You need to update a name server's root hints file.
FTP a copy of the most recent root hints file from ftp.rs.internic.net. It's called named.root, in the directory domain.
The root hints file, which tells a name server the domain names and addresses of the root name servers, doesn't need to be updated often. The "current" version dates to August 1997, and the file can be slightly out-of-date without causing adverse effects. Still, you should probably check every six months or so to see if it's changed.
If you do download a new root hints file, remember to change the name of the file to whatever you have defined in your zone statement for the root hints, and then reload the name server.
2.12.4 See Also
"The Root Hints Data" in Chapter 4 and "Keeping the Root Hints Current" in Chapter 7 of DNS and BIND.
BIND Name Server Configuration
BIND Name Server Operations
Delegation and Registration
Interoperability and Upgrading
Resolvers and Programming
Logging and Troubleshooting