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Re: bgp peering+RR posted 10/13/2007
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Here's my assumption flow:
R1 is learning the route via eBGP initially
R1 passing to R3 via iBGP.
R3 is reflecting it to R2 and R5 as they are both client of R3.
R3 is not advertising it to R4 (as R4 is a non-client and R1 is a
non-client).
R2 and R5 has no mechanism to advertise back to R4 as R2 and R5 aren't route
reflectors and they are learning the route via iBGP from R3.



On 10/13/07, Joseph Saad <joseph.samir.saad@xxxxxxxxx> wrote:
>
>           R1
>          /   \
>        /      \
>       r3-----r4
>      /  \      / \
>    /     \    /   \
> r2      r5       r2
>
> I still disagree, R4 couldn't be possibly learning the route from R2.
>
> The statement of "if R2 is learning it, it will pass to the entire domain
> including R1" is flawed because R2 is not a ROUTE-REFLECTOR. It's merely a
> CLIENT to both R3 and R4 as per the original post  .... "I am planning to
> make r2 and r5 as rr-clients for r3 and r4" ...
>
> so iBGP learnt route on R2 reflected from R3 can't be possibly be
> reflected to other neighbors as this breaks the full mesh rule and R2 is not
> a route-reflector.
>
> Let's review the assumptions: R3, R4 are Route reflectors. Both of R2 and
> R5 are each a route-reflector of client of both R3 and R4.
>
> We may need a 3rd opinion on the topic.
>
> I am afraid that one of us is missing something, but I don't know who.
>
> Cheers,
> Joseph.
>
> On 10/12/07, shiran guez < shiranp3@xxxxxxxxx> wrote:
> >
> > Please notice to the initial note both R3 and R4 are RR Server for R2
> > and R5!
> > and for that meter both R3 and R4 learned the same from R1 and they
> > reflect to R2 and R5.
> > also if R2 is learning it will pass to the entire domain including R1.
> >
> >
> >
> > On 10/11/07, Joseph Saad <joseph.samir.saad@xxxxxxxxx > wrote:
> > >
> > > whether R1 and R4 Loopbacks still reachable by R4 and R1 respectively.
> > > Independent of Route reflection, if reachability is maintained via
> > > other
> > > means (e.g. via R3) the R1 eBGP-learnt routes will be advertised to R4
> > > via
> > > the direct iBGP peering between R1 and R4. in Summary, the iBGP
> > > peering is
> > > not broken in the first place.
> > >
> > > If not, then you need to consider the Route-reflection rules.
> > >
> > > Jeff Dolye Page 137: RFC 1966 defines three rules that the RR uses to
> > > determine who the route is advertised to, depending on how the route
> > > was
> > > learned:
> > > l If the route was learned from a non-client IBGP peer, it is
> > > reflected to
> > > clients only.
> > > l If the route was learned from a client, it is reflected to all
> > > nonclients
> > > and clients, except for the originating client.
> > > l If the route was learned from an EBGP peer, it is reflected to all
> > > clients
> > > and nonclients.
> > >
> > > with R3 as the route-reflector, it has learnt the route via a
> > > non-client
> > > iBGP peer (from R1), hence it will be reflected to clients only (R2 &
> > > R5).
> > > Which means R4 shouldn't receive it.
> > >
> > > Hope this helps.
> > >
> > > Joseph.
> > >
> > > On 10/10/07, slevin kremera < slevin.kremera@xxxxxxxxx > wrote:
> > > >
> > > >           R1
> > > >          /   \
> > > >        /      \
> > > >       r3-----r4
> > > >      /  \      / \
> > > >    /     \    /   \
> > > > r2      r5       r2
> > > >
> > > >
> > > > here all the routers are in as100.  r1-r3-r4 are full meshed and
> > > peering
> > > > wit
> > > > lo0. r2 and r5 are peering with r3 and r4..I am planning to make r2
> > > and r5
> > > >
> > > > as rr-clients for r3 and r4
> > > >
> > > > .The question here is if the link between r1 and r4 is broken and r1
> > > > recieves an ebgp updates from outside..will it fwd it to R4??
> > > >
> > > >
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> >
> >
> > --
> > Shiran Guez
> > MCSE CCNP NCE1
> > http://cciep3.blogspot.com
> > http://www.linkedin.com/in/cciep3