Subject: Re: VLAN + bridging problems
To: Dobromir Montauk <email@example.com>
From: William Waites <firstname.lastname@example.org>
Date: 12/10/2002 02:50:00
>>> "Dobromir" == Dobromir Montauk <email@example.com> writes:
Dobromir> It's not. But my guess is that the NetBSD VLAN driver,
Dobromir> like the Linux driver, should strip off the VLAN tag
Dobromir> before doing anything else - for example forwarding the
Dobromir> packet through a bridge...
You are correct, that is exactly what's happening. In
sys/net/if_ethersubr.c the relevant function is ether_input(), around
line 703. The packet is bridged first, then the vlan header is
stripped off around line 754.
Dobromir> In Linux, supposedly, there's a special option to turn
Dobromir> this "feature" on/off. I was hoping NetBSD had the same
If we strip the vlan header off before bridging the packet, then
bridging under the vlans won't work -- you can't make a repeater out
of two NICs that will forward packets leaving the 802.1q header
As it is, there are four possible setups for a bridge:
- vlan and vlan as members of a bridge -- this works correctly because
vlan_input calls ether_input recursively after it has stripped the
header and neither parent interface is the member of a bridge.
- vlan and ether (not parent of vlan) -- this works correctly as long
as tagged packets are never recieved on the ether interface. If
tagged packets are recieved, an extra header gets tacked on.
- vlan and ether (parent of vlan) -- this will not work for the same
reason -- ether must recieve tagged packets.
- ether and ether -- this is the repeater scenario above
Your setup is the third one, no?
Basically the the third and fourth scenarios are mutually
exclusive. The configuration option you are asking for would be a flag
that would toggle between the two, correct?
At the moment it isn't clear to me how to do that without making
ether_input() start to look like spaghetti... But then again, it's
I suspect the reason that the switch vendors don't support this either
is to avoid having their code look like spaghetti also. Maybe Linus
doesn't mind ;)