[quagga-dev 4352] Strange behaviour in OSPF on 0.98.5

Len Sorensen lennartsorensen at ruggedcom.com
Mon Sep 11 15:06:10 BST 2006

While trying to do some testing of quagga and our routers ability to
handle a lot of routes we saw a strange behaviour from ospf in quagga

We setup two routers connected to each other and one subnet behind each
router.  We added 5000 static routes to each router pointing to
addresses on the subnet behind the router.  We then started quagga and
within about 2 minutes the routes had been learned by both routers.  We
then tried it while the routers were handling some extra traffic at the
same time, and OSPF never stabalized or managed to learn the routes of
the network.  tcpdump showed that packets were being exchanged between
the two OSPF daemons, but it seemed like they never finished, they just
kept repeating the routes.  If we then deleted the static routes while
OSPF was trying to stabalize, it kept exchanging route information even
after all the static routes had been deleted from both routes.  tcpdump
stil lshowed packets were continuing to be sent about the routes which
no longer existed, making it appear that the two OSPF daemons were
continuously telling each other about the same routes, which no longer
existed on either router.

We only have a 266MHz Geode GX1 processor, but even that should be able
to learn the routes and stabalize.  I would have thought that it would
do so within 5 or 10 minutes, but instead it just kept repeating what
appeared to be the same sequence of packets, without ever learning any
routes (lots of potential routes appeared to be going into the database
on OSPF with ages increasing, but never got added to the routing table
of the system).

Any idea what could be causing this behaviour where with no cpu load it
manages to work, but with a bit of extra load it fails to work?
Reducing to 1000 static routes per router makes it work perfectly fine.

Any idea what to look at to debug this?

Len Sorensen

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