neighbor enforce-first-as

Ensures that a device requires the first ASN listed in the AS_SEQUENCE field of an AS path-update message from EBGP neighbors to be the ASN of the neighbor that sent the update.

Syntax

neighbor { ip-address | ipv6-address | peer-group-name } enforce-first-as [ disable | enable ]

no neighbor { ip-address | ipv6-address | peer-group-name } enforce-first-as [ disable | enable ]

Command Default

Disabled by default.

Parameters

ip-address: IPv4 address of the neighbor.
ipv6-address: IPv6 address of the neighbor.
peer-group-name: Peer group name configured by the neighbor peer-group-name command.
disable: Disables this feature.
enable: Enables this feature.

Modes

BGP configuration mode

BGP address-family IPv4 unicast VRF configuration mode

BGP address-family IPv6 unicast VRF configuration mode

Usage Guidelines

Use the no form of this command to disable this requirement globally for the device.

Examples

This example enables the enforce-first-as feature for a specified neighbor.

device# configure terminal
device(config)# router bgp
device(config-bgp-router)# neighbor 10.11.12.13 enforce-first-as enable

This example enables the enforce-first-as feature for a BGP4+ specified neighbor for VRF instance "red".

device# configure terminal
device(config)# router bgp
device(config-bgp-router)# address-family ipv6 unicast
device(config-bgp-ipv6u-vrf)# neighbor 2001:2018:8192::125 enforce-first-as enable