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How to configure the voice VLAN appropriate to each site through profile files in a Cisco CallManager 4.x environment, which has Centralized Call Processing with Multisite

Core Issue

In a Cisco CallManager 4.x  environment with Centralized Call Processing with Multisite, there are no switches in the remote sites and the voice VLAN is different in the different sites. Look for a way to configure the voice VLAN appropriate to each location through profiles files.


There is no such way in the Cisco CallManager device pool configuration to associate a profile file(s) and also this cannot be achievable by only one Dynamic Host Configuration Protocol (DHCP)/TFTP server.

Given that:

  1. An IP Phone tries to download a phone-specific profile file from the TFTP server.

  2. If the phone-specific profile file does not exist, the phone tries to download a common profile file.

    For option 2, it is necessary to use a common profile file in which only one dot1Q VLAN ID can be specified by VLANSetting flag and only one operational VLAN ID can be specified by OpFlags, therefore you cannot configure multiple VLAN IDs by only one common profile file. There must be only one common profile file in one TFTP server because common profile file name is unique.

These steps are not ideal but theoretically possible:

The assumption is that there are four different sites and you want to assign different VLAN ID for each site by common profile file.  Complete these steps in order to achieve this:

  1. Deploy four independent broadcast domains , for example, a different IP subnet.

  2. Deploy one DHCP server and one TFTP server for each broadcast domain.  For example, you need 4 DHCP servers and 4 TFTP servers.

  3. Put a common profile file on one TFTP server.  For example, the common profile file is only common in a site.

  4. In each broadcast domain, apply appropriate packet filtering in the IP routing device(s) so that a DHCP discover from a phone does not go through to the
    other broadcast domains.

    The idea is to restrict DHCP/TFTP sequence within one broadcast domain, for example, all phones in one site can only access to one specific TFTP server in the same broadcast domain. Then phones in the site can download the same common profile file that specifies the same VLAN ID.

    In an optimized IP Telephony network, it is ideal to use minimum DHCP and TFTP Servers. The previous steps are only theoretical and not recommended in an ideal IP Telephony Network.

    Rather in an optimized IP Telephony network, IP addresses for telephones and PCs must be set up in different network segments. If DHCP is used to assign addresses, then a DHCP server for each network segment is normally needed. But, you can use a single DHCP server to assign both ranges of addresses if there are routers capable of DHCP relay in the IP network.

    Refer to Using One DHCP Server for Voice and Data Networks for more information.

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‎06-22-2009 04:37 PM
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