Root denied login if networking down (on NIS/YP environment)

My 70+ hosts network (mixed CentOS, Fedora) uses NIS/YP. If networking is working OK, then no major issues occur, normally a trouble-less operation.

If connectivity is lost, either by a simple loose cable, or a major problem outside my reach, login operations depending on the NIS domain server hang - as expected.

But what I don't expect is that even login locally as root - it may produce a login prompt, but never get to the password prompt, hanging for ever. I get that way totally excluded from operating the machine even for simple troubleshooting. Only restoring connectivity brings back root and regular users.

My /etc/nsswitch file has the following order:

passwd:     files nis
shadow:     files nis
group:      files nis
hosts:      files nis dns

so I would expect that the local /etc/passwd and shadow files (where the correct credentials for the local root are OK) should be interpreted.

But it seems to keep looking outside for root's credentials - which are not to be found.

What am I missing here ?

Thanks!