H.248 Network Redundancy

Network redundancy is achieved when the H.248 stack can be reached by at least two physical networks ports on the TMG. On the TMG800/3200, usually H.248 uses the mgmt port, but with the network redundancy feature it is possible to use the VOIP0/1 and ETH0/1 port combinations. For example if we use a VOIP0/1 combination, initially the traffic will go through VOIP0 and if a failure is detected then it will switch to using the VOIP1 port. The switch will be transparent for the MGC, in fact only the Ethernet switch will see the difference and it should adapt very quickly.

Technically speaking

When using the network redundancy feature, the H.248 stack will bind itself to a special VLAN tagged (802.1Q) interface that is routed (level 2 routing) to a physical port. The TMG-CONTROL software will monitor the link:

1. Ethernet link
2. Ping (ICMP echo) requests on a specified IP address

When either of the monitoring techniques finds a failure the routing will change to the next available physical port specified in the configuration. When a routing change occurs ARP broadcasts are sent on the new physical port so that the Ethernet switch adapts to the change.

Some additional steps are necessary in order to use this feature:

Installing vconfig on the TMG Host

This is only needed for TMG800/3200 that were bought before the H.248 network redundancy was advertised. You do not need to do this otherwise and you should skip this step.

You can check if you need to install the required package by typing the following in a terminal on the TMG host:

yum list installed vconfig

If the output is similar to the any of the following lines then you do not need to install the package since it is already installed:

vconfig.x86_64 1.9-3 installed

vconfig.ppc 1.9-6.tb1 @/vconfig-1.9-6.tb1.ppc

In the case you do not see this output, the host is missing a package for the feature to work correctly so we need to install it.

TMG has internet access

1. Install the package on the TMG unit:

yum install vconfig

TMG has NO internet access

1. Download package from telcobridges (http://download.distribution.telcobridges.com/TBLinux/updates/1/os/vconfig-1.9-6.tb1.ppc.rpm)
2. Upload package to the TMG unit. You can use Winscp to do a file transfer to the tmg.
3. Install the package on the TMG unit.

yum localinstall vconfig-1.9-6.tb1.ppc.rpm

Configuring the Switch

Since the network redundancy feature requires VLAN tagging, the switches where the physical ports are connected to need to be configured for H.248 network redundancy. Usually the switch configuration for VLANs is to specify which ports are part of the VLAN but it could also be to specify untagged ports (if the H.248 traffic needs to be untagged for the MGC).

Configuring System Virtual IP Interfaces

The next step is to configure a virtual IP interface that will encompass two physical ports. This is done in the web portal menu item: "System Virtual IP Interfaces". From there you can create a virtual IP interface for H.248 and specify:

1. VLAN Id
2. IP confiuration
3. Physical ports to use
4. Polling params

Configuring H.248

Now in the H.248 configuration you need to set the local IP field to the system virtual IP interface that was created for H.248. Then you just need to apply the configuration to complete the configuration.

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