Increase File Descriptor Limit For NAMED/BIND/DNS

BIND/NAMED is compiled with a hard limit of 4,096 file descriptors and sockets and as a result if you have alot of IP's on a server you may see the following errors in /var/log/messages.

socket: file descriptor exceeds limit (4096/4096)
could not listen on UDP socket: not enough free resource

To increase that limit, add the following:

ulimit -HSn 200000
OPTIONS="-4 -S 8096"

to:

/etc/sysconfig/named

and then run:

service named restart

Verify in /var/log/messages that you are no longer seeing those errors and also run:

service named status

...to ensure NAMED is running properly.