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Cisco IP Telephony Solution Reference Network Design
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Chapter 1 IP Telephony Deployment Models
Multi-Cluster Campus TFTP Services
When all the available bandwidth for a particular site has been used, you can provide automatic failover
to the PSTN by using a combination of the following two methods:
·
The route list and route group construct for calls across multiple Cisco CallManager clusters
·
The automated alternate routing (AAR) feature for calls within a Cisco CallManager cluster (For
more information on AAR, see the section on
Automated Alternate Routing, page 7-9
.)
Multi-Cluster Campus TFTP Services
Cisco IP Telephony devices rely on Trivial File Transfer Protocol (TFTP) to download the files required
for their proper initialization, configuration, and registration. The TFTP server is part of the
Cisco CallManager cluster and is responsible for creating and transferring configuration files. In a
single-cluster environment, all devices rely on a single TFTP server. The TFTP server address is
typically configured as option 150 in the DHCP server's scope.
In multi-cluster systems, it is possible to have a single subnet or VLAN containing phones from multiple
clusters. In this situation, the TFTP server whose address is provided to all phones in the subnet or
VLAN must service the file transfer requests made by each phone, regardless of which cluster contains
the phone. This centralized TFTP server, therefore, must have access to files created and managed by
other clusters.
To provide access to files in other clusters, each cluster's TFTP server must be configured to create and
manage configuration files on the centralized TFTP server's drive. To configure this file access, use the
alternate file location entry under each TFTP server's configuration (with the exception of the
centralized TFTP server's cluster).
Note
With Cisco CallManager Release 3.2 and later, Cisco TFTP servers cache the configuration files for the
IP phones in RAM by default. For those files to be written to a centralized TFTP server, you must disable
caching by modifying the following service parameters from their default values on each TFTP server
configured to write to the centralized TFTP server:
·
Enable Caching of Configuration Files: False (required)
·
Enable Caching of Constant and Bin Files at Startup: False (recommended)
If the TFTP server receives a request for a file that it does not have (such as a configuration file created
and maintained by the TFTP server in a different cluster), it will search for the file in a list of alternate
file locations. You have to configure the centralized TFTP server to search through the subdirectories
associated with the other clusters.
Example 1-4
Alternate TFTP FIle Locations
A large campus system is deployed using four clusters, and each cluster contains a TFTP server. In all
subnets, the DHCP scope provides the IP address of TFTP1 as option 150. Assume that TFTP1 is the
centralized TFTP server for this system of four clusters. The other servers, TFTP2, TFTP3 and TFTP4,
are each configured to write their configuration files to the following subdirectories on TFTP1's drive:
·
TFTP2's alternate file location is set to: //TFTP1/Program Files/Cisco/TFTPpath/TFTP2.
·
TFTP3's alternate file location is set to: //TFTP1/Program Files/Cisco/TFTPpath/TFTP3.
·
TFTP2's alternate file location is set to: //TFTP1/Program Files/Cisco/TFTPpath/TFTP4.