority command in global configuration mode. To return to the default settings, use the no form of this command.
Note The mls erm priority command is not available in Cisco IOS Release 12.2(33)SXJ and later Cisco IOS 12.2SX releases.
mls erm priority ipv4 value ipv6 value mpls value
no mls erm priority ipv4 value ipv6 value mpls value
Syntax Description
Prioritizes the Multiprotocol Label Switching (MPLS) protocol. The default priority is 3. |
Command Default
Command Modes
Command History
Usage Guidelines
This command is not supported on Cisco 7600 series routers that are configured with a Supervisor Engine 2.
A lower value indicates a higher priority.
When a protocol sees a Forwarding Information Base (FIB) table exception, the protocol notifies the FIB Embedded Resource Manager (ERM). The FIB ERM periodically polls the FIB table exception status and decides which protocol gets priority over another protocol when multiple protocols are running under the exception. Only one protocol can attempt to recover from an exception at any time.
If there is sufficient FIB space, the protocol with the highest priority tries to recover first. Other protocols under the exception do not start to recover until the previous protocol completes the recovery process by reloading the appropriate FIB table.
Examples
This example shows how to set the ERM exception-recovery priority:
Router(config)#
mls erm priority ipv4 2 ipv6 1 mpls 3
This example shows how to return to the default setting:
Router(config)#
no mls erm priority ipv4 2 ipv6 1 mpls 3
Related Commands
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Displays information about the Cisco Express Forwarding exception. |
mls ip
To enable multilayer switching (MLS) IP for the internal router on the interface, use the mls ip command in interface configuration mode. To disable MLS IP on the interface use the no form of this command.
Syntax Description
Defaults
Command Modes
Interface configuration (config-if)
Command History
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Support for this command on the Supervisor Engine 2 was extended to Release 12.2(17d)SXB. |
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This command was integrated into Cisco IOS Release 12.2(33)SRA. |
Usage Guidelines
This command is not supported on Cisco 7600 series routers that are configured with a Supervisor Engine 720.
Examples
This example shows how to enable MLS IP:
Router(config-if)#
mls ip
Related Commands
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Allows the external systems to enable MLS IP on a specified interface. |
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mls ip cef accounting per-prefix
To enable Multilayer Switching (MLS) per-prefix accounting, use the mls ip cef accounting per-prefix command in global configuration mode. To disable MLS per-prefix accounting, use the no form of this command
mls ip cef accounting per-prefix prefix-entry prefix-entry-mask [ instance-name ]
no mls ip cef accounting per-prefix
Syntax Description
(Optional) Virtual Private Network (VPN) routing and forwarding instance name. |
Command Default
Command Modes
Command History
Usage Guidelines
Per-prefix accounting collects the adjacency counters used by the prefix. When the prefix is used for accounting, the adjacency cannot be shared with other prefixes. You can use per-prefix accounting to account for the packets sent to a specific destination.
Examples
This example shows how to enable MLS per-prefix accounting:
Router(config)#
mls ip cef accounting per-prefix 172.20.52.18 255.255.255.255
This example shows how to disable MLS per-prefix accounting:
Router(config)#
no mls ip cef accounting per-prefix
Related Commands
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Displays all the prefixes that are configured for the statistic collection. |
mls ip cef load-sharing
To configure the Cisco Express Forwarding load balancing, use the mls ip cef load-sharing command in global configuration mode. To return to the default settings, use the no form of this command.
mls ip cef load-sharing [ full ] [ exclude-port { destination | source }] [ simple ]
Syntax Description
Defaults
Source and destination IP address and universal identification
Command Modes
Command History
Usage Guidelines
The mls ip cef load-sharing command affects the IPv4, the IPv6, and the Multiprotocol Label Switching (MPLS) forwardings.
The mls ip cef load-sharing command is structured as follows:
- mls ip cef load-sharing full —Uses Layer 3 and Layer 4 information with multiple adjacencies.
- mls ip cef load-sharing full simple —Uses Layer 3 and Layer 4 information without multiple adjacencies.
