VLAN with intel adapter on XP

VLAN with intel adapter on XP
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Subject Author Date
VLAN with intel adapter on XP Gerald Vogt 03-12-2007
Posted by Gerald Vogt on March 12, 2007, 12:25 am
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I have setup two VLANs on a laptop with an PRO/100VE compatible
onboard adapter (latest proset/driver): 99 tagged and one untagged. It
connects to a switch port which is setup for VLAN 99 tagged and VLAN
10 untagged, default VLAN 10. The untagged VLAN connection works fine:
it gets an IP address via DHCP and can send and receive. The 99 tagged
connection however does not work. The packet counts on the connection
status shows that the connection does not receive any packets.

I have looked into what is happening with ethereal. The laptop
successfully sends the DHCP request through the 99 VLAN but the DHCP
offer comes in on the untagged connection only although it went
through the 99 VLAN and came from the 99 VLAN DHCP server. I turned on
monitormode on the adapter to capture the VLAN tags in ethereal:
ethereal shows that the DHCP offer received on the physical interface
does have the 99 VLAN tag. However, still the packet ends up on the
untagged virtual interface and not on the 99 VLAN connection.

I have a Linux box with the same VLAN setup, same port configuration
and it connects fine on both VLANs.

What else can cause this? Has anyone setup two or more VLANs with one
untagged and does it work properly? I get it to work only if I
configured both VLANs tagged on the laptop and the switch but then I
cannot plug in the laptop into a unmanaged switch without
reconfiguring it...

Thanks a lot,

Gerald


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Posted by Wrolf on March 14, 2007, 9:58 pm
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> I have setup two VLANs on a laptop with an PRO/100VE compatible
> onboard adapter (latest proset/driver): 99 tagged and one untagged. It
> connects to a switch port which is setup for VLAN 99 tagged and VLAN
> 10 untagged, default VLAN 10. The untagged VLAN connection works fine:
> it gets an IP address via DHCP and can send and receive. The 99 tagged
> connection however does not work. The packet counts on the connection
> status shows that the connection does not receive any packets.
>
> I have looked into what is happening with ethereal. The laptop
> successfully sends the DHCP request through the 99 VLAN but the DHCP
> offer comes in on the untagged connection only although it went
> through the 99 VLAN and came from the 99 VLAN DHCP server. I turned on
> monitormode on the adapter to capture the VLAN tags in ethereal:
> ethereal shows that the DHCP offer received on the physical interface
> does have the 99 VLAN tag. However, still the packet ends up on the
> untagged virtual interface and not on the 99 VLAN connection.
>
> I have a Linux box with the same VLAN setup, same port configuration
> and it connects fine on both VLANs.
>
> What else can cause this? Has anyone setup two or more VLANs with one
> untagged and does it work properly? I get it to work only if I
> configured both VLANs tagged on the laptop and the switch but then I
> cannot plug in the laptop into a unmanaged switch without
> reconfiguring it...
>
> Thanks a lot,
>
> Gerald


You have the correct idea of how 802.1q VLANs work, and how tagged and
untagged can be in principle mixed on the same port.

Unfortunately, the real world does not comply. E.g. Cisco
configurations use VLAN 1 to mean untagged - they cannot really handle
tagged VLAN 1. Etc. and so on. Lots of weirdness in different
implementations.

Punch line: for port based VLANs, set ports up for untagged (in a
given VLAN), or tagged.

And make sure that your switches have the same idea about spanning
tree being one tree per VLAN, or one for all. And be extremely careful
if trying to prune VLANs (having some VLANs only be on a subset of
your switches).

Wrolf


Posted by Walter Roberson on March 14, 2007, 10:21 pm
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>You have the correct idea of how 802.1q VLANs work, and how tagged and
>untagged can be in principle mixed on the same port.

>Unfortunately, the real world does not comply. E.g. Cisco
>configurations use VLAN 1 to mean untagged - they cannot really handle
>tagged VLAN 1. Etc. and so on. Lots of weirdness in different
>implementations.

I have never run into a Cisco IOS device or software version that
could not tag vlan 1, provided that the "native" VLAN was set to
something other than 1. (IEEE mandates that the native vlan for
a port be sent untagged.) There is a possibility that a PIX running
an early 6.3 software release might not have been able to create
a tagged vlan 1; if so then that's probably been fixed since.

Do you have specific examples of Cisco devices that could not tag
vlan 1? I've been following comp.dcom.sys.cisco for years and
do not recall anything like this mentioned.

Posted by Wrolf on March 16, 2007, 5:56 pm
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On Mar 14, 10:21 pm, rober...@hushmail.com (Walter Roberson) wrote:
>
> >You have the correct idea of how 802.1q VLANs work, and how tagged and
> >untagged can be in principle mixed on the same port.
> >Unfortunately, the real world does not comply. E.g. Cisco
> >configurations use VLAN 1 to mean untagged - they cannot really handle
> >tagged VLAN 1. Etc. and so on. Lots of weirdness in different
> >implementations.
>
> I have never run into a Cisco IOS device or software version that
> could not tag vlan 1, provided that the "native" VLAN was set to
> something other than 1. (IEEE mandates that the native vlan for
> a port be sent untagged.) There is a possibility that a PIX running
> an early 6.3 software release might not have been able to create
> a tagged vlan 1; if so then that's probably been fixed since.
>
> Do you have specific examples of Cisco devices that could not tag
> vlan 1? I've been following comp.dcom.sys.cisco for years and
> do not recall anything like this mentioned.


Yes. What I should have said is that by default Cisco IOS devices use
VLAN 1 to refer to untagged packets (native VLAN), but can be
configured to use another number to refer to it, and then VLAN 1 will
refer to packets tagged as VLAN 1; and that this is confusing and
leads to configuration errors. ;-P

Which is why I still tell people to avoid using VLAN 1.

Try

http://scry.wanfear.com/~greear/vlan/howto.html

for some hands on type info.


Posted by Gerald Vogt on March 15, 2007, 1:57 am
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Wrolf, thanks for your answer.
> Unfortunately, the real world does not comply. E.g. Cisco
> configurations use VLAN 1 to mean untagged - they cannot really handle
> tagged VLAN 1. Etc. and so on. Lots of weirdness in different
> implementations.

Sure. But after a few more tests I am pretty sure that the packets
arrive correctly on the laptop, i.e. all packets in VLAN 99 are
correctly tagged while the packets on the other VLAN are untagged. Still
the packets with the 99 tag won't make it to the VLAN 99 interface but
end up on the untagged interface instead. This does not look like
weirdness to me but rather a bug.

"weirdness" would be if the intel would except untagged packets to have
some VLAN 0 or 1 tag instead of being untagged and thus would discard
it. But instead all tagged incoming traffic ends up on the untagged
interface while all outgoing traffic which goes through the tagged
interface is correctly tagged.

> Punch line: for port based VLANs, set ports up for untagged (in a
> given VLAN), or tagged.

Yes. Seems to be the only way to get this working at the moment. The
switch handles the untagged/tagged mix correctly as it works with my
Linux box...

> And make sure that your switches have the same idea about spanning
> tree being one tree per VLAN, or one for all. And be extremely careful
> if trying to prune VLANs (having some VLANs only be on a subset of
> your switches).

Well, currently it is only a single switch... ;-)

Gerald

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