Configuring rtp redundancy in a voice gateway

Unanswered Question
Apr 9th, 2009

I am looking for a solution to create a redundant path for rtp stream in our 3845 router with two GigabitEthernet interfaces.

Currently, both interfaces are plugged in to the different ports on a distribution switch and the second interface is configured as a backup interface for the first one. The idea was to send voice traffic to the backup interface when the main interface goes down. When it happened, we realized that our voice network is down b/c the backup interface did not have h323-gateway voip bind srcaddr command which can only be configured on one interface.

We want to keep the same IP address for obvious reasons.

I was considering creating a loopback interface and using ip unnumbered but it can't be used on Ethernet interfaces.

Any suggestions would be greatly appreciated.


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Paolo Bevilacqua Thu, 04/09/2009 - 13:29

You do not need unnumbered interface in order to bind voice packets to a loopback interface.

CHRIS CHARLEBOIS Thu, 04/09/2009 - 13:38

And it's good practice to bind the H323 to a loopback. You just need to make sure that the loopback address is advertised throughout the network, either via static routes, or by injecting that network into a dynamic routing protocol, like EIGRP or OSPF.

y-sapozhnikov Thu, 04/09/2009 - 13:39

Thanks for the quick reply

If I move the IP address from the Ethernet interface to the loopback, how the router would know where to send rtp packets? Would the "backup interface" command work without an IP address on the interface?

Paolo Bevilacqua Thu, 04/09/2009 - 13:42

Where to send is configured in dial-peer, it has nothing to do with interfaces.

You never use "backup-interface", just make a normal routing configuration.

CHRIS CHARLEBOIS Thu, 04/09/2009 - 13:46

No, you need to assign the loopback a new IP address with a /32 subnet mask. Leave the address on the ethernet as it is now, create a loopback interface, assign it a new IP address, and then bind the H323 to that address. Then you just need to make sure that every other device on the network knows a route to get to that loopback address.

y-sapozhnikov Fri, 04/10/2009 - 05:00

That's what I am trying to avoid b/c it will require a lot of configuration changes on other devices.

y-sapozhnikov Fri, 04/10/2009 - 04:59

That's the logical part of the routing decision. If I do not use backup interface, where would the router send a packet destined to the callmanager if the main ethernet is down?

y-sapozhnikov Fri, 04/10/2009 - 05:19

And that means assigning a new IP address to the second Ethernet interface. I was trying to see if there was a way to avoid this.

donovan222 Fri, 04/10/2009 - 05:42

INT1 /?

INT2 /?

Loopback /32

You will point you Dial-peers at the loopback and it will use INT 1/2 to route the calls to CCM. You will have to re-configure on your Gateway but you'll better off in the long run.


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