Configuring address and ports for JGroups

Question

When using JGroups, with a component such as Infinispan, it is possible to configure the ports and addresses that JGroups will use.

http://www.jgroups.org/manual/html/user-advanced.html

For example:

<UDP
        mcast_addr="${jgroups.udp.mcast_addr:228.6.7.8}"
        mcast_port="${jgroups.udp.mcast_port:46655}"
        ...

But here is what is confusing me. How can all members of the cluster all use the same port, addr?

I would have thought each member would have its own port and have to know the ports (and addresses) of the other members it needs to talk to?

Thanks

Answer 1

Multicast is a special address that can be used by multiple nodes to send/received data - think of it like 127.0.0.1, which is also available on most boxes with network installed.