VLANs, ifconfig, vconfig - Lilux-help

17 May 2005

Hi guys,

I'm trying to get some tests done here, but am butting my head
(granted, not at 100% power due to a cold) at the following:

I've got a Cisco L3 switch (C3550) that's supposed to handle several
links, among which a VLAN trunk.
Now I'd like to test the bloody setup to make sure I've got everything
right, but nicely, it's not even possible for the switch to ping it's
own IP addresses unless the connectivity of that port is up (i.e.,
there must be a machine at the other end responding properly).

For the 3 "classic" links, no problem, Laptop plus Knoppix did all
I needed - not so for the VLAN trunk.
Since Knoppix (3.8.1) doesn't seem to have VLAN support, I just
tried to use my own laptop (running Debian Sarge, kernel 2.6.11.7).
Copying the commands from another box handling a trunk (RedHat),
I tried to first set the MTU of the interface:

ifconfig eth0 mtu 1504 (the 4 bytes added for the VLAN ID)

That already got me an error message, apparently no values larger
than 1500 are accepted.

Now I decided to drop this, as I only need to get ping running,
which will not need the correct MTU size to work.

Next was the addition of VLANs to the interface:

modprobe 8021q

vconfig set_name_type DEV_PLUS_VID_NO_PAD
so far so good

vconfig add eth0 40
ERROR: trying to add VLAN #40 to IF -:eth0:- error: Invalid argument

This has me stumped - the exact same stuff works as advertised
on that RedHat box, I've got the exact same line in my doc (ex.
Linux Magazin network edition 3/2004 p. 13).
Same happens btw. if I specify /dev/eth0 instead of eth0.

Any ideas what's wrong here?

Greets & TIA, Eric