Your right Christophe, thank you for mentioning the allow-as in I total
forget that option.

Great this is the power of group study!



2011/7/15 Christophe Lemaire <[email protected]>

> Hi Abdel,
>
> > 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 is the case. R1 and R2 still see each other as eBGP neighbor. But
> as you pointed out, when you use the local-as command, the router
> prepends its real AS # by default. And as R1 and R2's real AS # are
> the same, the BGP loop prevention enter in action: Routers refuse all
> NLRI containing  their own AS # in the AS_PATH. (You can see it with
> "debup ip bgp updates").
>
> Your workaround simply prevent the routers to prepend their real AS#
> and to replace it by the fake AS# (or local-as).
>
> Another option could be to use "neighbor x.x.x.x allowas-in" command.
> This disable the AS_PATH check for updates coming from that neighbor.
>
> Regards,
> Christophe
>
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