Limiting DHCP Leases to only VoIP Phones

[Beth Verish]

We are running CM v7.1.3 with our publisher acting as the DHCP server on a VLAN.  We noticed that it will give out leases to computer systems along with phones. Is there any way to restrict the DHCP giving out leases to just VoIP phones registered in CM?  Thanks,  Beth

[Clifford McGlamry]

In general, you accomplish this by putting the phones into a separate voice vlan.  Best practice is that you don't put workstations in the same vlan with the phones.

The DHCP protocol could do this only if you set up reservations for the MAC's of the phones, and reserved all address space, but I'm not sure if you have that granularity of control in CCM.

You can only overcome so much if the design isn't right to start with.  You'd be better off fixing the switch configuration with a designated voice vlan for the phones.

[William Bell]

Beth,

I am with Clifford on this one (+5 Clifford) in that you will want your data and voice access VLANs to be logically separated. I would also add that running DHCP on the CUCM cluster is not best practice. But, if you must go this route, then you will first need to logically separate the networks. If, after the separation, the phones are in a different VLAN than the CUCM cluster, you can use 'ip helper' configurations on the default gateway for the IP phones. Point this helper to the CUCM server hosting the DHCP service. On the data access vlan, point them elsewhere.

If you can, I would recommend a separate voice and data access VLAN. I would also recommend separating your call control VLAN from all other voice and data VLANs (including voice access). Then run DHCP on a dedicated DHCP server (e.g. Infoblox or QIP or IOS router if you must). As Clifford noted, this may be easier said then done depending on your existing network design.

HTH.

Regards,
Bill