- mls ip cef load-sharing simple —Uses Layer 3 information without multiple adjacencies.
For additional guidelines, refer to the Cisco 7600 Series Router Cisco IOS Software Configuration Guide .
Examples
This example shows how to set load balancing to include Layer 3 and Layer 4 ports with multiple adjacencies:
This example shows how to set load balancing to exclude the destination Layer 4 ports and source and destination IP addresses (Layer 3) from the load-balancing algorithm:
This example shows how to set load balancing to exclude the source Layer 4 ports and source and destination IP addresses (Layer 3) from the load-balancing algorithm:
This example shows how to return to the default setting:
Related Commands
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Displays the IP entries in the MLS-hardware Layer 3-switching table. |
mls ip cef rate-limit
To rate-limit Cisco Express Forwarding-punted data packets, use the mls ip cef rate-limit command in global configuration mode. To disable the rate-limited Cisco Express Forwarding-punted data packets, use the no form of this command.
mls ip cef rate-limit packets-per-second
Syntax Description
Number of data packets per second; see the “Usage Guidelines” section for the valid values. |
Defaults
Command Modes
Command History
Usage Guidelines
The valid values for the number of data packets per second are as follows:
- For Cisco 7600 series routers that are configured with a Supervisor Engine 2, the valid values are from 1 to 1000000.
- For Cisco 7600 series routers that are configured with a Supervisor Engine 720, the valid values are from 0 to 1000000.
Certain denial-of-service attacks target the route processing engines of routers. Certain packets that cannot be forwarded by the Policy Feature Card (PFC) are directed to the Multilayer Switch Feature Card (MSFC) for processing. Denial-of-service attacks can overload the route processing engine and cause routing instability when running dynamic routing protocols. You can use the mls ip cef rate-limit command to limit the amount of traffic that is sent to the MSFC to prevent denial-of-service attacks against the route processing engine.
This command rate limits all Cisco Express Forwarding-punted data packets including the following:
- Data packets going to the local interface IP address
- Data packets requiring Address Resolution Protocol (ARP)
Setting the rate to a low value could impact the packets that are destined to the IP addresses of the local interfaces and the packets that require ARP.
You should use this command to limit these packets to a normal rate and to avoid abnormal incoming rates.
For additional guidelines, see the Cisco 7600 Series Router Cisco IOS Software Configuration Guide .
Examples
This example shows how to enable and set rate limiting:
Router(config)#
mls ip cef rate-limit 50000
Related Commands
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Displays the IP entries in the MLS-hardware Layer 3-switching table. |
mls ip cef rpf hw-enable-rpf-acl
To enable hardware unicast Reverse Path Forwarding (uRPF) for packets matching the deny Access Control List (ACL) when uRPF with ACL is enabled, use the mls ip cef rpf hw-enable-rpf-acl command in global configuration mode. To disable hardware uRPF when RPF and ACL are enabled, use the no form of this command.
mls ip cef rpf hw-enable-rpf-acl
no mls ip cef rpf hw-enable-rpf-acl
Syntax Description
Command Default
Command Modes
Command History
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Usage Guidelines
This command is supported on systems configured with a PFC3 (Supervisor Engine 720 and Supervisor Engine 32) only.
If you do not enter the mls ip cef rpf hw-enable-rpf-acl command, when the uRPF with ACL is specified, packets that are permitted by the uRPF ACL are forwarded in hardware and the denied packets are sent to the Multilayer Switching Feature Card (MSFC) for the uRPF check. This command enables hardware forwarding with the uRPF check for the packets that are denied by the uRPF ACL. However, in this case packets permitted by the uRPF ACL are sent to the MSFC for forwarding.
