Cisco IOS IPv6 Command Reference

mpls traffic-eng auto-bw timers

To enable automatic bandwidth adjustment for a platform and to start output rate sampling for tunnels configured for automatic bandwidth adjustment, use the mpls traffic-eng auto-bw timers command in global configuration mode. To disable automatic bandwidth adjustment for the platform, use the no form of this command.

mpls traffic-eng auto-bw timers [frequency seconds]

no mpls traffic-eng auto-bw timers

Syntax Description

Command Default

When the optional frequency keyword is not specified, the sampling interval is 300 seconds (5 minutes).

Command Modes

Global configuration

Command History

Usage Guidelines

The mpls traffic-eng auto-bw timers command enables automatic bandwidth adjustment on a platform by causing traffic engineering to periodically sample the output rate for each tunnel configured for bandwidth adjustment.

The no mpls traffic-eng auto-bw timers command disables automatic bandwidth adjustment for a platform by terminating the output rate sampling and bandwidth adjustment for tunnels configured for adjustment. In addition, the no form of the command restores the configured bandwidth for each tunnel where "configured bandwidth" is determined as follows:

•If the tunnel bandwidth was explicitly configured via the tunnel mpls traffic-eng bandwidth command after the running configuration was written (if at all) to the startup configuration, the "configured bandwidth" is the bandwidth specified by that command.

•Otherwise, the "configured bandwidth" is the bandwidth specified for the tunnel in the startup configuration.

Examples

The following example shows how to designate that for each Multiprotocol Label Switching (MPLS) traffic engineering tunnel, the output rate is sampled once every 10 minutes (every 600 seconds):

Router(config)# mpls traffic-eng auto-bw timers frequency 600

Related Commands

multi-topology

To enable multitopology Intermediate System-to-Intermediate System (IS-IS) for IPv6, use the multi-topology command in address family configuration mode. To disable multitopology IS-IS for IPv6, use the no form of this command.

multi-topology [transition]

no multi-topology

Syntax Description

Command Default

Multitopology IS-IS is disabled by default.

Command Modes

Address family configuration

Command History

Usage Guidelines

By default, the router runs IS-IS IPv6 in single SPF mode. The multi-topology command enables multitopology IS-IS for IPv6.

The optional transition keyword can be used to migrate from IS-IS IPv6 single SPF mode to multitopology IS-IS IPv6. When transition mode is enabled, the router advertises both multitopology type, length, and value (TLV) objects and single-SPF-mode IS-IS IPv6 TLVs, but the SPF is computed using the single-SPF-mode IS-IS IPv6 TLV. This action has the side effect of increasing the link-state packet (LSP) size.

Examples

The following example enables multitopology IS-IS for IPv6:

Router(config)# router isis

Router(config-router)# address-family ipv6

Router(config-router-af)# multi-topology

nai

To specify the network address identifier (NAI) for the IPv6 mobile node, use the nai command in home agent configuration mode or IPv6 mobile router host configuration mode. To remove a host configuration, use the no form of this command.

nai [realm | user | macaddress] {user@realm | @realm}

no nai

Syntax Description

Command Default

No NAI is specified.

Command Modes

Home agent configuration (config-ha)
IPv6 mobile router host configuration (IPv6-mobile-router-host-config)

Command History

Usage Guidelines

The nai command can be used to configure a specific user NAI or a generic realm for defining a group.

When the address command is configured with a specific IPv6 address, the nai command cannot be configured using the @realm argument. For example, the following nai command configuration would not be valid because the address command is configured with the specific address baba::1:

host group group1

  nai  @cisco.com

  address baba::1

Two different profiles cannot be configured with the nai command configured with the same @realm value. For example, the following two profiles are configured with the same NAI realm of @cisco.com, which is not valid:

host group group1

  nai  @cisco.com

host group group2

  nai  @cisco.com

However, if the one of the profiles uses a fully qualified NAI, which is configured using the nai command with the user@realm argument, its properties take precedence over the group profile for that user, and the second group's configuration using the nai command with the @realm argument is valid.

host group group1

  nai example@cisco.com

host group group2

  nai  @cisco.com 

Examples

In the following example, the host group named group1 is configured using the NAI fully qualified realm of example@cisco.com:

host group group1

  nai example@cisco.com

Related Commands

neighbor (EIGRP)

To define a neighboring router with which to exchange routing information on a router that is running Enhanced Interior Gateway Routing Protocol (EIGRP), use the neighbor command in router configuration mode or address-family configuration mode. To remove an entry, use the no form of this command.

neighbor {ip-address | ipv6-address} interface-type interface-number [remote maximum-hops]

no neighbor {ip-address | ipv6-address} interface-type interface-number

Syntax Description

Command Default

No neighboring routers are defined.

Command Modes

Router configuration (config-router)
Address-family configuration (config-router-af)

Command History

Usage Guidelines

Multiple neighbor statements can be used to establish peering sessions with specific EIGRP neighbors. The interface through which EIGRP will exchange routing updates must be specified in the neighbor statement. The interfaces through which two EIGRP neighbors exchange routing updates must be configured with IP addresses from the same network.

Note Configuring the passive-interface command suppresses all incoming and outgoing routing updates and hello messages. EIGRP neighbor adjacencies cannot be established or maintained over an interface that is configured as passive.

Examples

The following example configures EIGRP peering sessions with the 192.168.1.1 and 192.168.2.2 neighbors:

Router(config)# router eigrp 1

Router(config-router)# network 192.168.0.0

Router(config-router)# neighbor 192.168.1.1 Ethernet 0/0

Router(config-router)# neighbor 192.168.2.2 Ethernet 1/1

The following named configuration example configures EIGRP to send address-family updates to specific neighbors:

Router(config)# router eigrp virtual-name

Router(config-router)# address-family ipv4 autonomous-system 4453

Router(config-router-af)# neighbor 192.168.1.1 ethernet0/0

Router(config-router-af)# neighbor 10.1.1.2 loopback0 remote 10

Related Commands

neighbor activate

To enable the exchange of information with a Border Gateway Protocol (BGP) neighbor, use the neighbor activate command in address family configuration mode or router configuration mode. To disable the exchange of an address with a BGP neighbor, use the no form of this command.

neighbor {ip-address | peer-group-name | ipv6-address%} activate

no neighbor {ip-address | peer-group-name | ipv6-address%} activate

Syntax Description

Command Default

The exchange of addresses with BGP neighbors is enabled for the IPv4 address family. Enabling address exchange for all other address families is disabled.

Note Address exchange for address family IPv4 is enabled by default for each BGP routing session configured with the neighbor remote-as command unless you configure the no bgp default ipv4-activate command before configuring the neighbor remote-as command, or you disable address exchange for address family IPv4 with a specific neighbor by using the no form of the neighbor activate command.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

Use this command to advertise address information in the form of an IP or IPv6 prefix. The address prefix information is known as Network Layer Reachability Information (NLRI) in BGP.

The % keyword is used whenever link-local IPv6 addresses are used outside the context of their interfaces. This keyword does not need to be used for non-link-local IPv6 addresses.

