Limiting an OSPF Database

I’ve got two routers, R0 and R1, with an OSPF adjacency between them. R0 doesn’t have much memory and he’s getting concerned that R1 is sending him too many LSAs.

R0’s OSPF database looks like this:

R0 has 7 LSAs, 6 of them from R1 (5.5.5.5)! That’s far too many for R0 to handle. We need to limit what R1 can send to R0, and we can do it with the max-lsa command. Cisco describes how it works here, so let’s experiment.

First, we specify the warning-only option:

Uh oh. We better put in some more stringent limits to make sure R0 doesn’t get overrun:

Without the warning-only option (and all other default values), R0 will drop its adjacencies for one minute should it maintain a 7th LSA in its database for over a minute. Let’s try it:

There’s a lot here, so let’s pick through it. At 48:11, R0 received a 7th LSA from R1. It generated a log message. One minute later (to the millisecond), R0 bounced all its interfaces and stopped sending or receiving any LSAs to/from its neighbors. Using default settings, R0 will stay down for 5 minutes before bringing its OSPF adjacencies back up. Once bringing them back up, if more than 6 LSAs exist in the database, a max-lsa log message will be generated and one minute later this interface-bouncing process will repeat. After going down five times (29 minutes later) the OSPF process will stay down until an administrator intervenes.

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