FAQ: Problems With DNS Lookup
Sawmill only shows me the IP addresses of my visitors, even when I turn on DNS lookup. Why?
Your DNS server may not be responding, or may not know how to resolve those IPs.
(See Resolving IP Numbers for information about reverse DNS lookup).
Usually, this occurs because the DNS server can't resolve the IPs. The DNS server you're using needs to know about the IPs you're resolving. For instance, you can't use an external DNS server to resolve internal IP addresses, unless the external DNS server knows about them. Try using an internal DNS server, or another DNS server, if the first DNS server you try can't seem to resolve the IPs. It's useful to manually query the DNS server to see if it can resolve a particular IP; on most operating systems, this can be done with the "nslookup" command.