On Thu, Mar 18, 2010 at 17:17, Taqdir Singh <[email protected]> wrote: > Hi Patrice, > > thats my question, why by default eBGP next hop is always carried in local > AS , why BGP is designed so ?
It was designed in such a way because the assumption behind BGP is that routing WITHIN AS is already working properly and that all networks are reachable. The reasons for next-hop being carried as it is are that if the external network is not reachable, neither will be the route. The decision to drop the traffic will be made by the node that has next-hop as unreachable, without hauling the traffic throughout your AS only to have it dropped at egress node - which is the behavior you get with "next-hop-self". Since BGP is all about efficiency, this is preferred default behavior. If you wish to change it, you may feel free to do so. In MPLS designs, additional reason to carry unchanged next-hop is to preserve the next-hop label advertised by neighboring AS in a case of Inter-AS MPLS VPNs. -- Marko Milivojevic - CCIE #18427 Senior Technical Instructor - IPexpert YES! We include 400 hours of REAL rack time with our Blended Learning Solution! Mailto: [email protected] Telephone: +1.810.326.1444 Fax: +1.810.454.0130 Web: http://www.ipexpert.com/ _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
