Hi there,
There are a few ways that you can keep a multicast entry alive, but the all revolve around having some multicast traffic.
I would configure the router closest to the real time viewer to be permanently in the multicast group. There is an interface command "ip icmp join-group 239.x.x.x", this will make sure that the flow is always passed through to the router.
Also, to keep the flow alive, you can set a router (here I would use the one closest to the ip camera) to poll the 239.x.x.x address, thus creating the multicast traffic.
You can do this in 2 ways, either by setting the ip sla monitor to ping the multicast group every minute or so, or have a kron job do it. Personally, I would use the ip sla monitor,as I've never really had much joy with the kron scheduler.
Check out this link for more details:-
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hsla_r/sla_01h.htm#wp1048913
Basically, you'll be keeping the multicast stream alive between the router that connects to the camera and the router that connects to the viewer.
Have a go and let me know how it goes!
Best Regards,
LH
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