Examples
This example shows how to enable hardware uRPF when RPF and ACL are enabled:
This example shows how to disable hardware uRPF when RPF and ACL are enabled:
Related Commands
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mls ip cef rpf interface-group
To define an interface group in the Reverse Path Forwarding (RPF)-VLAN table, use the mls ip cef rpf interface-group command in global configuration mode. To delete the interface group, use the no form of this command.
mls ip cef rpf interface-group group-number interface1 interface2 interface3 [ ... ]
no mls ip cef rpf interface-group group-number interface1 interface2 interface3 [ ... ]
Syntax Description
Interface number; see the “Usage Guidelines” section for formatting guidelines. |
|
(Optional) Additional interface numbers; see the “Usage Guidelines” section for additional information. |
Defaults
Command Modes
Command History
|
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Support for this command was introduced on the Supervisor Engine 720. |
|
This command was integrated into Cisco IOS Release 12.2(33)SRA. |
Usage Guidelines
This command is not supported on Cisco 7600 series routers that are configured with a Supervisor Engine 2.
A single interface group contains three to six interfaces. You can configure up to four interface groups. For each interface group, the first four entries are installed in the hardware RPF-VLAN table.
Enter the interface as interface-typemod/port .
Separate each interface entry with a space. You do not have to include a space between the interface-type and the mod/port arguments. See the “Examples” section for a sample entry.
Examples
This example shows how to define an interface group:
Router(config)#
mls ip cef rpf interface-group 0 F2/1 F2/2 F2/3 F2/4 F2/5 F2/6
mls ip cef rpf multipath
To configure the Reverse Path Forwarding (RPF) modes, use the mls ip cef rpf multipath command in global configuration mode. To return to the default settings, use the no form of this command.
mls ip cef rpf multipath { interface-group | punt | pass }
no mls ip cef rpf multipath { interface-group | punt | pass }
Syntax Description
Defaults
Command Modes
Command History
|
|
---|---|
Support for this command was introduced on the Supervisor Engine 720. |
|
This command was integrated into Cisco IOS Release 12.2(33)SRA. |
Usage Guidelines
This command is not supported on Cisco 7600 series routers that are configured with a Supervisor Engine 2.
The interface-group mode is similar to the pass mode but utilizes the RPF_VLAN global table for the RPF check. Packets from other multiple path prefixes always pass the RPF check.
You enter the mls ip cef rpf multipath interface-group command to define an RPF_VLAN table interface group. One interface group contains from three to six interfaces, and you can configure up to four interface groups. For each interface group, the first four entries are installed in the hardware RPF_VLAN table. For the prefix that has more than three multiple paths, and all paths except two are part of that interface group, the FIB entry of that prefix uses this RPF_VLAN entry.
Examples
This example shows how to redirect the RPF-failed packets to the route processor for multiple path prefix support:
Router(config)#
mls ip cef rpf multipath interface-group
Related Commands
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Displays the IP entries in the MLS-hardware Layer 3-switching table. |
monitor elog trigger position
To monitor system events using event-logging control and trigger control parameters, use the monitor elog trigger position command in privileged EXEC configuration mode.
monitor elog trigger position position-percentage
Syntax Description
The position of the trigger in the buffer expressed in percentage. |
Command Default
Command Modes
Command History
|
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This command was introduced in a release earlier than Cisco IOS Release 15.0(1)M. |
Examples
The following example shows how to monitor 50 percent of the system events using event-logging control and trigger control parameters:
Related Commands
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monitor event-trace (EXEC)
To monitor and control the event trace function for a specified Cisco IOS software subsystem component, use the monitor event-trace command in privileged EXEC mode.
monitor event-trace component { clear | continuous | disable | dump [ pretty ] | enable | one-shot }
monitor event-trace component { disable | dump | enable | size | stacktrace }
Catalyst 6500 Series Switches and Cisco 7600 Series Routers
monitor event-trace all-traces { continuous [ cancel ] | dump [ merged ] [ pretty ]}
monitor event-trace l3 { clear | continuous [ cancel ] | disable | dump [ pretty ] | enable | interface type mod / port | one-shot }
monitor event-trace spa { clear | continuous [ cancel ] | disable | dump [ pretty ] | enable | one-shot }
monitor event-trace subsys { clear | continuous [ cancel ] | disable | dump [ pretty ] | enable | one-shot }
Syntax Description
Command Default
Command Modes
Command History
Usage Guidelines
Use the monitor event-trace command to control what, when, and how event trace data is collected. Use this command after you have configured the event trace functionality on the networking device using the monitor event-trace command in global configuration mode.
