Detecting link state, FreeBSD

[Ondrej Zajicek]

On Wed, Nov 03, 2010 at 07:39:48AM -0700, Mahlon E. Smith wrote:
> On Tue, Nov 02, 2010, Ondrej Zajicek wrote:
> 
> > 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.
> 
> Hmm, in this particular case, bird is currently responsible for managing
> routes that go out through that interface.  (Used for internet failover,
> on the external interface.)  With the link state down, the OSPF daemon
> was still reachable to the internal network, so the HELLO check doesn't
> help me unless the /internal/ interface dies, or the entire router does.

Although i agree with Joakim Tjernlund and others that link state change
detection is useful to get faster response to internal network
unreachability. I think that in your case you would need something
slightly different.

I understand that you have some (probably static) routes with gateway
accessible through given (external) interface and you want to detect
unreachability of the (external) gateway to add/remove that (static)
routes. Detecting a link state is crude, because there might be many
other kinds of problems that does not change link state. I would
suggest to use some shell/perl script that ping to the gateway and
according to its reachability it will enable/disable static protocol
(with routes using that gateway) in BIRD.

I plan to implement a link state change handling, but it will take some
time, it is definitely more complicated than the patch you sent (for
example, it should differentiate between administrative up/down and link
state up/down).

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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