Examples

Address Exchange Example for Address Family vpn4

The following example shows how to enable address exchange for address family vpnv4 for all neighbors in the BGP peer group named PEPEER and for the neighbor 10.0.0.44:

Router(config)# address-family vpnv4

Router(config-router-af)# neighbor PEPEER activate

Router(config-router-af)# neighbor 10.0.0.44 activate

Router(config-router-af)# exit-address-family

Address Exchange Example for Address Family IPv4 Unicast

The following example shows how to enable address exchange for address family IPv4 unicast for all neighbors in the BGP peer group named group1 and for the BGP neighbor 172.16.1.1:

Router(config)# address-family ipv4 unicast

Router(config-router-af)# neighbor group1 activate

Router(config-router-af)# neighbor 172.16.1.1 activate

Address Exchange Example for Address Family IPv6

The following example shows how to enable address exchange for address family IPv6 for all neighbors in the BGP peer group named group2 and for the BGP neighbor 7000::2:

Router(config)# address-family ipv6

Router(config-router-af)# neighbor group2 activate

Router(config-router-af)# neighbor 7000::2 activate

Related Commands

neighbor ebgp-multihop

To accept and attempt BGP connections to external peers residing on networks that are not directly connected, use the neighbor ebgp-multihop command in router configuration mode. To return to the default, use the no form of this command.

neighbor {ip-address | ipv6-address | peer-group-name} ebgp-multihop [ttl]

no neighbor {ip-address | ipv6-address | peer-group-name} ebgp-multihop

Syntax Description

Command Default

Only directly connected neighbors are allowed.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

This feature should be used only under the guidance of Cisco technical support staff.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

To prevent the creation of loops through oscillating routes, the multihop will not be established if the only route to the multihop peer is the default route (0.0.0.0).

Examples

The following example allows connections to or from neighbor 10.108.1.1, which resides on a network that is not directly connected:

router bgp 109

 neighbor 10.108.1.1 ebgp-multihop

Related Commands

neighbor next-hop-unchanged

To enable an external BGP (eBGP) peer that is configured as multihop to propagate the next hop unchanged, use the neighbor next-hop-unchanged command in address family or router configuration mode. To disable that propagation of the next hop being unchanged, use the no form of this command.

neighbor {ip-address | ipv6-address | peer-group-name} next-hop-unchanged [allpaths]

no neighbor {ip-address | ipv6-address | peer-group-name} next-hop-unchanged [allpaths]

Syntax Description

Command Default

This command is disabled by default.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

By default, for eBGP, the next hop to reach a connected network is the IP address of the neighbor that sent the update. Therefore, as an update goes from router to router, the next hop typically changes to be the address of the neighbor that sent the update (the router's own address).

However, there might be a scenario where you want the next hop to remain unchanged. The neighbor next-hop-unchanged command is used to propagate the next hop unchanged for multihop eBGP peering sessions. This command is configured on an eBGP neighbor, but the neighbor propagates routes learned from iBGP; that is, the neighbor propagates the next hop of iBGP routes toward eBGP.

Caution Using the neighbor next-hop-unchanged command or incorrectly altering the BGP next hop can cause inconsistent routing, routing loops, or a loss of connectivity. It should only be attempted by someone who has a good understanding of the design implications.

This command can be used to configure MPLS VPNs between service providers by not modifying the next hop attribute when advertising routes to an eBGP peer.

Examples

The following example configures a multihop eBGP peer at 10.0.0.100 in a remote autonomous system (AS). When the local router sends updates to that peer, it will send them without modifying the next hop attribute.

router bgp 65535

 address-family ipv4

 neighbor 10.0.0.100 remote-as 65600

 neighbor 10.0.0.100 activate 

 neighbor 10.0.0.100 ebgp-multihop 255

 neighbor 10.0.0.100 next-hop-unchanged

 end

Related Commands

neighbor override-capability-neg

To enable the IPv6 address family for a Border Gateway Protocol (BGP) neighbor that does not support capability negotiation, use the neighbor override-capability-neg command in address family configuration mode. To disable the IPv6 address family for a BGP neighbor that does not support capability negotiation, use the no form of this command.

neighbor {peer-group-name | ipv6-address} override-capability-neg

no neighbor {peer-group-name | ipv6-address} override-capability-neg

Syntax Description

Command Default

Capability negotiation is enabled.

Command Modes

Address family configuration

Command History

Usage Guidelines

Capability negotiation is used to establish a connection between BGP-speaking peers. If one of the BGP peers does not support capability negotiation, the connection is automatically terminated. The neighbor override-capability-neg command overrides the capability negotiation process and enables BGP-speaking peers to establish a connection.

The neighbor override-capability-neg command is supported only in address family configuration mode for the IPv6 address family.

Examples

The following example enables the IPv6 address family for BGP neighbor 7000::2:

Router(config)# address-family ipv6

Router(config-router-af)# neighbor 7000::2 override-capability-neg

The following example enables the IPv6 address family for all neighbors in the BGP peer group named group1:

Router(config)# address-family ipv6

Router(config-router-af)# neighbor group1 override-capability-neg

Related Commands

neighbor peer-group (assigning members)

To configure a BGP neighbor to be a member of a peer group, use the neighbor peer-group command in address family or router configuration mode. To remove the neighbor from the peer group, use the no form of this command.

neighbor {ip-address | ipv6-address} peer-group peer-group-name

no neighbor {ip-address | ipv6-address} peer-group peer-group-name

Syntax Description

Defaults

There are no BGP neighbors in a peer group.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

The neighbor at the IP address indicated inherits all the configured options of the peer group.

Note Using the no form of the neighbor peer-group command removes all of the BGP configuration for that neighbor, not just the peer group association.

Examples

The following router configuration mode example assigns three neighbors to the peer group named internal:

router bgp 100

 neighbor internal peer-group

 neighbor internal remote-as 100

 neighbor internal update-source loopback 0

 neighbor internal route-map set-med out

 neighbor internal filter-list 1 out

 neighbor internal filter-list 2 in

 neighbor 172.16.232.53 peer-group internal

 neighbor 172.16.232.54 peer-group internal

 neighbor 172.16.232.55 peer-group internal

 neighbor 172.16.232.55 filter-list 3 in

The following address family configuration mode example assigns three neighbors to the peer group named internal:

router bgp 100

address-family ipv4 unicast

 neighbor internal peer-group

 neighbor internal remote-as 100

 neighbor internal update-source loopback 0

 neighbor internal route-map set-med out

 neighbor internal filter-list 1 out

 neighbor internal filter-list 2 in

 neighbor 172.16.232.53 peer-group internal

 neighbor 172.16.232.54 peer-group internal

 neighbor 172.16.232.55 peer-group internal

 neighbor 172.16.232.55 filter-list 3 in

Related Commands

neighbor peer-group (creating)

To create a BGP or multiprotocol BGP peer group, use the neighbor peer-group command in address family or router configuration mode. To remove the peer group and all of its members, use the no form of this command.

neighbor peer-group-name peer-group

no neighbor peer-group-name peer-group

Syntax Description

Defaults

There is no BGP peer group.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

Often in a BGP or multiprotocol BGP speaker, many neighbors are configured with the same update policies (that is, same outbound route maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be grouped into peer groups to simplify configuration and make update calculation more efficient.

Note Peer group members can span multiple logical IP subnets, and can transmit, or pass along, routes from one peer group member to another.

