91e62454_munin_conf___Munin__Default_value
[Directive] local_address [Explanation] Sets the local IP address that munin-update should bind to when contacting the nodes. May be used several times (one line each) on a multi-homed host. [Required] No [Default value] 
Should default to the most appropriate interface based on routing decision, if you don't set it explicitly.
munin.conf – Munin
Default value