System information

Troubleshooting TCP/IP
Book Title
7-134
HSRP: Hosts Cannot Reach Remote Networks
Symptom: Hosts cannot reach hosts on remote networks. Routers in the network are running HSRP.
Table 7-18 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 7-18 HSRP: Hosts Cannot Reach Remote Networks
Misconfigured
aggregate-address command
The aggregate-address router configuration command allows BGP to specify a
summary address for one or more specific network addresses. For example, to
summarize the addresses 195.10.20.0 and 195.10.130.0, use the aggregate address
195.10.0.0.
Problems can occur under the following circumstances:
• The aggregate address summarizes addresses that are not in the router’s BGP
routing table.
In this case, a router is advertising networks to which it does not have a BGP
route. For example, a router is configured with the aggregate address 195.10.0.0
summarizing networks 195.10.20.0 and 195.10.130.0.
However, network 195.10.192.0 is in another autonomous system that is
inaccessible through the router. Traffic destined for network 195.10.192.0 will
be forwarded to the router, because it is incorrectly advertising a route to that
network (via the aggregate address).
• There are no individual networks configured (using the network router
configuration command) or routes in the BGP routing table to which the
aggregate address refers.
Step 1 Use the show running-config privileged exec command to view the
router configuration. Look for an aggregate-address command entry
associated with the router bgp global configuration command.
Step 2 Use the show ip bgp privileged exec command to view the addresses in
the BGP routing table.
Step 3 Make sure that the addresses summarized by the aggregate-address
command are all present in the BGP routing table.
Possible Problem Solution