Secrets of configuring DHCP policies for Lync handsets alongside other vendors

By | 2012-06-21

After battling with a non-Microsoft DHCP server to get it to configure multiple vendors of handset I figured out some very useful undocumented ‘habits’ of Lync handsets which might help someone else…

1. Lync handsets (e.g. the Polycom CX600) use TWO vendor IDs during their DHCP requests

The first vendor ID that is used during negotiation of an IP address is “CPE-OCPHONE”. This is the legacy ID that was used during the OCS 2007 days. Despite being legacy it is actually the first one that appears on the wire. Knowing this if you are struggling with getting Lync handsets to do vlan tagging you’ll hopefully realise that CPE-OCPHONE is the vendor ID you need to be using in option 60 for the vlan tagging configuration policy in DHCP.

The second vendor ID used is the modern Lync handset ID, namely “MS-UC-Client”. This is the one you use in option 60 when you provide the configuration to the phones.

2. If you have to use a non-Microsoft DHCP management server (e.g. QIP) and you are in the middle of migrating from an IP-PBX (e.g. Alcatel) over to Lync but need to use the same voice vlans for both handset vendors, make life easy and use Vendor Class policies.

Using Vendor Class policies assigned to your voice networks means you can have multiple DHCP policies available on a single subnet. This way you can have non-voice clients that get a standard policy, and multiple vendor handsets that can get their own configuration sets. You could¬†configure each individual IP address to have a single DHCP policy and statically assign phones to pre-configured IPs, but that doesn’t scale and it’s horrible to deal with.

Microsoft use vendor classes, and for good reason, so make sure you do your best to configure your non-Microsoft DHCP to use them too. Having to use multiple vendors’ phones is a pretty rare thing so you may not be able to get much support from anywhere.

3. Get hold of a simple network hub and use this with wireshark on a laptop to monitor DHCP traffic. It’s much easier than guessing what settings are (or are not) working.

4. If your network switches support LLDP-MED for goodness sake use it!

LLDP-MED is so much easier to handle and can be assigned to all ports on a switch instead of having to assign a specific voice vlan for a specific port. That and if you can use LLDP-MED you will not need to configure the phone to know what vlan to use for tagging because the LLDP protocol will do that for you.

5. When you’re stuck with a non-Microsoft DHCP server, read this article¬†and this one from TechNet. The info you’ll need is there, they just haven’t really explained it too well.