---
name: "walldns"
section: "8"
platform: "linux"
package: "walldns"
version: "1:1.05-22"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/walldns"
---

# walldns(8)

a reverse DNS wall

## NAME

walldns - a reverse DNS wall

## DESCRIPTION

**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*.

## Configuration

Normally  **walldns** is set up by the [**walldns-conf**(8)](/walldns-conf/8.md) 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.

## Further details

**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.

## SEE ALSO

[walldns-conf(8)](/walldns-conf/8.md)

http://cr.yp.to/djbdns.html