- Preface
- Product Overview
- Command-Line Interfaces
- Configuring the Switch for the First Time
- Administering the Switch
- Configuring Virtual Switching Systems
- Configuring the Cisco IOS In-Service Software Upgrade Process
- Configuring the Cisco IOS XE In Service Software Upgrade Process
- Configuring Interfaces
- Checking Port Status and Connectivity
- Configuring Trustsec
- RPR
- Configuring Supervisor Engine Redundancy Using RPR and SSO on Supervisor Engine 7-E and Supervisor Engine 7L-E
- Configuring Cisco NSF with SSO Supervisor Engine Redundancy
- Environmental Monitoring and Power Management
- Configuring Power over Ethernet
- Configuring the Catalyst 4500 Series Switch with Cisco Network Assistant
- Configuring VLANs, VTP, and VMPS
- Configuring IP Unnumbered Interface
- Configuring Layer 2 Ethernet Interfaces
- Configuring SmartPort Macros
- Configuring Cisco IOS Auto Smartport Macros
- Configuring STP and MST
- Configuring Flex Links and MAC Address-Table Move Update
- Configuring Resilient Ethernet Protocol
- Configuring Optional STP Features
- Configuring EtherChannel and Link State Tracking
- Configuring IGMP Snooping and Filtering, and MVR
- Configuring IPv6 MLD Snooping
- Configuring 802.1Q Tunneling, VLAN Mapping, and Layer 2 Protocol Tunneling
- Configuring CDP
- Configuring LLDP, LLDP-MED, and Location Service
- Configuring UDLD
- Configuring Unidirectional Ethernet
- Configuring Layer 3 Interfaces
- Configuring Cisco Express Forwarding
- Configuring Unicast Reverse Path Forwarding
- Configuring IP Multicast
- Configuring ANCP Client
- Configuring Bidirectional Forwarding Detection
- Configuring Policy-Based Routing
- Configuring VRF-lite
- Configuring Quality of Service
- Configuring Voice Interfaces
- Configuring Private VLANs
- Configuring MACsec Encryption
- Configuring 802.1X Port-Based Authentication
- Configuring the PPPoE Intermediate Agent
- Configuring Web-Based Authentication
- Configuring Port Security
- Configuring Control Plane Policing and Layer 2 Control Packet QoS
- Configuring Dynamic ARP Inspection
- Configuring DHCP Snooping, IP Source Guard, and IPSG for Static Hosts
- Configuring Network Security with ACLs
- Support for IPv6
- Port Unicast and Multicast Flood Blocking
- Configuring Storm Control
- Configuring SPAN and RSPAN
- Configuring Wireshark
- Configuring Enhanced Object Tracking
- Configuring System Message Logging
- Onboard Failure Logging (OBFL)
- Configuring SNMP
- Configuring NetFlow-lite
- Configuring Flexible NetFlow
- Configuring Ethernet OAM and CFM
- Configuring Y.1731 (AIS and RDI)
- Configuring Call Home
- Configuring Cisco IOS IP SLA Operations
- Configuring RMON
- Performing Diagnostics
- Configuring WCCP Version 2 Services
- Configuring MIB Support
- ROM Monitor
- Acronyms and Abbreviations
- configIX
Configuring Policy-Based Routing
This chapter describes the tasks for configuring policy-based routing (PBR) on a Catalyst 4500 series switch and includes these major sections:
- About Policy-Based Routing
- Policy-Based Routing Configuration Tasks
- Policy-Based Routing Configuration Examples
Note
For complete syntax and usage information for the switch commands used in this chapter, see the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:
http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html
If a command is not in the Catalyst 4500 Series Switch Command Reference, you can locate it in the Cisco IOS library. See the Cisco IOS Command Reference and related publications at this location:
http://www.cisco.com/en/US/products/ps6350/index.html
Note To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release.
About Policy-Based Routing
This section contains the following subsections:
PBR gives you a flexible method of routing packets by allowing you to define policies for traffic flows, lessening reliance on routes derived from routing protocols. PBR gives you more control over routing by extending and complementing the existing mechanisms provided by routing protocols. PBR allows you to specify paths for certain traffic, such as priority traffic over a high-cost link.