Note The amount of data collected from the trace depends on the trace message size configured using the monitor event-trace command in global configuration mode for each instance of a trace.
The Cisco IOS software allows for the subsystem components to define whether support for event tracing is enabled or disabled at boot time. You can enable or disable event tracing in two ways: using the monitor event-trace command in privileged EXEC mode or using the monitor event-trace command in global configuration mode. To disable event tracing, you would enter either of these commands with the disable keyword. To enable event tracing again, you would enter either of these commands with the enable keyword.
To determine whether you can enable event tracing on a subsystem, use the monitor event-trace ? command to get a list of software components that support event tracing. To determine whether event tracing is enabled by default for the subsystem, use the show monitor event-trace command to display trace messages.
Use the show monitor event-trace command to display trace messages. Use the monitor event-trace component dump command to save trace message information for a single event. By default, trace information is saved in binary format. If you want to save trace messages in ASCII format, possibly for additional application processing, use the monitor event-trace component dump pretty command.
To write the trace messages for all events currently enabled on a networking device to a file, enter the monitor event-trace dump command.
To configure the file where you want to save trace information, use the monitor event-trace command in global configuration mode. The trace messages are saved in a binary format.
Examples
The following example shows the privileged EXEC commands to stop event tracing, clear the current contents of memory, and reenable the trace function for the interprocess communication (IPC) component. This example assumes that the tracing function is configured and enabled on the networking device.
The following example shows how the monitor event-trace one-shot command accomplishes the same function as the previous example except in one command. In this example, once the size of the trace message file has been exceeded, the trace is terminated.
The following example shows the command for writing trace messages for an event in binary format. In this example, the trace messages for the IPC component are written to a file.
The following example shows the command for writing trace messages for an event in ASCII format. In this example, the trace messages for the MBUS component are written to a file.
Catalyst 6500 Series Switches and Cisco 7600 Series Routers Examples Only
This example shows how to stop event tracing, clear the current contents of memory, and reenable the trace function for the SPA component. This example assumes that the tracing function is configured and enabled on the networking device.
Related Commands
monitor event-trace (global)
To configure event tracing for a specified Cisco IOS software subsystem component, use the monitor event-trace command in global configuration mode.
monitor event-trace component { disable | dump-file filename | enable | size number | stacktrace number } timestamps [ datetime [ localtime ] [ msec ] [ show-timezone ] | uptime ]
monitor event-trace component { disable | dump-file filename | enable | clear | continuous | one-shot }
Syntax Description
Command Default
Event tracing is enabled or disabled depending on the software component.
Command Modes
Command History
Usage Guidelines
Use the monitor event-trace command to enable or disable event tracing and to configure event trace parameters for Cisco IOS software subsystem components.
Note Event tracing is intended for use as a software diagnostic tool and should be configured only under the direction of a Technical Assistance Center (TAC) representative. In Cisco IOS software images that do not provide subsystem support for the event trace function, the monitor event-trace command is not available.
The Cisco IOS software allows the subsystem components to define whether support for event tracing is enabled or disabled by default. The command interface for event tracing allows you to change the default two ways: using the monitor event-trace command in privileged EXEC mode or using the monitor event-trace command in global configuration mode.
Additionally, default settings do not show up in the configuration file. If the subsystem software enables event tracing by default, the monitor event-trace component enable command will not show up in the configuration file of the networking device; however, disabling event tracing that has been enabled by default by the subsystem will create a command entry in the configuration file.
Note The amount of data collected from the trace depends on the trace message size configured using the monitor event-trace command for each instance of a trace.
To determine whether you can enable event tracing on a subsystem, use the monitor event-trace ? command to get a list of software components that support event tracing.
