Hi All,
I was working on one of the labs and I came across some problems which it has been fixed, but I thought I will Spam the OSL with it maybe it can help someone. The part of the lab where I was struggling is the the BGP peering: Two routers R2 and R4 both in the same Main AS #1 and they are peering with Local-as command to make them peer as E-BGP neighbors. The tricky part is when the peering was established, both routers where not able to exchange routing-updates so no prefixes are exchange. It seems to me still as the peer with different AS # they see each other as I-BGP so the rule of IBGP is applied which is Ibgp learned route is not advertised to ibgp neighbor. During my study I have understood that when the router peer with its neighbor it compare its own AS # with the neighbor AS# to decide whether its IBGP or E-BGP neighbor. This seems not the case! Anyhow after searching Cisco site I found that the Local-as command will pre-pand additional AS# in the AS_SEQUENCE carried with the Path-List attribute! in the form of (local-as, Real-as) "*104, 1*" This can explain why they didn't learn each other prefixes because its carried along the path-list basic bgp routing-loops prevention is ignores the updates. To work around this mess I used the following command: *neighbor x.x.x.x* *local-as 102* *no-prepend replace-as* Attached is the topology used for this lab. I hop this can be informative. Regards, Abdel
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