[CentOS] mounting nfs partition at boot.

This seems like another basic question because I always assumed that if 
I threw something in my /etc/fstab then it will be automatically mounted 
at boot time (unless I put in the 'noauto' option).

But my NFS partition isn't getting mounted, here's the excerpt from my 
/etc/fstab file, split on the whitespace so it's easier to read:

nfs_server:/exports/var/www
/var/www
nfs
rsize=8192,wsize=8192,timeo=14,intr

After the server comes up, I can do a simple, 'mount -a' and the 
partition is alive.  Do I need to use something like autofs?  I figured 
I wouldn't need that since there's no reason to unmount this partition.

Thanks,
Ajay