neighbor as-override

Replaces the autonomous system number (ASN) of the originating device with the ASN of the sending BGP device.

Syntax

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

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

Command Default

This feature is disabled.

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.

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 feature.

BGP loop prevention verifies the ASN in the AS path. If the receiving router sees its own ASN in the AS path of the received BGP packet, the packet is dropped. The receiving router assumes that the packet originated from its own AS and has reached the place of origination. This can be a significant problem if the same ASN is used among various sites, preventing sites with identical ASNs from being linked by another ASN. In this case, routing updates are dropped when another site receives them.

Examples

This example replaces the ASN globally.

device# configure terminal
device(config)# router bgp
device(config-bgp-router)# neighbor 10.11.12.13 as-override

This example replaces the BGP4+ ASN for VRF instance "red".

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