As with the previous NSKit release, the ypserv process provides support for machines which have more than one network address. When the machine maps are created, the Makefile creates a YP_MULTI_HOSTNAME entry in the map for any machine that has more than one address. This entry lists all the addresses for that machine. When the machine address is needed, an attempt is made to use the closest address on the list. See the ypserv man page for more details.
The determination of closest address is an arithmetic one and as such there is no check for address validity. For example, suppose that a multihomed machine has six IP addresses and only five of the interfaces on the machine are operating normally. Machines on a network that is not directly connected to this multihomed machine can receive the IP address for the down interface from ypserv. Thus, this hypothetical client can not reach the multihomed machine.
All addresses for a multihomed machine should normally be active. If a particular address or machine is going to be out of service, remove it from the NIS maps.