Detecting link state, FreeBSD

[Ondrej Zajicek]

On Thu, Nov 04, 2010 at 08:25:34AM -0700, Mahlon E. Smith wrote:
> > 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.

If you do not have redundancy, it is usually better to keep static
routes installed even if the gateway is temorarily unreachable - if such
routes are removed, packets for that destination are routed using less
specific route (like default route), which is usually unexpected,
useless and causes route loops. If you keep the routes, the packets for
that destination are discarded with appropriate ICMP message
(destination unreachable). So definitely, it should be configurable
behavior.

BTW, there is one corner case when route to interface with link down
is valid and reachable - if you have one-way link (and asymmetric
routing).

-- 
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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