From: Gregory Gombas (ggombas@gmail.com)
Date: Thu Sep 27 2007 - 13:19:24 ART
Ben - I think Step 1 is correct but not step 2. As Cecil said ebgp has AD of 20.
Now since it prefers the locally originated route it ignores the BGP route.
Step 2 would be to look where that locally originated route came from,
in this case RIP, and then use the rip route.
So only the RIP route makes it to the routing table. I guess BGP is
smart enough to say that I'm not sending the locally originated BGP
route to the route table because it should already be in the route
table by some other source (protocol,connected,static, etc...)
Hopefully some CCIE's will put their 2 cents here...
On 9/27/07, Cecil Wilson <Cecil.Wilson@flextronics.com> wrote:
> Seems a little confusing
> 1. locally origin routes will be select oover ebgp however in terms
> of AD
> EBGP 20
> IBGP 200
> RIP 120
>
> So in terms of AD external BGP routes should be selected over IBGP?
>
> Im I looking at it wrong?
>
>
> Cecil G. Wilson
> IT Network Services
> Office: (901) 215-2710
> Cell: (901) 601-6201
> cecil.wilson@flextronics.com
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Ben
> Sent: Thursday, September 27, 2007 10:23 AM
> To: Gregory Gombas
> Cc: Cisco certification
> Subject: Re: RIP is preferred over eBGP!
>
> Gregory,
>
> Step 1: Router B is faced with two BGP sources, ebgp and locally
> originated (redistributed from RIP).
>
> BGP decision process will pick the locally originated over the ebgp
> route (Wendel Odom)
>
> W - weight
> L - local preference
> L - locally originated
> A - AS path
>
> O - Origin
> M - MED
> N - Neighbor Type
> I - cannot remember :)
>
>
> Step 2: BGP administrative distance for locally originated is 200, for
> RIP 120. RIP therefore wins.
>
> In case I've got the sequence figured out wrongly, comments are welcome.
>
> Ben
>
>
>
>
>
>
> On 9/26/07, Gregory Gombas <ggombas@gmail.com> wrote:
> >
> > I'm seeing the following quirk in a production network:
> >
> > BGP-->
> > RIP-->
> > RTRA----------RTRB
> >
> > Router A is directly connected to router B and is sending the same
> > routes via RIP and eBGP.
> > Router B is also redistributing the RIP routes into BGP (but filtered
> > from sending back to A)
> >
> > When you look at the route table on RouterB, it shows the routes as
> > RIP routes!
> > You would think the eBGP learned routes would be preferred because of
> > lower AD.
> > But when I look at BGP table it shows the route originated locally and
>
> > thus preferred over eBGP learned route.
> > When I clear ip route the route is then shown as a eBGP route in the
> > routing table and BGP route table does not show the locally originated
>
> > route!
> >
> > Just wondering if anyone else has seen this...
> >
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