
When applied, dnscache will accept a /-delimited list of IP address in $IP
and bind to each in turn. This allows one to have dnscache listen on, say,
external IP 1.2.3.4 which only client group A can reach, and, say,
internal IP 4.3.2.1 which only client group B can reach. Assuming 1.2.3.4
and 4.3.2.1 are on the same machine, instead of running two independent
dnscache instances on 1.2.3.4 and 4.3.2.1, one instance can bind to both
IP's and serve queries from the shared cache. Simply put 1.2.3.4/4.3.2.1 in env/IP.

http://danp.net/djbdns/patches.html
