Cross site replication is configured using JGroups subsystem <relay/> and <remote-site/> elements to define sites and multicast relay routes between sites.

Looking at a site/route configuration as a graph of nodes and edges, xsite only works if this graph is totally connected (i.e. every site has a defined direct route to every other site). This is because <site name> -> <site id> mappings are assigned per node, with no agreement on what is happening at other nodes.

For example, this configuration works:

<relay site="LON">
<remote-site name="NYC" .../>
<remote-site name="SFO" .../>
</relay>

<relay site="NYC">
<remote-site name="LON" .../>
<remote-site name="SFO" .../>
</relay>

<relay site="SFO">
<remote-site name="NYC" .../>
<remote-site name="LON" .../>
</relay>

but this configuration does not:

<relay site="LON">
<remote-site name="NYC" .../>
<remote-site name="SFO" .../>
</relay>

<relay site="NYC">
<remote-site name="LON" .../>
</relay>

<relay site="SFO">
<remote-site name="LON" .../>
</relay>