I wrote the below in a rush and quality suffered. It is indeed riddled with errors.. Sorry about that.
Short answer. A does not have a link to B, but transits C. Diagram is really A---C----B---EBGP---D. I got a little confused by your diagram which came through garbled. Network 2.2.2.0/24 is reachable on B. Network 1.1.1.0/24 is reachable on B as well. The routing table in question is a routing table, not a BGP table and thus the next-hops are IGP next hops. In that case, A has to use C's 3.3.3.3 address as a next hop in all cases as this is the only path A has out of the network toward anything it does not directly connect to. Halabi's diagram on 149 might confuse some into thinking that A, B, C and fully meshed at the physical layer, when in fact the only meshing occurs via IBGP which is a logical mesh. A does not connect to C and Halabi's line in the picture is meant to indicate the logical IBGP connection, not a physical link. Pete At 08:27 PM 3/27/2002 -0500, Peter van Oene wrote: >Hi Hunt, > >A little cut and past here. For those reading along, it page 150 of version >1. > >Router A (SJ) has only 1 physical connection which is to router B with an >IGP next hop of 3.3.3.3. In this example, Halabi is describing the >relationship between IGP and BGP next Hops. 2.2.2.0/24 is likely learned >via the IGP and is reachable through via 3.3.3.3 which is the IGP next hop >toward router C. The same goes for 1.1.1.0/24 which again is reachable via >router C. Indeed, router A has only one path out of the network. In >reality, the network looks like this: > >A----B----C---EBGP--D > >A,B, and C are fully meshed with IBGP. Hence, A will only ever have one >IGP next hop since it has only one path toward other networks and must >transit router B. > >Keep in mind that you are looking at the Routing Table, not the BGP >table. These are quite different which is what Sam is trying to point out. > >What may be confusing you is that at first glance it looks like SF has a >direct link to SJ (A to C) when in fact it doesn't, and the line in the >diagram is really an arrow describing the logical IBGP connection. > >Hope that helps? > >Pete > > > >What I am confused it's the Routing Table of Router A, > > >Destination 192.212.1.0 /24 Next-hop 2.2.2.2 (Best Route inserted > >from BGP table) - cool > > > >Destination 128.213.1.0 /24 Next-hop: 1.1.1.1 (Best Route inserted > >from BGP table) - cool > > > >Destination 3.3.3.0 /24 Next-hop: Directly Connected via Serial > >0 - cool > > > >Destination 2.2.2.0 /24 Next-hop: 3.3.3.3 (why?? isn't this > >directly connected via IBGP, shouldn't it be directly connected?) > > > >Destination 1.1.1.0 /24 Next-hop: 3.3.3.3 (why?? shouldn't > >this have 2 routes, one via 3.3.3.3, and the other via 2.2.2.2?) > > > > > >Also, I thought that in such a scenario, one would want to make sure that > >every BGP Next-Hop can be reached via either IGP or static routes - However, > >Halabi says it's only needed for IBGP Next-hop, is it correct? > > > >Thanks, > >Hunt Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=39754&t=39704 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
