Reg:IBGP routes issue

vinod kumar · May 2009

Hi All,

I have litlle confusion about ibgp functionality.As we know in EBGP we use AS path information to prevent loops.But if we receive a route from a IBGP peer then why we do not advertise the same route to that ibgp peer.As we know in case of RR we use cluster-id to prevent loops but what we use in ibgp.Bgp split-horizon rule says that routes learned via a n ibgp peer will not advertise to another ibgp peer as it assumes that ibgp is fully meshed but why we cann't advertise the route to the same ibgp peer from which we learned the router.

Please help me.

Thanks

Scott Morris · May 2009

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Be careful with your wording or you will irritate Anthony.

There
is not "split horizon" in BGP, but the rules makes it LIKE split
horizon. hehehehe.

But I think you answer your own question there. And you do find
instances where the same route IS passed both directions, but if I
learn a route from you, the only reason I'll pass the same route back
to you is if I have something better. If the route FROM you is my
bestpath, why would I tell you about it, because you're already telling
me!

HTH,

Scott Morris, CCIEx4
(R&S/ISP-Dial/Security/Service Provider) #4713,

JNCIE-M #153, JNCIS-ER, CISSP, et al.

CCSI #21903, JNCI-M, JNCI-ER

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vinod kumar wrote:

Hi All,

I have litlle confusion about ibgp functionality.As we know in
EBGP we use AS path information to prevent loops.But if we receive a
route from a IBGP peer then why we do not advertise the same route to
that ibgp peer.As we know in case of RR we use cluster-id to prevent
loops but what we use in ibgp.Bgp split-horizon rule says that routes
learned via a n ibgp peer will not advertise to another ibgp peer as it
assumes that ibgp is fully meshed but why we cann't advertise the route
to the same ibgp peer from which we learned the router.

Please help me.

Thanks

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Reg:IBGP routes issue

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