DHCP multiple pools

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Aug 26th, 2008
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Hello all,

One short and simple (hopefully) question. Let's say I have two locations with phones and each has its own voice vlan with different scope. How do I configure DHCP server on CCM to lease the right address to the right phone, depending on the location? Hope it's clear...


goran pilat

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Overall Rating: 5 (3 ratings)
dezoconnor Tue, 08/26/2008 - 07:45
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Firstly, if your phones are on different sites and remote to the callmanager servers consider using a local DHCP server to provide resilence in the event of a WAN failure. If this is a large deployment consider using off box DHCP to reduce the load on the CUCM servers.

As for the config, create both your DHCP scopes, IP Address range, subnet, Default Gateway and option 150. On your switches in each location, configure your seperate voice vlans and if needed IP helper addresses. When an IP phone is plugged into each respective switch it should pick up the correct IP Address.

Jaime Valencia Tue, 08/26/2008 - 07:47
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configure separate pools and have each one have the range of IPs you're using on each vlan.

if you have

10.10.10.x / 24

10.10.20.x / 24

one pool per subnet, be sure to put an IP address under the interface VLAN and to take the IP's already in use from the pool



if this helps, please rate

Michael Owuor Tue, 08/26/2008 - 07:52
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Hi Goran,

To add to Darren and Java's good posts, here's some information on how this works (+5 for both you guys, by the way).

The DHCP message has a giaddr field (gateway address) which provides the DHCP server with information about the IP address subnet on which the client is to reside. If there is a device such as a router of switch that forwards the DHCP request using a helper-address, that router or switch includes its own IP address in the giaddr field.

The DHCP server identifies which DHCP address pool to use to service a client request by looking at the giaddr field of the DHCPDISCOVER broadcast message. It will match the DHCPDISCOVER with a DHCP pool that has the subnet that contains the IP address in the giaddr field.

Hope this helps.



goranpilat Tue, 08/26/2008 - 11:24
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Hi guys,

Thanks a lot for your great help, appriciate it. Also fiver for you, Michael, great explanation...

take care,


Michael Owuor Tue, 08/26/2008 - 11:44
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Thanks Goran, for your kind follow up, and allowing us the opportunity to help!




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