Once a peer group is created with the neighbor peer-group command, it can be configured with the neighbor commands. By default, members of the peer group inherit all the configuration options of the peer group. Members also can be configured to override the options that do not affect outbound updates.

All the peer group members will inherit the current configuration as well as changes made to the peer group. Peer group members will always inherit the following configuration options by default:

•remote-as (if configured)

•version

•update-source

•outbound route-maps

•outbound filter-lists

•outbound distribute-lists

•minimum-advertisement-interval

•next-hop-self

If a peer group is not configured with a remote-as option, the members can be configured with the neighbor {ip-address | peer-group-name} remote-as command. This command allows you to create peer groups containing external BGP (eBGP) neighbors.

Examples

The following example configurations show how to create these types of neighbor peer group:

•internal Border Gateway Protocol (iBGP) peer group

•eBGP peer group

•Multiprotocol BGP peer group

iBGP Peer Group

In the following example, the peer group named internal configures the members of the peer group to be iBGP neighbors. By definition, this is an iBGP peer group because the router bgp command and the neighbor remote-as command indicate the same autonomous system (in this case, autonomous system 100). All the peer group members use loopback 0 as the update source and use set-med as the outbound route map. The neighbor internal filter-list 2 in command shows that, except for 172.16.232.55, all the neighbors have filter list 2 as the inbound filter list.

router bgp 100

 neighbor internal peer-group

 neighbor internal remote-as 100

 neighbor internal update-source loopback 0

 neighbor internal route-map set-med out

 neighbor internal filter-list 1 out

 neighbor internal filter-list 2 in

 neighbor 172.16.232.53 peer-group internal

 neighbor 172.16.232.54 peer-group internal

 neighbor 172.16.232.55 peer-group internal

 neighbor 172.16.232.55 filter-list 3 in

eBGP Peer Group

The following example defines the peer group named external-peers without the neighbor remote-as command. By definition, this is an eBGP peer group because each individual member of the peer group is configured with its respective autonomous system number separately. Thus the peer group consists of members from autonomous systems 200, 300, and 400. All the peer group members have the set-metric route map as an outbound route map and filter list 99 as an outbound filter list. Except for neighbor 172.16.232.110, all of them have 101 as the inbound filter list.

router bgp 100

 neighbor external-peers peer-group

 neighbor external-peers route-map set-metric out

 neighbor external-peers filter-list 99 out

 neighbor external-peers filter-list 101 in

 neighbor 172.16.232.90 remote-as 200

 neighbor 172.16.232.90 peer-group external-peers

 neighbor 172.16.232.100 remote-as 300

 neighbor 172.16.232.100 peer-group external-peers

 neighbor 172.16.232.110 remote-as 400

 neighbor 172.16.232.110 peer-group external-peers

 neighbor 172.16.232.110 filter-list 400 in

Multiprotocol BGP Peer Group

In the following example, all members of the peer group are multicast-capable:

router bgp 100

neighbor 10.1.1.1 remote-as 1

neighbor 172.16.2.2 remote-as 2

address-family ipv4 multicast

 neighbor mygroup peer-group

 neighbor 10.1.1.1 peer-group mygroup

 neighbor 172.16.2.2 peer-group mygroup

 neighbor 10.1.1.1 activate

 neighbor 172.16.2.2 activate

Related Commands

neighbor remote-as

To add an entry to the BGP or multiprotocol BGP neighbor table, use the neighbor remote-as command in router configuration mode. To remove an entry from the table, use the no form of this command.

neighbor {ip-address | ipv6-address[%] | peer-group-name} remote-as autonomous-system-number [alternate-as autonomous-system-number ...]

no neighbor {ip-address | ipv6-address[%] | peer-group-name} remote-as autonomous-system-number [alternate-as autonomous-system-number ...]

Syntax Description

Command Default

There are no BGP or multiprotocol BGP neighbor peers.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

Specifying a neighbor with an autonomous system number that matches the autonomous system number specified in the router bgp global configuration command identifies the neighbor as internal to the local autonomous system. Otherwise, the neighbor is considered external.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

By default, neighbors that are defined using the neighbor remote-as command in router configuration mode exchange only unicast address prefixes. To exchange other address prefix types, such as multicast and Virtual Private Network (VPN) Version 4, neighbors must also be activated in the appropriate address family configuration mode.

Use the alternate-as keyword introduced in Cisco IOS Release 12.2(33)SXH to specify up to five alternate autonomous systems in which a dynamic BGP neighbor may be identified. BGP dynamic neighbor support allows BGP peering to a group of remote neighbors that are defined by a range of IP addresses. BGP dynamic neighbors are configured using a range of IP addresses and BGP peer groups. After a subnet range is configured and associated with a BGP peer group using the bgp listen command and a TCP session is initiated for an IP address in the subnet range, a new BGP neighbor is dynamically created as a member of that group. The new BGP neighbor will inherit any configuration or templates for the group.

The % keyword is used whenever link-local IPv6 addresses are used outside the context of their interfaces. This keyword does not need to be used for non-link-local IPv6 addresses.

In Cisco IOS Release 12.0(32)SY8, 12.0(33)S3, 12.2(33)SRE, 12.2(33)XNE, 12.2(33)SXI1, Cisco IOS XE Release 2.4, and later releases, the Cisco implementation of 4-byte autonomous system numbers uses asplain—65538 for example—as the default regular expression match and output display format for autonomous system numbers, but you can configure 4-byte autonomous system numbers in both the asplain format and the asdot format as described in RFC 5396. To change the default regular expression match and output display of 4-byte autonomous system numbers to asdot format, use the bgp asnotation dot command followed by the clear ip bgp * command to perform a hard reset of all current BGP sessions.

In Cisco IOS Release 12.0(32)S12, 12.4(24)T, and Cisco IOS XE Release 2.3, the Cisco implementation of 4-byte autonomous system numbers uses asdot—1.2 for example—as the only configuration format, regular expression match, and output display, with no asplain support.

Note In Cisco IOS releases that include 4-byte ASN support, command accounting and command authorization that include a 4-byte ASN number are sent in the asplain notation irrespective of the format that is used on the command-line interface.

To ensure a smooth transition, we recommend that all BGP speakers within an autonomous system that is identified using a 4-byte autonomous system number, be upgraded to support 4-byte autonomous system numbers.

