nsupdate increments the zone's serial number for you

redcricket@rpz-tx1-1-l:~$ dig +short rpz.red-cricket-blog.com soa @localhost
rpz-tx1-1-l.red-cricket-blog.com. csirt.red-cricket-blog.com. 1344659785 3600 900 2592000 7200
redcricket@rpz-tx1-1-l:~$ sudo /usr/bin/nsupdate
> server localhost
> update del rbc.red-cricket-blog.com.rpz.red-cricket-blog.com 300 CNAME redcricket-lnx.red-cricket-blog.com
> send
>
> quit
redcricket@rpz-tx1-1-l:~$ dig +short rpz.red-cricket-blog.com soa @localhost
rpz-tx1-1-l.red-cricket-blog.com. csirt.red-cricket-blog.com. 1344659786 3600 900 2592000 7200