Portmap by default listens to all IP addresses. However, if you are not providing network RPC services to remote clients (you are if you are setting up a NFS or NIS server) you can safely bind it to the loopback IP address (127.0.0.1)
<Yes> OR <No>

Maybe I'm slow or something but I really hate this prompt in debian. Which is accompanied by the installation of portmap. Seems like you need a degree in english logic to figure out what you need to select. If you run NFS and NIS and are Confused the hell out by this prompt just select NO.

UPDATE: Just because you select NO doesn't mean that debian will actually not bind RPC to portmap. You might want to run dpkg-reconfigure portmap again and make sure it did the right thing.. I got a nasty surprise the day after .. when 2 of the NFS servers stopped mounting. Filed bug report