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Multicast over TCP or UDP or whatever else

My Server and Client run both on Linux.
The Server broadcasts multicast, the Client listens multicast.

My Client has to migrate to another site,
and unfortunately multicast is not allowed between the two sites :-(

How to convey multicast between the two sites?
Through TCP or UDP?
What about latency?


Current: Server and Client on the same site

----------    ------------
| Server |    |  Client  |
| sends  |    | listens  |
|multicst|    | multicast|
|  IP1   |    |   IP2    |
----------    ------------
    |              |      
    |     LAN      |      
    ----------------      
         |                WAN              
         ---------------------------....

Future: Server and Client, each one on a different site

----------    ------------      ------------
| Server |    |          |      |new host  |
|        |    |          |      |for Client|
|   IP1  |    |          |      |   IP3    |
----------    ------------      ------------
    |              |                 |  
    | LAN of site1 |                 |  LAN of site2
    ----------------                 ----------...
         |                WAN              |
         -----------------------------------

I use the multicast channel: 224.1.0.1:6666

I received an answer about router configuration (GRE),
but I am afraid one of the network teams may be reluctant
because the transmission should not be broken during the working day
and I suppose changing a router or just changing its configuration may break the transmission
Is there other solutions? for instance based on Linux kernel features?