H.248 Network Redundancy

Revision as of 09:32, 19 July 2011

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 Ehternet 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.

In these cases the host is missing a package for the feature to work correctly so we need to install it:

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