Very Computer

by **Javier Henderso** » Sun, 23 Nov 1997 04:00:00

Greetings,

I'm running 2.2.5-RELEASE, and the system has one Ethernet
interface with several IP addresses.

Up until now, all the secondary addresses were on the same
subnet. I recently added a secondary address on a different subnet,
which is of course present on the same wire, and while the new address
is reachable from other hosts, I see kernel complains about the
default gateway for the new address being on a different subnet.

It would appear that when there are packets that need to go to
an address in the same subnet as the new secondary address, then
initial ARP is done by the primary address, the kernel complains, and
eventually the ARP is done by the corresponding secondary address.

I read the docs on IP aliasing, I didn't see any restrictions
mentioned about all the secondary addresses having to be in the same
subnet as the primary.

Just thought I'd mention this, in case someone else has seen
this behavior.

-jav

by **J Wuns** » Tue, 25 Nov 1997 04:00:00

> I read the docs on IP aliasing, I didn't see any restrictions
> mentioned about all the secondary addresses having to be in the same
> subnet as the primary.

They aren't restricted, and it's easy to figure out that there was no
such thing like `virtual hosts' in mind (this was something rather
unknown by that time), but actually to ease the transition of a
machine between different networks. (That's why you need the rather
unusual `netmask 0xffffffff' iff the alias is in the same network
range as another address.)

I'm operating a number of machines with one interface in different IP
networks myself. If it doesn't work for you, something else must be
broken, but that's hard to guess unless you describe your setup in
better detail.

--
cheers, J"org

Never trust an operating system you don't have sources for. ;-)