>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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