Examples

The following example specifies that a router at the address 10.108.1.2 is an internal BGP (iBGP) neighbor in autonomous system number 65200:

router bgp 65200

 network 10.108.0.0

 neighbor 10.108.1.2 remote-as 65200

The following example specifies that a router at the IPv6 address 2001:0DB8:1:1000::72a is an external BGP (eBGP) neighbor in autonomous system number 65001:

router bgp 65300

 address-family ipv6 vrf site1

 neighbor 2001:0DB8:1:1000::72a remote-as 65001

The following example assigns a BGP router to autonomous system 65400, and two networks are listed as originating in the autonomous system. Then the addresses of three remote routers (and their autonomous systems) are listed. The router being configured will share information about networks 10.108.0.0 and 192.168.7.0 with the neighbor routers. The first router is a remote router in a different autonomous system from the router on which this configuration is entered (an eBGP neighbor); the second neighbor remote-as command shows an internal BGP neighbor (with the same autonomous system number) at address 10.108.234.2; and the last neighbor remote-as command specifies a neighbor on a different network from the router on which this configuration is entered (also an eBGP neighbor).

router bgp 65400

 network 10.108.0.0

 network 192.168.7.0

 neighbor 10.108.200.1 remote-as 65200

 neighbor 10.108.234.2 remote-as 65400

 neighbor 172.29.64.19 remote-as 65300

The following example configures neighbor 10.108.1.1 in autonomous system 65001 to exchange only multicast routes:

router bgp 65001

 neighbor 10.108.1.1 remote-as 65001

 neighbor 172.31 1.2 remote-as 65001

 neighbor 172.16.2.2 remote-as 65002

 address-family ipv4 multicast

  neighbor 10.108.1.1 activate

  neighbor 172.31 1.2 activate

  neighbor 172.16.2.2 activate

  exit-address-family

The following example configures neighbor 10.108.1.1 in autonomous system 65001 to exchange only unicast routes:

router bgp 65001

 neighbor 10.108.1.1 remote-as 65001

 neighbor 172.31 1.2 remote-as 65001

 neighbor 172.16.2.2 remote-as 65002

The following example, configurable only in Cisco IOS Release 12.2(33)SXH and later releases, configures a subnet range of 192.168.0.0/16 and associates this listen range with a BGP peer group. Note that the listen range peer group that is configured for the BGP dynamic neighbor feature can be activated in the IPv4 address family using the neighbor activate command. After the initial configuration on Router 1, when Router 2 starts a BGP router session and adds Router 1 to its BGP neighbor table, a TCP session is initiated, and Router 1 creates a new BGP neighbor dynamically because the IP address of the new neighbor is within the listen range subnet.

Router 1

enable

configure terminal

router bgp 45000

 bgp log-neighbor-changes

 neighbor group192 peer-group 

 bgp listen range 192.168.0.0/16 peer-group group192   

 neighbor group192 remote-as 40000 alternate-as 50000

 address-family ipv4 unicast 

 neighbor group192 activate

 end

Router 2

enable

configure terminal

router bgp 50000

 neighbor 192.168.3.1 remote-as 45000

 exit

If the show ip bgp summary command is now entered on Router 1, the output shows the dynamically created BGP neighbor, 192.168.3.2.

Router1# show ip bgp summary

BGP router identifier 192.168.3.1, local AS number 45000

BGP table version is 1, main routing table version 1

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd

*192.168.3.2    4 50000       2       2        0    0    0 00:00:37        0

* Dynamically created based on a listen range command

Dynamically created neighbors: 1/(200 max), Subnet ranges: 1

BGP peergroup group192 listen range group members: 

  192.168.0.0/16 

The following example configures a BGP process for autonomous system 65538 and configures two external BGP neighbors in different autonomous systems using 4-byte autonomous system numbers in asplain format. This example is supported only on Cisco IOS Release 12.0(32)SY8, 12.0(33)S3, 12.2(33)SRE, 12.2(33)XNE, 12.2(33)SXI1, Cisco IOS XE Release 2.4, or later releases.

router bgp 65538

 neighbor 192.168.1.2 remote-as 65536

 neighbor 192.168.3.2 remote-as 65550

 neighbor 192.168.3.2 description finance

 !

 address-family ipv4

  neighbor 192.168.1.2 activate

  neighbor 192.168.3.2 activate

  no auto-summary

  no synchronization

  network 172.17.1.0 mask 255.255.255.0

  exit-address-family

The following example configures a BGP process for autonomous system 1.2 and configures two external BGP neighbors in different autonomous systems using 4-byte autonomous system numbers in asdot format. This example requires Cisco IOS Release 12.0(32)SY8, 12.0(32)S12, 12.2(33)SRE, 12.2(33)XNE, 12.2(33)SXI1, 12.4(24)T, Cisco IOS XE Release 2.3, or a later release.

router bgp 1.2

 neighbor 192.168.1.2 remote-as 1.0

 neighbor 192.168.3.2 remote-as 1.14

 neighbor 192.168.3.2 description finance

 !

 address-family ipv4

  neighbor 192.168.1.2 activate

  neighbor 192.168.3.2 activate

  no auto-summary

  no synchronization

  network 172.17.1.0 mask 255.255.255.0

  exit-address-family

Related Commands

neighbor route-map

To apply a route map to incoming or outgoing routes, use the neighbor route-map command in address family or router configuration mode. To remove a route map, use the no form of this command.

neighbor {ip-address | peer-group-name | ipv6-address [%]} route-map map-name {in | out}

no neighbor {ip-address | peer-group-name | ipv6-address [%]} route-map map-name {in | out}

Syntax Description

Command Default

No route maps are applied to a peer.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

When specified in address family configuration mode, this command applies a route map to that particular address family only. When specified in router configuration mode, this command applies a route map to IPv4 or IPv6 unicast routes only.

If an outbound route map is specified, it is proper behavior to only advertise routes that match at least one section of the route map.

If you specify a BGP or multiprotocol BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command. Specifying the command for a neighbor overrides the inbound policy that is inherited from the peer group.

The % keyword is used whenever link-local IPv6 addresses are used outside the context of their interfaces. This keyword does not need to be used for non-link-local IPv6 addresses.

Examples

The following router configuration mode example applies a route map named internal-map to a BGP incoming route from 172.16.70.24:

router bgp 5

 neighbor 172.16.70.24 route-map internal-map in

route-map internal-map

 match as-path 1

 set local-preference 100

The following address family configuration mode example applies a route map named internal-map to a multiprotocol BGP incoming route from 172.16.70.24:

router bgp 5

address-family ipv4 multicast

 neighbor 172.16.70.24 route-map internal-map in

route-map internal-map

 match as-path 1

 set local-preference 100

Related Commands

neighbor route-reflector-client

To configure the router as a BGP route reflector and configure the specified neighbor as its client, use the neighbor route-reflector-client command in address family or router configuration mode. To indicate that the neighbor is not a client, use the no form of this command.

neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client

no neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client

Syntax Description

Command Default

There is no route reflector in the autonomous system.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

By default, all internal BGP (iBGP) speakers in an autonomous system must be fully meshed, and neighbors do not readvertise iBGP learned routes to neighbors, thus preventing a routing information loop. When all the clients are disabled, the local router is no longer a route reflector.

If you use route reflectors, all iBGP speakers need not be fully meshed. In the route reflector model, an Interior BGP peer is configured to be a route reflector responsible for passing iBGP learned routes to iBGP neighbors. This scheme eliminates the need for each router to talk to every other router.

Use the neighbor route-reflector-client command to configure the local router as the route reflector and the specified neighbor as one of its clients. All the neighbors configured with this command will be members of the client group and the remaining iBGP peers will be members of the nonclient group for the local route reflector.

The bgp client-to-client reflection command controls client-to-client reflection.

