Hi All,
I don't see an attachment. Is that something that is filtered?
Thanks,
Regards,
Lukasz
On Fri, 15 Jul 2011 11:40:34 +0200, Abdel el Anazi wrote:
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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