RE: ospf database size - affects that underlying transport mtu might have

[Richard Vander Reyden via NANOG <nanog () nanog org>]

> This is a *single area* ospf environment, that has been stable for years.
> But now suddenly is having issues with new ospf neightbor adjacencies , which are riding a 3rd party transport 
> network 

I have seen this in the lab before, was related to the size of the LSA. 

> Anyone ever experienced anything strange with underlying transport network mtu possibly causing ospf neighbor 
> adjacency to be broken ?  I'm asking if the underlying 3rd party transport layer 2 network
> has a smaller mtu than the endpoint ospf ip interface have, could this cause those ospf neighbors to not fully 
> establish ?

You can check this with a ping of your mtu size set with the df bit set

> .and I'm also asking this if the single ospf area has grown large enough to cause some
> sort of initial database packet to be larger than that underlying 3rd party mtu is providing

If you have a large amount of routers in your area the LSA size will grow, we saw a problem in testing when we injected 
2000 prefixes into the area and the OSPF neighbour would not come up.  On a cisco router you can set 'buffers huge' as 
a work around.

Richard