problem with dhcp setup

Frank Bulk frnkblk at
Tue Jun 19 14:24:18 UTC 2007

I saw a broken DHCP client in some VBricks I deployed at a previous job.

We were setting these up for non-static deployment across campus and for
the life of me I couldn't make it work. So I connected to the serial
interface and learned that the gateway and subnet mask weren't correct -- in
fact they seemed semi-random. I then tried the VBrick unit against a test 
Win2K box on a separate subnet it worked just fine!

Certain that ISC's DHCP server was in a good shape, I whipped out Ethereal
to look at the packet exchanges of both Win2K's DHCP server and ISC. The
DHCP request from the V-Brick asked only for an IP address -- not even a
subnet mask! So ISC's DHCP server wasn't handing it out.  And Win2K was
providing it, unannounced.

I contacted VBrick tech support and their response was that they only tested

against Windows 2000's DHCP server, none other.  I had a difficult time 
convincing the tech that this was a bug with their product.  When I left 
that job a year later VBrick had still not addressed the bug.

To mitigate the problem I found an option in ISC's DHCP to give out the
mask and gateway anyways.


-----Original Message-----
From: dhcp-users-bounce at [mailto:dhcp-users-bounce at] On Behalf
Of Simon Hobson
Sent: Tuesday, June 19, 2007 1:49 AM
To: dhcp-users at
Subject: Re: problem with dhcp setup

At 12:20 -0400 18/6/07, John Jason Brzozowski (CISSP, RHCT) wrote:
>So if a client requests no options, the ADVERTISE/REPLY will contain no
>options at all?
>Just because a client does not request options does not absolutely indicate
>that the client does not know how to handle the same.

If a client doesn't request an option it needs then it's broken and
there should be no expectation of it working ! It should not be down
to one piece of software to second guess what someone else broke and
fix it for them. While most clients seem reasonably 'sane', we have
come across a few which are broken in very ingenious ways - how about
one that doesn't ask for a default gateway but as well as this will
not accept a lease that is less than 2 years long ?

There are however a handful of options (address, subnet mask, gateway
I think) that are automatically sent even if the client doesn't
request them.

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