since there is no version on the post
open the appropriate OS guide
Maintain and Operate Guides
http://www.cisco.com/en/US/products/sw/voicesw/ps556/prod_maintenance_guides_list.html
go to CLI commands and look for set network failover
Notice support depends on version and server brand (again, none of that on the post) so if you need more info look on CCO the release notes.
HTH
java
if this helps, please rate
HTH
java
if this helps, please rate