"Martin A. Brown" <martin@xxxxxxxxxxxxxx> wrote on 06/13/2006 06:48:30 AM:
> This might very well be Linux-specific behaviour. I would encourage
> you to read the iproute2 documentation and compare the output of "ip
> address show" with your expectations.
You're talking about two different things.
If you have a route to get there, all addresses on a host,
whether the interface is down are not, are usable. This was true
on BSD systems 24 years ago.
Linux ARP uses a "weak end-system" addressing model by default,
meaning that Linux ARP will answer requests for local addresses
received on an interface other than the one that has the address.
The "strong end-system" addressing model used by BSD systems will
only answer ARP requests on the same interface as the address.
This allows Linux to "have a route" to back-side network
addresses for directly attached networks without running a dynamic
routing protocol. On (at least older) BSD systems, you'd have to
explicitly include a route, or run RIP, OSPF, or whatever to get
a route to the downed link. The address is always there, but you
might not have a route to it (unless you add one) on a strong
end-system model host.
In both cases, the hosts will receive and respond to packets
for any local addresses, no matter what interface the packets are
received on.
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