VLANs and routing

Ivan Voras ivoras at fer.hr
Thu Jun 14 01:29:32 UTC 2007


I have a question that's accidentally connected with VLANs, but I think
it's generally routing related.

The situation is :

machine1 VLAN 400 on fxp1 <-- network --> machine2, VLAN 400 on em0

The interfaces on both machines are called vlan400.

If I assign "normal" IP addresses on both ends, e.g. on
vlan400 on machine1 and on vlan400 on machine2,
everything's fine, I can ping each other through VLAN 400.

But the (somewhat weird) requirements are that the vlan interface on
machine1 shouldn't have assigned IP address, but the second one should.
So, I've removed the IP from vlan400 on machine1, and added a static
host route to via vlan400. Now, when I ping I get this:

PING ( 56 data bytes
ping: sendto: Invalid argument
ping: sendto: Invalid argument

The (excerpt from) route table with assigned IP address on machine1
(first case) looks like:
10.10/24           link#70            UC          0        0   1500  vlan400         00:30:48:8d:15:76  UHLW        1        3   1500
vlan400   1188

With the static route it looks like:         00:07:e9:d4:2b:39  UHLS        0        2   1500  vlan400

(the command is route add -host -iface vlan400 -llinfo)

The MAC address in the first case is correct - ...:76 is the MAC from
machine2. In the second case, it's not, it's the local MAC.

Is this kind of setup even supported?

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