You can set up PBR as a way to route packets based on configured policies. For example, you can implement routing policies to allow or deny paths based on the identity of a particular end system, or an application protocol.
PBR allows you to perform the following tasks:
- Classify traffic based on extended access list criteria. Access lists, and then establish the match criteria.
- Route packets to specific traffic-engineered paths.
Policies can be based on IP address, port numbers, or protocols. For a simple policy, use any one of these descriptors; for a complicated policy, all of them.
About PBR
All packets received on an interface with PBR enabled (except those sent directly to the switch IP) are handled by enhanced packet filters known as route maps. The route maps used by PBR dictate the policy, determining to where the packets are forwarded.
Route maps are composed of statements, which can be marked as permit or deny. They are interpreted in the following ways:
- If a statement is marked as deny, the packets meeting the match criteria are sent back using the normal forwarding channels and destination-based routing is performed.
- If the statement is marked as permit and a packet matches the access-lists, then the first valid set clause is applied to that packet.
This is explained in more detail in the section Understanding Route-Maps.
You specify PBR on the incoming interface (the interface on which packets are received), not outgoing interface.
Understanding Route-Maps
PBR is implemented by applying a route-map on an incoming interface. A given interface can have only one route-map configured.
A route-map is configured at the global configuration parser mode. You can then apply this route-map on one or more interfaces (in the interface configuration parser sub-mode).
A route-map is comprised of one or more route-map statements. Each statement has a sequence number, as well as a permit or deny clause.
Each route-map statement contains match and set commands. The match command denotes the match criteria to be applied on the packet data. The set command denote the PBR action to be taken on the packet.
The following example shows a single route-map called rm-test and six route-map statements:
The numbers 21, 22,... 26 are the sequence numbers of the route-map statements.
PBR Route-Map Processing Logic
When a packet is received on an interface configured with a route-map, the forwarding logic processes each route-map statement according to the sequence number.
If the route-map statement encountered is a route-map... permit statement:
- The packet is matched against the criteria in the match command. This command may refer to an ACL that may itself have one or more permit and/or deny expressions. The packet is matched against the expressions in the ACL, and a permit/deny decision is reached.
- If the decision reached is permit, then the PBR logic executes the action specified by the set command on the packet.
- If the decision reached is deny, then the PBR action (specified in the set command) is not applied. Instead the processing logic moves forward to look at the next route-map statement in the sequence (the statement with the next higher sequence number). If no next statement exists, PBR processing terminates, and the packet is routed using the default IP routing table.
If the route-map statement encountered is a route-map... deny statement:
- The packet is matched against the criteria given in the match command. This command may refer to an ACL that may itself have one or more permit and/or deny expressions. The packet is matched against the expressions in the ACL, and a permit/deny decision is reached.
- If the criteria decision is permit, then the PBR processing terminates, and the packet is routed using the default IP routing table.
- If the criteria decision is deny, then the PBR processing logic moves forward to look at the next route-map statement in the sequence (the statement with the next higher sequence number). If no next statement exists, PBR processing terminates, and the packet is routed using the default IP routing table.
Note The set command has no effect inside a route-map... deny statement.
A route-map statement can have multiple set commands, which are applied in the following priority:
If both the set ip next-hop and set ip next-hop recursive commands are present in the same route-map statement, the next-hop set command is applied.
If the set ip next-hop command is not available then the set ip next-hop recursive command is applied.
If the set ip recursive-next-hop and the set interface command are not present, then the packet is routed using the default routing table; it is not dropped. If the packet is required to be dropped, use the set next-hop recursive command followed by a set interface null0 configuration command.
Load balancing with recursive next-hop
If multiple equal-cost routes to the subnet have been configured by the set ip next-hop recursive command, load balancing will occur only if all the adjacencies to the routes are resolved. If any of the adjacencies have not been resolved, then load balancing will not happen and only one of the routes whose adjacency is resolved will be used. If none of the adjacencies are resolved, then packets will be processed in software, resulting in at least one of the adjacencies to be resolved and programmed in hardware. PBR relies on routing protocols or other means to resolve all adjacencies and make load balancing happen.
