More detail on how Cisco does this at: http://www.cisco.com/warp/public/459/25.shtml specifically, see step 10: "10. When both paths are external, prefer the path that was received first (the oldest one). This step minimizes route-flap, since a newer path won't displace an older one, even if it was the preferred route based on additional decision criteria, as described in steps 11, 12, and 13. Skip this step if any of the following is true: * The bgp best path compare-routerid command is enabled. Note: This command was introduced in Cisco IOS® Software Releases 12.0.11S, 12.0.11SC, 12.0.11S3, 12.1.3, 12.1.3AA, 12.1.3.T, and 12.1.3.E. ' * The router ID is the same for multiple paths, since the routes were received from the same router. * There is no current best path. An example of losing the current best path occurs when the neighbor offering the path goes down." -Nick On Wed, Jun 26, 2002 at 06:12:18PM -0400, Mathew Richardson wrote:
In the interest of accuracy, it's worth noting that some vendors will choose the one with the lower router ID, and others will choose the route that was learned first (at least by default), despite documentation to the contrary.
mrr