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Allowing an AS Number to Appear in its Own AS Path
This command allows you to set the number of times a particular AS number can occur in the AS path.
The allow-as feature permits a BGP speaker to allow the ASN to be present for a specified number of
times in the update received from the peer, even if that ASN matches its own. The AS-PATH loop is
detected if the local ASN is present more than the specified number of times in the command.
• Allow this neighbor ID to use the AS path the specified number of times.
CONFIG-ROUTER-BGP mode
neighbor {IP address | peer-group-name} allowas-in number
– Peer Group Name: 16 characters.
– Number: 1 through 10.
Format: IP Address: A.B.C.D.
You must Configure Peer Groups before assigning it to an AS.
Example of Viewing AS Numbers in AS Paths
The lines shown in bold are the number of times ASN 65123 can appear in the AS path (allows–in 9).
To disable this feature, use the no neighbor allow-as in number command in CONFIGURATION
ROUTER BGP mode.
R2(conf-router_bgp)#show conf
!
router bgp 65123
bgp router-id 192.168.10.2
network 10.10.21.0/24
network 10.10.32.0/24
network 100.10.92.0/24
network 192.168.10.0/24
bgp four-octet-as-support
neighbor 10.10.21.1 remote-as 65123
neighbor 10.10.21.1 filter-list Laura in
neighbor 10.10.21.1 no shutdown
neighbor 10.10.32.3 remote-as 65123
neighbor 10.10.32.3 no shutdown
neighbor 100.10.92.9 remote-as 65192
neighbor 100.10.92.9 local-as 6500
neighbor 100.10.92.9 no shutdown
neighbor 192.168.10.1 remote-as 65123
neighbor 192.168.10.1 update-source Loopback 0
neighbor 192.168.10.1 no shutdown
neighbor 192.168.12.2 remote-as 65123
neighbor 192.168.12.2 allowas-in 9
neighbor 192.168.12.2 update-source Loopback 0
neighbor 192.168.12.2 no shutdown
R2(conf-router_bgp)#R2(conf-router_bgp)#
Enabling Neighbor Graceful Restart
BGP graceful restart is active only when the neighbor becomes established. Otherwise, it is disabled.
Graceful-restart applies to all neighbors with established adjacency.
With the graceful restart feature, the system enables the receiving/restarting mode by default. In
Receiver-Only mode, graceful restart saves the advertised routes of peers that support this capability
180
Border Gateway Protocol IPv4 (BGPv4)