To determine whether event tracing is enabled by default for the subsystem, use the show monitor event-trace command to display trace messages.
To specify the trace call stack at tracepoints, you must first clear the trace buffer.
Examples
The following example shows how to enable event tracing for the interprocess communication (IPC) subsystem component in Cisco IOS software and configure the size to 4096 messages. The trace messages file is set to ipc-dump in slot0 (flash memory).
When you select Cisco Express Forwarding as the component for which to enable event tracing, you can use the following additional arguments and keywords: monitor event-trace cef [ events | interface | ipv6 | ipv4 ][ all ]. The following example shows how to enable event tracing for IPv4 or IPv6 events of the Cisco Express Forwarding component in Cisco IOS software:
Related Commands
monitor event-trace cef (EXEC)
To monitor and control the event trace function for Cisco Express Forwarding, use the monitor event-trace cef command in privileged EXEC mode.
monitor event-trace cef { dump [ merged pretty | pretty ] | { events | interface | ipv4 | ipv6 } { clear | continuous [ cancel ] | disable | dump [ pretty ] | enable | one-shot }}
Syntax Description
Command Default
Event tracing for Cisco Express Forwarding is enabled by default.
Command Modes
Command History
Usage Guidelines
Use the monitor event-trace cef command to control what, when, and how Cisco Express Forwarding event trace data is collected. Use this command after you have configured the event trace functionality on the networking device using the monitor event-trace cef command in global configuration mode.
Note The amount of data collected from the trace depends on the trace message size configured using the monitor event-trace cef command in global configuration mode for each instance of a trace.
You can enable or disable Cisco Express Forwarding event tracing in one of two ways: using the monitor event-trace cef command in privileged EXEC mode or using the monitor event-trace cef command in global configuration mode. To disable event tracing, you would enter either of these commands with the disable keyword. To enable event tracing again, you would enter either of these commands with the enable keyword.
Use the show monitor event-trace cef command to display trace messages. Use the monitor event-trace cef dump command to save trace message information for a single event. By default, trace information is saved in binary format. If you want to save trace messages in ASCII format, possibly for additional application processing, use the monitor event-trace cef dump pretty command.
To configure the file in which you want to save trace information, use the monitor event-trace cef command in global configuration mode. The trace messages are saved in a binary format.
Examples
The following example shows the privileged EXEC commands that stop event tracing, clear the current contents of memory, and reenable the trace function for Cisco Express Forwarding events. This example assumes that the tracing function is configured and enabled on the networking device.
The following example shows how to configure the continuous display of the latest Cisco Express Forwarding event trace entries for IPv4 events:
The following example shows how to stop the continuous display of the latest trace entries:
Related Commands
monitor event-trace cef (global)
To configure event tracing for Cisco Express Forwarding, use the monitor event-trace cef command in global configuration mode. To disable event tracing for Cisco Express Forwarding, use the no form of this command.
monitor event-trace cef { dump-file dump-file-name | { events | interface } { disable | dump-file dump-file-name | enable | size number | stacktrace [ depth ]}}
no monitor event-trace cef { dump-file dump-file-name | { events | interface } { disable | dump-file dump-file-name | enable | size | stacktrace [ depth ]}}
Syntax Description
Command Default
Event tracing for Cisco Express Forwarding is enabled by default.
Command Modes
Command History
Usage Guidelines
Use the monitor event-trace cef command to enable or disable event tracing and to configure event trace parameters for Cisco Express Forwarding.
The Cisco IOS software allows Cisco Express Forwarding to define whether support for event tracing is enabled or disabled by default. The command interface for event tracing allows you to change the default value in one of two ways: using the monitor event-trace cef command in privileged EXEC mode or using the monitor event-trace cef command in global configuration mode.
Additionally, default settings do not appear in the configuration file. If Cisco Express Forwarding enables event tracing by default, the monitor event-trace cef enable command does not appear in the configuration file of the networking device; however, disabling event tracing that has been enabled by default by the subsystem creates a command entry in the configuration file.
