Detecting link state, FreeBSD

Joakim Tjernlund joakim.tjernlund at
Wed Nov 3 10:28:05 CET 2010

> On Tue, Nov 02, 2010 at 11:00:39AM -0700, Mahlon E. Smith wrote:
> >
> > I'm running bird 1.2.4 on a series of FreeBSD OSPF routers.
> >
> > Had a backhoe go through some fiber this morning (really), and was
> > surprised to find that bird didn't update routes automatically.
> ...
> >
> > I don't see anything else to add or modify in the config for checking
> > interface status -- did I miss something?  My anticipated behavior would
> > be that a link down would perform a route update.
> Hello
> BIRD currently does not check or use link up/down state. OSPF routers
> generally check reachability using HELLO packets, not by reported link
> state, although sometimes this is also implemented. Drawback of HELLO
> protocol (to check reachability) is that it has some timeout to find
> out that the neighbor became unreachable. By default, it is ~ 40
> seconds, But it is possible to configure it to < 10 seconds (see
> hello/wait/dead interface options).

I think BIRD really should check link state. Changing HELLO < 10 secs
isn't going to make it much better and will also increase load and network


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