PBR Route-Map Processing Logic Example
Consider a route-map called rm-test defined as follows:
– Matches ACL 101 in sequence #21.
– PBR is switched through next-hop 21.1.1.1.
Note ACL 101 is also matched in sequence #23, but the processing doesn't reach that point
– In sequence #21, the ACL 101 action denies this packet (because all ACLs have an implicit deny). Processing advances to sequence #22.
– In sequence #22, ACL 102 matches TCP port 102, but the ACL action is deny. Processing advances to sequence #23.
– In sequence #23, ACL 2102 matches TCP port 102, and the ACL action is permit.
– Packet is switched to output interface VLAN 23.
– Processing moves from sequence #21 to #24, because all ACLs in these sequence numbers have a deny action for port 105.
– In sequence #25, ACL 105 has a permit action for TCP port 105.
– The route-map deny takes effect, and the packet is routed using the default IP routing table.
The Catalyst 4500 series switch supports matching route-map actions with a packet by installing entries in the TCAM that match the set of packets described by the ACLs in the match criteria of the route map. These TCAM entries point at adjacencies that either perform the necessary output actions or forward the packet to software if either hardware does not support the action or its resources are exhausted.
If the route-map specifies a set interface … action, packets that match the match statement are routed in software. Similarly, if the route-map specifies a set default interface… action and there is no matching IP route for the packet, the packet is routed in software.
Note The scale of hardware-based PBR is determined by TCAM size and the time required for the CPU to flatten the ACL before programming into hardware. The latter will noticeably increase if a PBR policy requires a considerable number of class-maps. For example, a PBR policy of 1,200 class-maps may require 60-90 minutes of "flatten" time before programming into hardware. This process may repeat if an adjacency change requires PBR reprogramming.
Using Policy-Based Routing
You can enable PBR to change the routing path of certain packets from the default path that would be chosen by IP routing. For example, you can use PBR to provide the following functionality:
- Equal access
- Protocol-sensitive routing
- Source-sensitive routing
- Routing based on interactive versus batch traffic
- Routing based on dedicated links
Some applications or traffic can benefit from source-specific routing; for example, you can transfer stock records to a corporate office on a higher-bandwidth, higher-cost link for a short time while sending routine application data, such as e-mail, over a lower-bandwidth, lower-cost link.
Note PBR configuration is only allowed on interfaces belonging to the global routing table. PBR is not supported on interfaces that belong to VRFs.
Policy-Based Routing Configuration Tasks
To configure PBR, perform the tasks described in the following sections. The task in the first section is required; the tasks in the remaining sections are optional. For configuration examples, see the “Policy-Based Routing Configuration Examples” section.
- Enabling PBR (Required)
- Enabling Local PBR (Optional)
Enabling PBR
To enable PBR, you must create a route map that specifies the match criteria and the resulting action if all of the match clauses are met. Then you must apply that route-map on a particular interface. All packets arriving on the specified interface matching the match clauses are subject to PBR.