Examples

In the following router configuration mode example, the local router is a route reflector. It passes learned iBGP routes to the neighbor at 172.16.70.24.

router bgp 5

 neighbor 172.16.70.24 route-reflector-client

In the following address family configuration mode example, the local router is a route reflector. It passes learned iBGP routes to the neighbor at 172.16.70.24.

router bgp 5

address-family ipv4 unicast

 neighbor 172.16.70.24 route-reflector-client

Related Commands

neighbor send-community

To specify that a communities attribute should be sent to a BGP neighbor, use the neighbor send-community command in address family or router configuration mode. To remove the entry, use the no form of this command.

neighbor {ip-address | ipv6-address | peer-group-name} send-community [both | standard | extended]

no neighbor {ip-address | ipv6-address | peer-group-name} send-community

Syntax Description

Command Default

No communities attribute is sent to any neighbor.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

Examples

In the following router configuration mode example, the router belongs to autonomous system 109 and is configured to send the communities attribute to its neighbor at IP address 172.16.70.23:

router bgp 109

 neighbor 172.16.70.23 send-community

In the following address family configuration mode example, the router belongs to autonomous system 109 and is configured to send the communities attribute to its neighbor at IP address 172.16.70.23:

router bgp 109

address-family ipv4 multicast

 neighbor 172.16.70.23 send-community

Related Commands

neighbor send-label

To enable a Border Gateway Protocol (BGP) router to send Multiprotocol Label Switching (MPLS) labels with BGP routes to a neighboring BGP router, use the neighbor send-label command in address family configuration mode or router configuration mode. To disable this feature, use the no form of this command.

neighbor {ip-address | ipv6-address | peer-group-name} send-label [explicit-null]

neighbor {ip-address | ipv6-address | peer-group-name} send-label [explicit-null]

Syntax Description

Command Default

BGP routers distribute only BGP routes.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

The neighbor send-label command enables a router to use BGP to distribute MPLS labels along with IPv4 routes to a peer router. You must issue this command on both the local and the neighboring router.

This command has the following restrictions:

•If a BGP session is running when you issue the neighbor send-label command, the BGP session flaps immediately after the command is issued.

•In router configuration mode, only IPv4 addresses are distributed.

Use the neighbor send-label command in address family configuration mode, to bind and advertise IPv6 prefix MPLS labels. Using this command in conjunction with the mpls ipv6 source-interface global configuration command allows IPv6 traffic to run over an IPv4 MPLS network without any software or hardware configuration changes in the backbone. Edge routers configured to run both IPv4 and IPv6 traffic forward IPv6 traffic using MPLS and multiprotocol internal BGP (MP-iBGP).

Cisco IOS software installs /32 routes for directly connected external BGP (eBGP) peers when the BGP session for such a peer comes up. The /32 routes are installed only when MPLS labels are exchanged between such peers. Directly connected eBGP peers exchange MPLS labels for:

•IP address families (IPv4 and IPv6) with the neighbor send-label command enabled for the peers

•VPN address families (VPNv4 and VPNv6)

A single BGP session can include multiple address families. If one of the families exchanges MPLS labels, the /32 neighbor route is installed for the connected peer.

Examples

The following example shows how to enable a router in autonomous system 65000 to send MPLS labels with BGP routes to the neighboring BGP router at 192.168.0.1:

Router(config)# router bgp 65000

Router(config-router)# neighbor 192.168.0.1 remote-as 65001

Router(config-router)# neighbor 192.168.0.1 send-label

The following example shows how to enable a router in the autonomous system 65000 to bind and advertise IPv6 prefix MPLS labels and send the labels with BGP routes to the neighboring BGP router at 192.168.99.70:

Router(config)# router bgp 65000

Router(config-router)# neighbor 192.168.99.70 remote-as 65000

Router(config-router)# address-family ipv6

Router(config-router-af)# neighbor 192.168.99.70 activate

Router(config-router-af)# neighbor 192.168.99.70 send-label

Related Commands

neighbor translate-update

To generate multiprotocol IPv6 Border Gateway Protocol (BGP) updates that correspond to unicast IPv6 updates received from a peer, use the neighbor translate-update command in address family or router configuration mode. To return to default values, use the no form of the command.

neighbor ipv6-address translate-update ipv6 multicast [unicast]

no neighbor ipv6-address translate-update ipv6 multicast [unicast]

Syntax Description

Command Default

No BGP updates for unicast IPv6 are updated

Command Modes

Address family configuration
Router configuration

Command History

Usage Guidelines

The multicast BGP (MBGP) translate-update feature generally is used in an MBGP-capable router that peers with a customer site that has a router that is only BGP capable; the customer site has not or cannot upgrade the router to an MBGP-capable image. Because the customer site cannot originate MBGP advertisements, the router with which it peers will translate the BGP prefixes into MBGP prefixes, which are used for multicast-source Reverse Path Forwarding (RPF) lookup.

Examples

The following example generates multiprotocol IPv6 BGP updates that correspond to unicast IPv6 updates received from peer at address 7000::2:

neighbor 7000::2 translate-update ipv6 multicast 

neighbor update-source

To have the Cisco IOS software allow Border Gateway Protocol (BGP) sessions to use any operational interface for TCP connections, use the neighbor update-source command in router configuration mode. To restore the interface assignment to the closest interface, which is called the best local address, use the no form of this command.

neighbor {ip-address | ipv6-address[%] | peer-group-name} update-source interface-type interface-number

no neighbor {ip-address | ipv6-address[%] | peer-group-name} update-source interface-type interface-number

Syntax Description

Command Default

Best local address

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

This command can work in conjunction with the loopback interface feature described in the "Interface Configuration Overview" chapter of the Cisco IOS Interface and Hardware Component Configuration Guide.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command.

The neighbor update-source command must be used to enable IPv6 link-local peering for internal or external BGP sessions.

The % keyword is used whenever link-local IPv6 addresses are used outside the context of their interfaces and for these link-local IPv6 addresses you must specify the interface they are on. The syntax becomes <IPv6 local-link address>%<interface name>, for example, FE80::1%Ethernet1/0. Note that the interface type and number must not contain any spaces, and be used in full-length form because name shortening is not supported in this situation. The % keyword and subsequent interface syntax is not used for non-link-local IPv6 addresses.

Examples

The following example sources BGP TCP connections for the specified neighbor with the IP address of the loopback interface rather than the best local address:

router bgp 65000

 network 172.16.0.0

 neighbor 172.16.2.3 remote-as 110

 neighbor 172.16.2.3 update-source Loopback0

The following example sources IPv6 BGP TCP connections for the specified neighbor in autonomous system 65000 with the global IPv6 address of loopback interface 0 and the specified neighbor in autonomous system 65400 with the link-local IPv6 address of Fast Ethernet interface 0/0. Note that the link-local IPv6 address of FE80::2 is on Ethernet interface 1/0.

router bgp 65000

 neighbor 3ffe::3 remote-as 65000 

 neighbor 3ffe::3 update-source Loopback0 

 neighbor fe80::2%Ethernet1/0 remote-as 65400 

 neighbor fe80::2%Ethernet1/0 update-source FastEthernet 0/0 

 address-family ipv6 

  neighbor 3ffe::3 activate 

  neighbor fe80::2%Ethernet1/0 activate 

  exit-address-family 

Related Commands

network (BGP and multiprotocol BGP)

To specify the networks to be advertised by the Border Gateway Protocol (BGP) and multiprotocol BGP routing processes, use the network command in address family or router configuration mode. To remove an entry from the routing table, use the no form of this command.

network {network-number [mask network-mask] | nsap-prefix} [route-map map-tag]

no network {network-number [mask network-mask] | nsap-prefix} [route-map map-tag]

Syntax Description

Command Default

No networks are specified.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Usage Guidelines

BGP and multiprotocol BGP networks can be learned from connected routes, from dynamic routing, and from static route sources.

