10.6 A More Restricted Name Server
You may want to restrict your name servers even furtherstopping them from even trying to contact an off-site server if their forwarder is down or doesn't respond. You can do this by telling the server not to fall back to using the recursive resolution process if no forwarders respond: check the Do not use recursion box on the Forwarders configuration tab (see Figure 10-9). The terminology is confusing: this checkbox has nothing to do with the kind of query being sent to the forwarders. As we said earlier, a name server that's forwarding always sends a recursive query to its forwarders. What this checkbox determines is what happens after that recursive query is sent, which we discuss next . The BIND name server configuration syntax calls this kind of forwarding name server a forward-only server, which we think is a good name.
A forward-only server is a variation on a server that forwards. It still answers queries from its authoritative data and cache data. However, it relies completely on its forwarders; it doesn't try to contact other servers for information if the forwarders don't give it an answer.
The slave server contacts each forwarder only once, and it waits a short time for the forwarder to respond. Listing the forwarders multiple times directs the forward-only server to retransmit queries to the forwarders and increases the overall length of time the forward-only name server will wait for an answer from forwarders. You might want to consider listing the forwarders' IP addresses more than once for redundancy: if the first query to a forwarder is lost, the second might still get through and be answered .
However, you must ask yourself if it ever makes sense to use a forward-only server. Such a server is completely dependent on the forwarders. You can achieve much the same configuration (and dependence) by not running a forward-only server at all; instead, configure your hosts ' resolvers to point to the forwarders you were using. Thus, you are still relying on the forwarders, but now your applications are querying the forwarders directly instead of having a forward-only name server query them for the applications. You lose the local caching the forward-only server would do as well as the address sorting, but you reduce the overall complexity of your site configuration by running fewer "restricted" name servers.