|walldns(8)||System Manager's Manual||walldns(8)|
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 188.8.131.52.in-addr.arpa showing 184.108.40.206.in-addr.arpa as the name of IP address 220.127.116.11, and a matching A record showing 18.104.22.168 as the IP address of 22.214.171.124.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.