Troubleshooting OSPF
353
OSPF: insert route list LS ID 172.16.30.7, type 0, adv rtr
172.16.40.1
OSPF: Entered old delete routine
OSPF: running spf for summaries area 0
OSPF: sum_delete_old_routes area 0
OSPF: Started Building Type 5 External Routes
OSPF: ex_delete_old_routes
OSPF: Started Building Type 7 External Routes
OSPF: ex_delete_old_routes
This is a lot of information over a very short period. You can get an idea
of what the CPU goes through when there is a link-state change in a OSPF
network.
Typical Problems
Because of the great number of processes and calculations that the CPU has
to make when changes occur in an OSPF network, the router can become
overwhelmed with all the processing that has to be done. The bigger the
OSPF network, the more calculations have to be done, not to mention the
greater probability of changes that need to be propagated throughout the
network.
A general rule of thumb is to not add more than 100 routers per area, and
to not have more than 700 routers throughout the network. It is possible to
have smaller or larger networks, but the numbers here are given simply as a
guideline.
The more links that exist in a network, the greater the probability of insta-
bility. When a large network experiences instability, the routers have to
spend a great deal of time and CPU cycles processing link and route updates.
Another problem common to OSPF is wrongly configured wildcard masks
in the OSPF network statements. OSPF uses wildcard bits to specify the net-
works that should be advertised instead of using multiple network statements.
Either approach works, but be aware of the wildcard mask problems.
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