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Syntax Description:

• ip-address— Neighbor’s IP address.

• peer-group-name— Name of the peer group. See section 8-19.

Purpose: To remove private autonomous systems in updates to the neighbor or peer group. Private AS numbers are in the range 64512 to 65535. Private AS numbers should not be advertised to the Internet. The following conditions apply when using this command:

• Use only with EBGP peers.

• If the update has only private AS numbers in the AS path, BGP removes them.

• If the AS path includes both private and public AS numbers, BGP doesn’t remove the private AS numbers. This situation is considered a configuration error.

• If the AS path contains the AS number of the EBGP neighbor, BGP doesn’t remove the private AS number.

• If the AS path contains confederations, BGP removes the private AS numbers only if they come after the confederation portion of the AS path.

Cisco IOS Software Release: 12.0

Configuration Example: Removing a Private AS Number from Updates to Neighbors or Peer Groups

In Figure 8-24, an ISP is connected to a customer who is using a private AS number. The ISP is connected to another ISP for Internet connectivity. The ISP in AS 1 needs to remove the private AS number before advertising routes to the ISP in AS 2.

Figure 8-24. Private AS Numbers Should Be Suppressed If Routes Are Advertised to the Internet

Router A

router bgp 65530

 network 172.16.0.0 mask 255.255.255.0

 network 172.16.1.0 mask 255.255.255.0

 network 172.16.2.0 mask 255.255.255.0

 network 172.16.3.0 mask 255.255.255.0

 neighbor 10.1.1.2 remote-as 1

__________________________________________________________________________

Router B

router bgp 1

 neighbor 10.1.1.1 remote-as 65530

 neighbor 10.1.2.2 remote-as 2

 neighbor 10.1.2.2 remove-private-as

__________________________________________________________________________

Router C

router bgp 2

 neighbor 10.1.2.1 remote-as 1

Verification

Before using the command neighbor 10.1.2.2 remove-private-as, check the BGP tables on Routers B and C to view the private AS number in the AS path:

rtrB#show ip bgp

BGP table version is 21, local router ID is 172.16.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 172.16.0.0/24    10.1.1.1                 0             0 65530 i

*> 172.16.1.0/24    10.1.1.1                 0             0 65530 i

*> 172.16.2.0/24    10.1.1.1                 0             0 65530 i

*> 172.16.3.0/24    10.1.1.1                 0             0 65530 i

__________________________________________________________________________

rtrC#show ip bgp

BGP table version is 5, local router ID is 156.26.32.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 172.16.0.0/24    10.1.2.1                               0 1 65530 i

*> 172.16.1.0/24    10.1.2.1                               0 1 65530 i

*> 172.16.2.0/24    10.1.2.1                               0 1 65530 i

*> 172.16.3.0/24    10.1.2.1                               0 1 65530 i

Now add the command neighbor 10.1.2.2 remove-private-as on Router B and recheck the BGP table on Router C:

rtrC#show ip bgp

BGP table version is 5, local router ID is 156.26.32.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 172.16.0.0/24    10.1.2.1                               0 1 i

*> 172.16.1.0/24    10.1.2.1                               0 1 i

*> 172.16.2.0/24    10.1.2.1                               0 1 i

*> 172.16.3.0/24    10.1.2.1                               0 1 i

As you can see, the private AS number (65530) has been removed.

Troubleshooting

1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

   If the neighbor relationship is not in the Established state, see section 8-23.

2. Verify that the private AS numbers have been removed by using show ip bgp.

3. If the private AS numbers have not been removed, check the neighbor’s IP address or peer group name in the remove-private-as command.

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