Removing Private AS Numbers from Updates

You might choose to conserve AS numbers by assigning private AS numbers to some customers. You can assign private AS numbers from the range 64,512 to 65,535. However, when BGP advertises prefixes to other ISPs, it is undesirable to include the private AS numbers in the path. Configure the external neighbors to drop the numbers with the neighbor remove-private-as command.

neighbor remove-private-as

• Use to remove private AS numbers only in updates sent to external peers.
• All private AS numbers are removed regardless of their position in the AS-path attribute and regardless of the presence of public AS numbers.
• If you specify a BGP peer group by using the peerGroupName argument, all the members of the peer group inherit the characteristic configured with this command. You cannot override the characteristic for a specific member of the peer group.
• Example

  host1(config-router)#neighbor 10.10.128.52 remove-private-as

• New policy values are applied to all routes that are sent (outbound policy) or received (inbound policy) after you issue the command.

  To apply the new policy to routes that are already present in the BGP routing table, you must use the clear ip bgp command to perform a soft clear or hard clear of the current BGP session.

  Behavior is different for outbound policies configured for peer groups for which you have enabled Adj-RIBs-Out. If you change the outbound policy for such a peer group and want to fill the Adj-RIBs-Out table for that peer group with the results of the new policy, you must use the clear ip bgp peer-group command to perform a hard clear or outbound soft clear of the peer group. You cannot merely perform a hard clear or outbound soft clear for individual peer group members because that causes BGP to resend only the contents of the Adj-RIBs-Out table.

• Use the no version to halt the removal of private AS numbers in updates sent to external peers. Use the default version to remove the explicit configuration from the peer or peer group and reestablish inheritance of the feature configuration.
• See neighbor remove-private-as

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