How do I allow Multicast packets over IPSec Site-to-Site VPN?

Issue:

We have 2 sites connected to a PBX at the main site per IPSec Site-to-Site VPN. 
Paging works through multicast packages, but they do not pass through the vpn. The phones are connected via the VPN from the other site. 
How do I set up routers so that they can display phones on the VPN?

Solution:

The usual IPSec Site-to-Site tunnel can not do this.

The VTI interface can transmit multicast traffic in a VPN tunnel. (VIT interface must use site-to-site VPN)

(1) Select "VPN Tunnel Interface" for the VPN connection

(2) Go to Configuration> Network> Interface> VTI> click on Add VTI interface.

It has support for IGMP (multicast) function. 

KB-00176