walldns - a reverse DNS wall walldns is a reverse DNS wall. It accepts iterative DNS queries for in-addr.arpa domains from hosts around the Internet, and supplies generic responses that avoid revealing local host information. For example, walldns provides a PTR record for 4.3.2.1.in-addr.arpa showing 4.3.2.1.in-addr.arpa as the name of IP address 1.2.3.4 , and a matching A record showing 1.2.3.4 as the IP address of 4.3.2.1.in-addr.arpa . Normally walldns is set up by the walldns-conf (8) program. walldns runs chrooted in the directory specified by the $ROOT environment variable, under the uid and gid specified by the $UID and $GID environment variables. walldns listens for incoming UDP packets addressed to port 53 of $IP . It does not listen for TCP queries. walldns rejects inverse queries, non-Internet-class queries, truncated packets, packets that contain anything other than a single question, queries for domains outside in-addr.arpa , and request types other than A, PTR, and *. walldns does not include NS or SOA records with its responses. walldns uses TTLs slightly over one week. walldns-conf(8) http://cr.yp.to/djbdns.html