Troubleshooting Bgp; Strategies And Tools - HP 7102dl - ProCurve Secure Router Configuration Manual

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Troubleshooting Routing
15-164
However, different areas often use subnets from the same classful network,
and the range should only apply to the one area. You must then calculate
exactly which network bits the range of subnets have in common.
For example, if area 1 includes subnets 172.16.0.0 /20 and 172.16.16.0 /20, and
area 2 includes 172.16.32.0 /20 and 172.16.48.0 /20, the IP address range for
area 1 is not 172.16.0.0 /16. That summary would include subnets in the other
area. Rather, the address range for area 1 is 172.16.0.0 /19 (255.255.224.0). One
bit is removed from the prefix length to match both /20 networks. Similarly,
the address range for area 2 is 172.16.32.0 /19 (255.255.224.0).
See "Route Summarization (ABRs): Advertising a Link to One Area to Routers
in Another Area" on page 15-47 to review how to specify the range of addresses
in an area.

Troubleshooting BGP

BGP allows you a great deal of flexibility in setting a policy for exchanging
routes. However, these policies can be complicated to configure. The follow-
ing sections contain general tips for solving common problems.

Strategies and Tools

A BGP router might not send or receive the routes that it should for several
reasons:
It cannot communicate with a neighbor.
It is not authorized to transmit, or to accept, the routes in question.
View BGP neighbors to make certain the neighbor exists. (Enter show ip bgp
neighbor from the enable mode context).
If the router seems to be able to communicate with the neighbor, but it is not
receiving the routes that it should, you should examine BGP filters.
The clear, show, and debug commands will help you as you troubleshoot BGP.
show and debug Commands. Use the debug commands shown in Table
15-25 and the show commands shown in Table 15-26 as you troubleshoot the
router.