To enable PBR on an interface, perform this task:
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Switch(config)# route-map map-tag [ permit | deny ] [ sequence-number ] |
Defines a route map to control where packets are sent. This command puts the switch into route-map configuration mode. |
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Switch(config-route-map)# match ip address { access-list-number | name } [...access-list-number | name ] |
Specifies the match criteria. The match criteria take the form of one or more Standard or Extended IP access-lists. The access-lists can specify the source and destination IP addresses, protocol types, and port numbers. See Chapter 1, “Configuring Network Security with ACLs” for more information on Standard and Extended IP access-lists. |
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Switch(config-route-map)# set ip next-hop ip-address [... ip-address ] |
Specifies the next-hop IP address to which matching packets are sent. The next-hop IP address specified here must belong to a subnet that is directly connected to this switch. If more than one next-hop IP address is specified, the first usable next-hop is chosen for routing matching packets. If the next-hop is (or becomes) unavailable for some reason, the next one in the list is chosen. |
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Switch(config-route-map)# set ip next-hop recursive ip-address |
Specifies a recursive next-hop IP address. Note The recursive next-hop can be a subnet that is not directly connected. The set ip next-hop recursive command does not ensure that packets are routed through the recursive-next-hop if there is an intermediate node with a shorter route to the destination such that the route does not pass through the recursive-next-hop. |
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Switch(config-route-map)# set interface interface-type interface-number |
Specifies the output interface from which the packet will be sent. This action specifies that the packet is forwarded out of the local interface. The interface must be a Layer 3 interface (not a switchport). Packets are forwarded on the specified interface only if one of the following conditions is met:
If the destination IP address on the packet does not meet either of these conditions, the packet is dropped. This action forces matching packets to be switched in software.k |
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Switch(config-route-map)# set ip default next-hop ip-address [... ip-address ] |
Sets next hop to which to route the packet if there is no explicit route for the destination IP address in the packet. Before forwarding the packet to the next hop, the switch looks up the packet’s destination address in the unicast routing table. If a match is found, the packet is forwarded by way of the routing table. If no match is found, the packet is forwarded to the specified next hop. |
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Switch(config-route-map)# set default interface interface-type interface-number [... type...number ] |
Specifies the output interface from which the packet will be sent if there is no explicit route for this destination. Before forwarding the packet to the next hop, the switch looks up the packet’s destination address in the unicast routing table. If a match is found, the packet is forwarded by using the routing table. If no match is found, the packet is forwarded to the specified output interface. Packets are forwarded on the specified interface only if one of the following conditions is met:
If the destination IP address on the packet does not meet either of these conditions, the packet is dropped. This action forces matching packets to be switched in software. |
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Switch(config-route-map)# interface interface-type interface-number |
Specifies the interface. This command puts the switch into interface configuration mode. |
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Identifies the route map to use for PBR. One interface can only have one route map tag, but you can have multiple route map entries with different sequence numbers. These entries are evaluated in sequence number order until the first match. If no match exists, packets are routed as usual. |
Use the set commands with each other. These commands are evaluated in the order shown in Step 3 in the previous task table. A usable next hop implies an interface. Once the local switch finds a next hop and a usable interface, it routes the packet.
Use the show route-map map-tag command to display the existing route map.
Note Packet and byte counters in the output of the show route-map map-tag command are not updated.
Enabling Local PBR
Packets that are generated by the switch are not normally policy-routed. To enable local PBR for such packets, indicate which route map the switch should use by entering this command:
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All packets originating on the switch are then subject to local PBR.
Use the show ip local policy command to display the route map used for local PBR, if one exists.
Unsupported Commands
The following PBR commands in config-route-map mode are in the CLI but not supported in Cisco IOS for the Catalyst 4500 series switches. If you attempt to use these commands, an error message displays:
Policy-Based Routing Configuration Examples
The following sections provide PBR configuration examples:
For information on how to configure policy-based routing, see the section “Policy-Based Routing Configuration Tasks” in this chapter.
Equal Access
The following example provides two sources with equal access to two different service providers. Packets arriving on interface fastethernet 3/1 from the source 1.1.1.1 are sent to the switch at 6.6.6.6 if the switch has no explicit route for the destination of the packet. Packets arriving from the source 2.2.2.2 are sent to the switch at 7.7.7.7 if the switch has no explicit route for the destination of the packet. All other packets for which the switch has no explicit route to the destination are discarded.
Note If the packets you want to drop do not match either of the first two route-map clauses, then change |
set default interface null0 to set interface null0.
Differing Next Hops
The following example illustrates how to route traffic from different sources to different places (next hops). Packets arriving from source 1.1.1.1 are sent to the next hop at 3.3.3.3; packets arriving from source 2.2.2.2 are sent to the next hop at 3.3.3.5.
Deny ACE
The following example illustrates how to stop processing a given route map sequence, and to jump to the next sequence. Packets arriving from source 1.1.1.1 skip sequence 10 and jump to sequence 20. All other packets from subnet 1.1.1.0 follow the set statement in sequence 10.
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