The maximum number of network commands you can use is determined by the resources of the router, such as the configured NVRAM or RAM.

Examples

The following example sets up network 10.108.0.0 to be included in the BGP updates:

router bgp 65100

 network 10.108.0.0

The following example sets up network 10.108.0.0 to be included in the multiprotocol BGP updates:

router bgp 64800

address family ipv4 multicast

 network 10.108.0.0

The following example advertises NSAP prefix 49.6001 in the multiprotocol BGP updates:

router bgp 64500

 address-family nsap

  network 49.6001

Related Commands

network (IPv6)

To configure the network source of the next hop to be used by the PE VPN, use the network command in router configuration mode. To disable the source, use the no form of this command.

network ipv6-address/prefix-length

no network ipv6-address/prefix-length

Syntax Description

Command Default

Next-hop network sources are not configured.

Command Modes

Address family configuration
Router configuration

Command History

Usage Guidelines

The ipv6-address argument in this command configures the IPv6 network number.

Examples

The following example places the router in address family configuration mode and configures the network source to be used as the next hop:

Router(config)# router bgp 100

Router(config-router)# network 2001:DB8:100::1/128

Related Commands

nis address

To specify the network information service (NIS) address of an IPv6 server to be sent to the client, use the nis address command in DHCP for IPv6 pool configuration mode. To remove the NIS address, use the no form of this command.

nis address ipv6-address

no nis address ipv6-address

Syntax Description

Command Default

No NIS address is specified.

Command Modes

IPv6 DHCP pool configuration

Command History

Usage Guidelines

The Dynamic Host Configuration Protocol (DHCP) for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.

The NIS server option provides a list of one or more IPv6 addresses of NIS servers available to send to the client. The client must view the list of NIS servers as an ordered list, and the server may list the NIS servers in the order of the server's preference.

The NIS server option code is 27. For more information on DHCP options and suboptions, see the "DHCPv6 Options" appendix in the Network Registrar User's Guide, Release 6.2.

Examples

The following example shows how to specify the NIS address of an IPv6 server:

nis address 23::1

Related Commands

nis domain-name

To enable a server to convey a client's network information service (NIS) domain name information to the client, use the nis domain-name command in DHCP for IPv6 pool configuration mode. To remove the domain name, use the no form of this command.

nis domain-name domain-name

no nis domain-name domain-name

Syntax Description

Command Default

No NIS domain name is specified.

Command Modes

IPv6 DHCP pool configuration

Command History

Usage Guidelines

The Dynamic Host Configuration Protocol (DHCP) for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.

The NIS domain name option provides a NIS domain name for the client. Use the nis domain-name command to specify the client's NIS domain name that the server sends to the client.

The NIS domain name option code is 29. For more information on DHCP options and suboptions, see the "DHCPv6 Options" appendix in the Network Registrar User's Guide, Release 6.2.

Examples

The following example shows how to enable the IPv6 server to specify the NIS domain name of a client:

nis domain-name cisco1.com

Related Commands

nisp address

To specify the network information service plus (NIS+) address of an IPv6 server to be sent to the client, use the nisp address command in DHCP for IPv6 pool configuration mode. To remove the NIS+ address, use the no form of the command.

nisp address ipv6-address

no nisp address ipv6-address

Syntax Description

Command Default

No NIS+ address is specified.

Command Modes

IPv6 DHCP pool configuration

Command History

Usage Guidelines

The Dynamic Host Configuration Protocol (DHCP) for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.

The NIS+ servers option provides a list of one or more IPv6 addresses of NIS+ servers available to send to the client. The client must view the list of NIS+ servers as an ordered list, and the server may list the NIS+ servers in the order of the server's preference.

The NIS+ servers option code is 28. For more information on DHCP options and suboptions, see the "DHCPv6 Options" appendix in the Network Registrar User's Guide, Release 6.2.

Examples

The following example shows how to specify the NIS+ address of an IPv6 server:

nisp address 33::1

Related Commands

nisp domain-name

To enable an IPv6 server to convey a client's network information service plus (NIS+) domain name information to the client, use the nisp domain-name command in DHCP for IPv6 pool configuration mode. To remove the domain name, use the no form of this command.

nisp domain-name domain-name

no nisp domain-name domain-name

Syntax Description

Command Default

No NIS+ domain name is specified.

Command Modes

IPv6 DHCP pool configuration

Command History

Usage Guidelines

The Dynamic Host Configuration Protocol (DHCP) for IPv6 for stateless configuration allows a DHCP for IPv6 client to export configuration parameters (that is, DHCP for IPv6 options) to a local DHCP for IPv6 server pool. The local DHCP for IPv6 server can then provide the imported configuration parameters to other DHCP for IPv6 clients.

The NIS+ domain name option provides a NIS+ domain name for the client. Use the nisp domain-name command to enable a server to send the client its NIS+ domain name information.

The NIS+ domain name option code is 30. For more information on DHCP options and suboptions, see the "DHCPv6 Options" appendix in the Network Registrar User's Guide, Release 6.2.

Examples

The following example shows how to enable the IPv6 server to specify the NIS+ domain name of a client:

nisp domain-name cisco1.com

Related Commands

ntp access-group

To control access to the Network Time Protocol (NTP) services on the system, use the ntp access-group command in global configuration mode. To remove access control to the NTP services, use the no form of this command.

ntp access-group {peer | query-only | serve | serve-only} {access-list-number | access-list-number-expanded | access-list-name} [kod]

no ntp [access-group {peer | query-only | serve | serve-only} {access-list-number | access-list-number-expanded | access-list-name}]

Syntax Description

peer	Allows time requests and NTP control queries and allows the system to synchronize to the remote system.
query-only	Allows only NTP control queries. See RFC 1305 (NTP version 3).
serve	Allows time requests and NTP control queries, but does not allow the system to synchronize to the remote system.
serve-only	Allows only time requests. Note You must configure the ntp server ip-address command before using the serve-only keyword.
access-list-number	Number (from 1 to 99) of a standard IPv4 access list.
access-list-number-expanded	Number (from 1300 to 1999) of an expanded range IPv4 access list.
access-list-name	Name of an access list.
kod	(Optional) Sends the "Kiss-o-Death" (KOD) packet to any host that tries to send a packet that is not compliant with the access-group policy.

Command Default

By default, there is no access control. Full access is granted to all systems.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

The access group options are scanned in the following order from the least restrictive to most restrictive:

1. peer

2. query-only

3. serve

4. serve-only

Access is granted for the first match that is found. If no access groups are specified, all access is granted to all sources. If you specify any access groups, only the specified access is granted. This facility provides minimal security for the time services of the system. However, it can be circumvented by a determined programmer. If tighter security is desired, use the NTP authentication facility.

The NTP service can be activated by entering any ntp command. When you use the ntp access-group command, the NTP service is activated (if it has not already been activated) and access control to NTP services is configured simultaneously.

