Frame Tagging

George Sexton georges at
Thu Aug 1 20:22:54 UTC 2013

> -----Original Message-----
> From: at
> [ at] On
> Behalf Of Ted Lemon
> Sent: Thursday, August 01, 2013 1:14 PM
> To: Users of ISC DHCP
> Subject: Re: Frame Tagging
> On Aug 1, 2013, at 5:17 PM, George Sexton <georges at>
> wrote:
> > First, since we've never had an interaction before, and I asked a
> pretty
> > reasonable question, that was well documented (complete, appropriate
> config
> > included, non-demanding or needy), I'm really at a loss to understand
> > people's attitude.
> You're talking to a list, not to a person.   The first step is not to
> personify it.   Nobody is responsible for answering, so people answer
> if they have the answer on the top of their head when they read the
> list, and don't answer if they don't.

And I'm responding to a list, and not a person. Obviously not everything I
said was directed at you personally.

Steven Carr's response was unhelpful, brusque, and basically had an
attitude. Putting the word please in a sentence doesn't make it polite. It
wasn't warranted.

> I was trying to be helpful; I'm sorry you took it as "copping an
> attitude."   Teach a person to fish, etc.   I asked that question to
> get a sense of what you'd thought of already.

Before I posted, I did a lot of research on the internet, read the man page
for dhcpd about 50 times, tried about 100 different configurations.

> The first thing I would do to debug this is to use a switch that takes
> tagged packets in one port, and puts untagged packets on the VLAN you
> want to configure out another port.   If that fixes it, then you're
> done, unless you really want to spend a lot more than 27 hours diving
> into the code!

The problem is that DHCP is seeing the packets come in on both the VLAN
tagged interface, and the regular interface, and responding on both. This
response on both the tagged and untagged interfaces is getting sent back to
the clients, causing weird things to happen.

I'm just not sure how I can use a switch (assuming I had one that capable)
in the manner you suggest.

I suppose what I could do is configure a 2nd NIC in the server, and
configure a switch in the manner you suggest. Put the tagged packets out a
different port, and connect that port to the 2nd physical NIC.  Then, on the
Linux server, get rid of the VLANs.

I don't suppose you have any suggestions for switches I could get cheap,
used that would have this capability?

> This is a question I actually would not have known how to answer a
> month ago-it's a fairly obscure topic for many of us, I suspect.

I've done networking for a long time, and never tried to use VLANs before. I
bought some wireless access points that had it, along with the ability to do
multiple SSIDs and I thought it would be a neat way to segment my wifi

It would be really nice if dhcpd were doing the right thing here...

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