Detecting link state, FreeBSD

[Mahlon E. Smith]

On Thu, Nov 04, 2010, Ondrej Zajicek wrote:
> 
> 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.

Yep, exactly.  The static is then repropagated into the OSPF table, and
a remote area with the same setup acts as failover.


> Detecting a link state is crude, because there might be many
> other kinds of problems that does not change link state.

Agreed, although I'd maintain that in no case should a lack of link be a
valid condition for bird to think the interface is available, regardless
of the potential for other network problems.


> 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 completely missed that birdc had that capability.  Neat.


> 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).

That's great to hear.  I certainly didn't assume my patch would be
used, I've just always thought it more polite to try when requesting a
feature.  Thanks for your attention to it.

--
Mahlon E. Smith  
http://www.martini.nu/contact.html
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