When you enter the no ntp access-group command, only access control to NTP services is removed. The NTP service itself remains active, along with any other previously configured NTP functions.

To disable the NTP service on a device, use the no ntp command without any keywords in global configuration mode. For example, if you want to remove not only the access control to NTP services, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Examples

The following example shows how to configure a system to allow itself to be synchronized by a peer from access list 99. However, the system restricts access to allow only time requests from access list 42.

Router(config)# ntp access-group peer 99

Router(config)# ntp access-group serve-only 42

In the following IPv6 example, a KOD packet is sent to any host that tries to send a packet that is not compliant with the access-group policy:

Router(config)# ntp access-group serve acl1 kod 

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

Related Commands

ntp authenticate

To enable Network Time Protocol (NTP) authentication, use the ntp authenticate command in global configuration mode. To disable the function, use the no form of this command.

ntp authenticate

no ntp [authenticate]

Syntax Description

This command has no arguments or keywords.

Command Default

By default, NTP authentication is not enabled.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Use this command if you want to authenticate NTP. If this command is specified, the system will not synchronize to another system unless it carries one of the authentication keys specified in the ntp trusted-key global configuration command.

The NTP service can be activated by entering any ntp command. When you use the ntp authenticate command, the NTP service is activated (if it has not already been activated) and NTP authentication is enabled simultaneously.

In the no form of any ntp command, all the keywords are optional. When you enter the no ntp authenticate command, only the NTP authentication is removed from the NTP service. The NTP service itself remains active, along with any other functions you that previously configured.

To disable the NTP service on a device, you must enter the no ntp command without any keywords in global configuration mode. For example, if you previously issued the ntp authenticate command and you now want to disable not only the authentication, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Examples

The following example shows how to configure the system to synchronize only to systems that provide the authentication key 42 in their NTP packets:

Router(config)# ntp authenticate

Router(config)# ntp authentication-key 42 md5 aNiceKey

Router(config)# ntp trusted-key 42

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

Related Commands

ntp authentication-key

To define an authentication key for Network Time Protocol (NTP), use the ntp authentication-key command in global configuration mode. To remove the authentication key for NTP, use the no form of this command.

ntp authentication-key number md5 key [encryption-type]

no ntp [authentication-key number]

Syntax Description

Command Default

No authentication key is defined for NTP.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Use this command to define authentication keys for use with other NTP commands in order to provide a higher degree of security.

Note When this command is written to NVRAM, the key is encrypted so that it is not displayed in the configuration.

When you configure the authentication key using the ntp authentication-key command or using the auto secure ntp command, if the length of the MD5 key exceeds 32 characters, an error message is displayed.

The NTP service can be activated by entering any ntp command. When you use the ntp authentication-key command, the NTP service is activated (if it has not already been activated) and the NTP authentication key is defined simultaneously.

When you enter the no ntp authentication-key command, only the NTP authentication key is removed from the NTP service. The NTP service itself remains active, along with any other previously configured NTP functions.

Note If a specific authentication key configuration is removed, the NTP process is not stopped until all the authentication key configurations are removed.

To disable the NTP service on a device, use the no ntp command without any keywords in global configuration mode. For example, if you want to remove not only the access control to NTP services, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Examples

The following example shows how to configure the system to synchronize only to systems providing the authentication key 42 in their NTP packets:

Router(config)# ntp authenticate

Router(config)# ntp authentication-key 42 md5 aNiceKey

Router(config)# ntp trusted-key 42

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

The following example shows the error message displayed when the authentication key character string length exceeds 32:

Router(config)# ntp authentication-key 23 md5 11111111111111111111111111111111111

%NTP: Key too long

Related Commands

ntp broadcast client

To configure a device to receive Network Time Protocol (NTP) broadcast messages on a specified interface, use the ntp broadcast client command in interface configuration mode. To disable this capability, use the no form of this command.

ntp broadcast client [novolley]

no ntp [broadcast [client]]

Syntax Description

Command Default

By default, an interface is not configured to receive NTP broadcast messages.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

Use this command to allow the system to listen to broadcast packets on an interface-by-interface basis.

The NTP service can be activated by entering any ntp command. When you use the ntp broadcast client command, the NTP service is activated (if it has not already been activated) and the device is configured to receive NTP broadcast packets on a specified interface simultaneously.

In the no form of any ntp command, all the keywords are optional. When you enter the no ntp broadcast client command, only the broadcast client configuration is removed from the NTP service. The NTP service itself remains active, along with any other functions that you previously configured.

To disable the NTP service on a device, you must enter the no ntp command without any keywords. For example, if you previously issued the ntp broadcast client command and you now want to remove not only the broadcast client capability, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

In IPv6 configuration, the ntp broadcastdelay command is used when the ntp broadcast client or ntp multicast client command is configured with the novolley keyword.

Examples

In the following example, the system is configured to receive (listen to) NTP broadcasts on Ethernet interface 1:

Router(config)# interface ethernet 1

Router(config-if)# ntp broadcast client

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

Related Commands

ntp broadcastdelay

To set the estimated round-trip delay between the Cisco IOS software and a Network Time Protocol (NTP) broadcast server, use the ntp broadcastdelay command in global configuration mode. To revert to the default value, use the no form of this command.

ntp broadcastdelay microseconds

no ntp [broadcastdelay]

Syntax Description

Command Default

By default, the round-trip delay between the Cisco IOS software and an NTP broadcast server is 3000 microseconds.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Use the ntp broadcastdelay command when the router is configured as a broadcast client and the round-trip delay on the network is other than 3000 microseconds. In IPv6, the value set by this command should be used only when the ntp broadcast client and ntp multicast client commands have the novolley keyword enabled.

The NTP service can be activated by entering any ntp command. When you use the ntp broadcastdelay command, the NTP service is activated (if it has not already been activated) and the estimated round-trip delay between the Cisco IOS software and an NTP broadcast server is set simultaneously.

In the no form of any ntp command, all the keywords are optional. When you enter the no ntp broadcastdelay command, only the estimated round-trip delay between the Cisco IOS software and an NTP broadcast server is removed from the NTP service. The NTP service itself remains active, along with any other functions you previously configured.

To disable the NTP service on a device, you must enter the no ntp command without any keywords in global configuration mode. For example, if you previously issued the ntp broadcastdelay command and you now want to remove not only the delay setting, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Examples

The following example shows how to set the estimated round-trip delay between a router and the broadcast client to 5000 microseconds:

Router(config)# ntp broadcastdelay 5000

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

Related Commands

ntp disable

To prevent an interface from receiving Network Time Protocol (NTP) packets, use the ntp disable command in interface configuration mode. To enable the receipt of NTP packets on an interface, use the no form of this command.

ntp disable [ip | ipv6]

no ntp disable [ip | ipv6]

Syntax Description

Command Default

By default, interfaces receive NTP packets.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

This command provides a simple method of access control.

Use the ntp disable command in interface configuration mode to configure an interface to reject NTP packets. If the ntp disable command is configured on an interface that does not have any NTP service running, the interface remains disabled even after the NTP service is started by another NTP configuration. When you use the ntp disable command without the ip or ipv6 keyword, NTP is disabled on the interface for all the address families.

