Thanks for the explanation guys :) Just one more quick question, on the
"show ip bgp",
are the best routes indicated by an > or an *?
Regards,
Hunt Lee
Howard C. Berkowitz wrote:
> >Can anyone please explain to me what is the difference between the
> >command "show ip bgp" (or show ip bgp summary) and "show ip route bgp"?
> >I have read the BSCN book between page 348 and 352 many times, but I'm
> >still very confused. The book said "show ip bgp" displays BGP routing
> >table?? But I thought that should be "show ip route bgp". Please help.
> >
> >Regards,
> >Hunt Lee
> >IP Solution Analyst
> >Cable and Wireless
>
> You are dealing with two tables, at the very least. Some are
> conceptual or stored as part of other tables. Let me work through
> the flow.
>
> Incoming BGP updates, before filtering, go into the Adj-RIB-In
>
> After filtering, which is primarily on a per-peer basis, the
> remaining updates go into a BGP-only table called the Loc-RIB. This
> table contains all the BGP potential routes that passed acceptance
> filtering, and is router-wide. It also indicates which are the
> "best" BGP routes to a given destingation.
>
> "show ip bgp" displays the Loc-RIB.
>
> Next, all "best" routes from the Loc-RIB are sent to the main IP
> routing table, where they compete with potential routes from all
> other sources. "show ip route" shows the active routes to all
> destinations. "show ip route bgp" shows the subset of those routes
> that was learned from BGP.
>
> An example:
>
> BGP has two routes to 172.16.1.0/24 and to 172.16.2.0/24.
> It picks a best route to each. Let's say that has a next hop of
> 192.168.1.1
> Show ip bgp would show all four, with an asterisk on the two best.
>
> The two 172.16.1.0/24 and 172.16.2.0/24 routes, with a next hop of
> 192.168.1.1,
> are sent to the main routing table installation process.
>
> Assume that the router also has a static route with administrative
> distance 1 to 172.16.2.0/24. That has equal specificity to the second
> BGP route, but the administrative distance is more preferred.
>
> When you do a "show ip route", you will see routes to both
> destination, but with a static source to 172.16.2.0 and a BGP source
> for 172.16.1.0.
>
> If you do a "show ip route bgp", you will only see the route to
> 172.16.1.0, because that is the only active route with a BGP source.
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