Note The amount of data collected from the trace depends on the trace message size configured using the monitor event-trace cef command for each instance of a trace.
To determine whether event tracing is enabled by default for Cisco Express Forwarding, use the show monitor event-trace cef command to display trace messages.
To specify the trace call stack at tracepoints, you must first clear the trace buffer.
Examples
The following example shows how to enable event tracing for Cisco Express Forwarding and configure the buffer size to 5000 messages. The trace messages file is set to cef-dump in slot0 (flash memory).
Related Commands
monitor event-trace cef ipv4 (global)
To configure event tracing for Cisco Express Forwarding IPv4 events, use the monitor event-trace cef ipv4 command in global configuration mode. To disable event tracing for Cisco Express Forwarding IPv4 events, use the no form of this command.
monitor event-trace cef ipv4 { disable | distribution | dump-file dump-file-name | enable | match { global | ip-address mask } | size number | stacktrace [ depth ] | vrf vrf-name [ distribution | match { global | ip-address mask }]}
no monitor event-trace cef { ipv4 { disable | distribution | dump-file dump-file-name | enable | match | size | stacktrace [ depth ]} | vrf }
Syntax Description
Command Default
Event tracing for Cisco Express Forwarding IPv4 events is enabled by default.
Command Modes
Command History
Usage Guidelines
Use the monitor event-trace cef ipv4 command to enable or disable event tracing for Cisco Express Forwarding IPv4 events.
The Cisco IOS software allows Cisco Express Forwarding to define whether support for event tracing is enabled or disabled by default. The command interface for event tracing allows you to change the default value in one of two ways: using the monitor event-trace cef ipv4 command in privileged EXEC mode or using the monitor event-trace cef ipv4 command in global configuration mode.
Note The amount of data collected from the trace depends on the trace message size configured using the monitor event-trace cef ipv4 command for each instance of a trace.
To determine whether event tracing is enabled by default for Cisco Express Forwarding, use the show monitor event-trace cef ipv4 command to display trace messages.
To specify the trace call stack at tracepoints, you must first clear the trace buffer.
Examples
The following example shows how to enable event tracing for Cisco Express Forwarding IPv4 events and configure the buffer size to 5000 messages:
Related Commands
monitor event-trace cef ipv6 (global)
To configure event tracing for Cisco Express Forwarding IPv6 events, use the monitor event-trace cef ipv6 command in global configuration mode. To disable event tracing for Cisco Express Forwarding, use the no form of this command.
monitor event-trace cef ipv6 { disable | distribution | dump-file dump-file-name | enable | match { global | ipv6-address / n } | size number | stacktrace [ depth ] | vrf vrf-name [ distribution | match { global | ipv6-address / n }]}
no monitor event-trace cef ipv6 { disable | distribution | dump-file dump-file-name | enable | match | size | stacktrace [ depth ] | vrf }
Syntax Description
Command Default
Event tracing for Cisco Express Forwarding IPv6 events is enabled by default.
Command Modes
Command History
Usage Guidelines
Use the monitor event-trace cef ipv6 command to enable or disable event tracing for Cisco Express Forwarding IPv6 events.
The Cisco IOS software allows Cisco Express Forwarding to define whether support for event tracing is enabled or disabled by default. The command interface for event tracing allows you to change the default value in one of two ways: using the monitor event-trace cef ipv6 command in privileged EXEC mode or using the monitor event-trace cef ipv6 command in global configuration mode.
Note The amount of data collected from the trace depends on the trace message size configured using the monitor event-trace cef ipv6 command for each instance of a trace.
To determine whether event tracing is enabled by default for Cisco Express Forwarding IPv6 events, use the show monitor event-trace cef ipv6 command to display trace messages.
To specify the trace call stack at tracepoints, you must first clear the trace buffer.
Examples
The following example shows how to enable event tracing for Cisco Express Forwarding IPv6 events and configure the buffer size to 10000 messages.