I had

hosts:      files nisplus nis dns

in /etc/nsswitch.conf. Before glibc-2.3.6-3, I had no problem looking up
external hostnames. After upgrading to glibc-2.3.6-3, I got

bash-3.00$ wget  http://www.kernel.org/pub/
--08:42:15--  http://www.kernel.org/pub/
           => `index.html'
Resolving www.kernel.org... failed: No such file or directory.

I had to use

hosts:      files dns

in /etc/nsswitch.conf. It looks like the new glibc treats

hosts:      files nisplus nis dns

as

hosts:      files nisplus nis [NOTFOUND=return] dns

BTW, I am not running YP.