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BGP Fundamentals

Chapter Description

In This sample chapter from Troubleshooting BGP: A Practical Guide to Understanding and Troubleshooting BGP, the authors cover BGP Messages and Inter-Router Communication, Basic BGP Configuration for IOS, IOS XR, and NX-OS, IBGP Rules, EBGP Rules, and BGP Route Aggregation

Remove Private AS

Some organizations might not be able to meet the qualifications for obtaining their own ASN but still want to receive Internet routing tables from their service provider. In these situations, the service provider may assign the organization a private ASN for peering. Private ASNs should not be advertised by the service provider to other ISPs on the Internet.

The feature remove private AS removes the private AS of routes that are advertised to the configured peer. The router performs the following path analysis with the remove private AS feature:

  • Removes only private ASNs on routes advertised to EBGP peers.

  • If the AS-Path for the route has only private ASNs, the private ASNs are removed.

  • If the AS-Path for the route has a private ASN between public ASNs, it is assumed that this is a design choice, and the private ASN is not removed

  • If the AS-Path contains confederations (AS_CONFED_SEQ), BGP removes the private AS numbers only if they are included after the AS_CONFED_SEQ (Confederation AS-Path) of the path.

The remove private AS feature is configured on IOS nodes with the BGP address-family configuration command neighbor ip-address remove-private-as. IOS XR and NX-OS devices use the BGP neighbor address-family configuration command remove-private-as.

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