Edit the file /etc/munin/munin-node.conf
Add an 'allow' line with the ip of the server.
It must be a perl regular expression because the Net::Server perl module which munin depends on doesn't understand CIDR-style network notation. You must include an allow line for every munin server allowed to connect to this client.
allow ^127\.0\.0\.1$ allow ^192\.168\.8\.204$
Start the munin-node service (on debian, /etc/init.d/munin-node start)
You may wish to view an example munin-node.conf.