Pete might be on to something, we're running plain old Debian boxes with BIRD, and I do recall having to mess about with ip_conntrack_max after noticing that we were rapidly filling up the table.
Gareth: Might be worth checking out BIRD for this. I've been running it for the last 6-8 months in a plain old OSPF+iBGP setup without a hitch. You don't get the nice JunOS-like CLI, configuration is all done by editing a file, but I'd be more than happy to offer advice and assistance if need be.
