Identify and respond to vendor-specific information, Polycom-ssip 6100

Peter Rathlev peter at
Tue Sep 17 19:01:23 UTC 2013

On Wed, 2013-09-11 at 19:32 +0000, Kitterman, Scott wrote:
> I am trying to identify a VOIP conference phone, "Polycom SSIP 6100",
> vendor-specific information and reply with an option-128 string
> specifying the correct 802.1q vlan the Polycom should change to.

The DHCP server only replies with the options the client asks for. Your
Polycom device doesn't ask for option 128 according to the capture.

One reason a Polycom device will not ask for a VLAN via DHCP is if it
has already been told one via CDP og LLDP. Another is that you have
disabled VLAN discovery altogether.

> The device sends both option-60 and a option-125 (VSIO).  I believe I
> can identify and match option-60 but have had no luck identifying or
> responding to option-125.

Well, the options the clients sends and the options the server sends are
not supposed to mirror each other. The client uses a "special" option
(55) to request options from the server. The server would normally only
reply with the options set there. (You can alter this, but chances are
that the devices ignores options it didn't ask for.)

> I have attached a PCAP file of the Polycom rebooting, getting an
> address and send out a DHCP Inform.  Below I have what I believe to be
> key information in regard to the DHCP interaction of a INFORM and ACK
> followed by the dhcpd.conf.

I'd take a look at the phone and see what the VLAN menu says.


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