When you enter the no ntp disable command in interface configuration mode, the interface that was configured to reject NTP packets is enabled to receive NTP packets.

Note Remove all NTP commands from an interface before entering the ntp disable command on that interface.

Configuring the ntp disable command on an interface does not stop the NTP service. To disable the NTP service on a device, use the no ntp command without keywords in global configuration mode. For example, if you had previously issued the ntp disable command and you now want to remove not only this restriction, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Examples

The following example shows how to prevent Ethernet interface 0 from receiving NTP packets:

Router(config)# interface ethernet 0

Router(config-if)# ntp disable

The following example shows the message displayed when you try to execute the ntp disable command on an interface that has other NTP commands configured on it:

Router(config-if)# ntp disable

%NTP: Unconfigure other NTP commands on this interface before executing 'ntp disable'

If you had previously issued the ntp disable command and you now want to remove not only this restriction, but also all NTP functions from the device, use the no ntp command without keywords in global configuration mode. The following example shows how to disable the NTP service on a device:

Router(config)# no ntp

Related Commands

ntp clear drift

To reset the drift value stored in the persistent data file, use the ntp clear drift command in privileged EXEC mode.

ntp clear drift

Syntax Description

This command has no arguments or keywords.

Command Default

The drift value stored in the persistent data file is not reset.

Command Modes

Privileged EXEC (#)

Command History

Usage Guidelines

The ntp clear drift command is used to reset the local clock drift value in the persistent data file. The drift is the frequency offset between the local clock hardware and the authoritative time from the Network Time Protocol version 4 (NTPv4) servers. NTPv4 automatically computes this drift and uses it to compensate permanently for local clock imperfections.

This command is available only when the NTP service is activated using any ntp command in global configuration mode.

Examples

The following example shows how to reset the drift value in the persistent data file:

Router# ntp clear drift

Related Commands

ntp logging

To enable Network Time Protocol (NTP) message logging, use the ntp logging command in global configuration mode. To disable NTP logging, use the no form of this command.

ntp logging

no ntp [logging]

Syntax Description

This command has no arguments or keywords.

Command Default

NTP message logging is disabled.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Use the ntp logging command to control the display of NTP logging messages.

The NTP service can be activated by entering any ntp command. When you use the ntp logging command, the NTP service is activated (if it has not already been activated) and message logging is enabled simultaneously.

In the no form of any ntp command, all the keywords are optional. When you enter the no ntp logging command, only message logging is disabled in the NTP service. The NTP service itself remains active, along with any other functions that you previously configured.

To disable the NTP service on a device, you must enter the no ntp command without keywords. For example, if you previously issued the ntp logging command and you now want to disable not only the message logging, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Examples

The following example shows how to enable NTP message logging and verify that it is enabled:

Router# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# ntp logging

Router(config)# end

Router# show running-config | include ntp

ntp logging

ntp clock-period 17180152

ntp peer 10.0.0.1

ntp server 192.168.166.3

The following example shows how to disable NTP message logging and verify to that it is disabled:

Router# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# no ntp logging

Router# end

Router(config)# show running-config | include ntp

ntp clock-period 17180152

ntp peer 10.0.0.1

ntp server 192.168.166.3

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

Related Commands

ntp master

To configure the Cisco IOS software as a Network Time Protocol (NTP) master clock to which peers synchronize themselves when an external NTP source is not available, use the ntp master command in global configuration mode. To disable the master clock function, use the no form of this command.

ntp master [stratum]

no ntp [master]

Caution Use this command with caution. Valid time sources can be easily overridden using this command, especially if a low stratum number is configured. Configuring multiple devices in the same network with the ntp master command can cause instability in keeping time if the devices do not agree on the time.

Syntax Description

Command Default

By default, the master clock function is disabled. When enabled, the default stratum is 8.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Because the Cisco implementation of NTP does not support directly attached radio or atomic clocks, the router is normally synchronized, directly or indirectly, to an external system that has such a clock. In a network without Internet connectivity, such a time source may not be available. The ntp master command is used in such cases.

A system with the ntp master command configured that cannot reach any clock with a lower stratum number will claim to be synchronized at the configured stratum number, and other systems will be willing to synchronize to it via NTP.

Note The software clock must have been set from some source, including manual setting, before the ntp master command will have any effect. This protects against distributing erroneous time after the system is restarted.

The NTP service can be activated by entering any ntp command. When you use the ntp master command, the NTP service is activated (if it has not already been activated) and the Cisco IOS software is configured as an NTP master clock simultaneously. When you enter the no ntp master command, only the NTP master clock configuration is removed from the NTP service. The NTP service itself remains active, along with any other functions that you previously configured.

To disable the NTP service on a device, you must enter the no ntp command without any keywords in global configuration mode. For example, if you had previously issued the ntp master command and you now want to remove not only the master clock function, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Examples

The following example shows how to configure a router as an NTP master clock to which peers may synchronize:

Router(config)# ntp master 10

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

Related Commands

ntp max-associations

To configure the maximum number of Network Time Protocol (NTP) peers and clients for a routing device, use the ntp max-associations command in global configuration mode. To return the maximum associations value to the default, use the no form of this command.

ntp max-associations number

no ntp [max-associations]

Syntax Description

Command Default

The maximum association value of NTP peers and clients is 100.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

The router can be configured to define the maximum number of NTP peer and client associations that the router will serve. Use the ntp max-associations command to set the maximum number of NTP peer and client associations that the router will serve.

The ntp max-associations command is useful for ensuring that the router is not overwhelmed by NTP synchronization requests. For an NTP master server, this command is useful for allowing numerous devices to synchronize to a router.

The NTP service can be activated by entering any ntp command. When you use the ntp max-associations command, the NTP service is activated (if it has not already been activated) and the maximum number of NTP peers and clients is configured simultaneously.

In the no form of any ntp command, all the keywords are optional. When you enter the no ntp max-associations command, only the maximum number value is removed from the NTP service. The NTP service itself remains active, along with any other functions that you previously configured.

To disable the NTP service on a device, you must enter the no ntp command without any keywords in global configuration mode. For example, if you previously issued the ntp max-associations command and you now want to remove not only that maximum value, but also all NTP functions from the device, use the no ntp command without any keywords. This ensures that all NTP functions are removed and that the NTP service is also disabled.

Note By default, the previous configuration values are retained when the last valid configuration (configuration for which the NTP service needs to run) is removed. Only the configuration values related to the maximum number of NTP peer and client associations are reset to the default value when the NTP process is disabled.

Examples

In the following example, the router is configured to act as an NTP server to 200 clients:

Router(config)# ntp max-associations 200 

The following example shows how to remove all the configured NTP options and disable the NTP server:

Router(config)# no ntp

Related Commands

ntp multicast

To configure a system to send Network Time Protocol (NTP) multicast packets on a specified interface, use the ntp multicast command in interface configuration mode. To disable this capability, use the no form of this command.

ntp multicast [ip-address | ipv6-address] [key key-id] [ttl value] [version number]

no ntp [multicast [ip-address | ipv6-address] [key key-id] [ttl value] [version number]]

Syntax Description

Command Default

NTP multicast capability is disabled.

Command Modes

Interface configuration (config-if)

Command History