peer allow-as-loop
Function
The peer allow-as-loop command sets the number of local AS number repetitions.
The undo peer allow-as-loop command restores the default setting.
By default, the local AS number cannot be repeated.
Format
peer { group-name | ipv4-address | ipv6-address } allow-as-loop [ number ] [ global-as [ vpn-as ] ]
undo peer { group-name | ipv4-address | ipv6-address } allow-as-loop [ number ] [ global-as [ vpn-as ] ]
Parameters
| Parameter | Description | Value |
|---|---|---|
group-name |
Specifies the name of a peer group. |
The name is a string of 1 to 47 case-sensitive characters, with spaces not supported. When double quotation marks are used around the string, spaces are allowed in the string. |
ipv4-address |
Specifies the IPv4 address of a peer. |
It is in dotted decimal notation. |
ipv6-address |
Specifies the IPv6 address of a peer. |
The value is a 32-digit hexadecimal number, in the format of X:X:X:X:X:X:X:X. |
number |
Specifies the number of local AS number repetitions. |
The value is an integer that ranges from 1 to 10. The default value is 1. |
global-as |
Specifies a global AS number. |
- |
vpn-as |
Specifies a VPN instance AS number. |
- |
ipv4-address is valid only in the BGP view, BGP-IPv4 unicast address family view, BGP-IPv4 multicast address family view, BGP-VPN instance IPv4 address family view, BGP-VPNv4 address family view, BGP-IPv6 unicast address family view, BGP-VPNv6 address family view, BGP-VPLS address family view, BGP-L2VPN address family view, and BGP L2VPN-AD address family view.
ipv6-address is valid only in the BGP-IPv6 unicast address family view and BGP-VPN instance IPv6 address family view.
- The global-as and vpn-as parameters apply only to BGP VPN instance IPv4 and BGP VPN instance IPv6 address family views.
Views
BGP view, BGP-IPv4 unicast address family view, BGP-IPv4 multicast address family view, BGP-VPN instance IPv4 address family view, BGP-VPNv4 address family view, BGP-IPv6 unicast address family view, BGP-VPN instance IPv6 address family view, BGP-VPNv6 address family view, BGP-VPLS address family view, BGP-L2VPN address family view, BGP L2VPN-AD address family view
Usage Guidelines
Usage Scenario
BGP uses AS numbers to detect routing loops. The AS numbers in the AS_Path of each received route are matched against the local AS number configured using the bgp command, the fake AS number configured using the peer fake-as command, and the VPN instance AS number configured using the as-number command. The largest number of times any of the configured AS numbers is repeated is considered as the maximum number. In the Hub and Spoke networking, if EBGP runs between a Hub-PE and a Hub-CE on a Hub site, the route sent from the Hub-PE to the Hub-CE carries the AS number of the Hub-PE. If the Hub-CE sends a routing update to the Hub-PE, the Hub-PE will deny it because the routing update contains the AS number of the Hub-PE.
To ensure proper route transmission in the Hub and Spoke networking, configure all the BGP peers on the path, along which the Hub-CE advertises private network routes to the Spoke-CE, to accept the routes in which the AS number repeats once.
Prerequisites
Peer relationships have been established using the peer as-number command.
Precautions
If the peer allow-as-loop command is run for a peer or peer group multiple times, the latest configuration overrides the previous one.