Chaosnet support in BIND

Earlier versions (e.g. 9.3.1) of BIND (the standard DNS server on the Internet) only supported the Chaosnet class as a kludge to handle queries for server software version etc (see documentation). With the support for Chaosnet for ITS, it would be nice to support Chaosnet in DNS. It turned out to be fairly easy to add support for A (address) resource records.

The Chaosnet support is now included in the standard distribution of BIND (as of version 9.4).

The patches for BIND 9.3.1 (but you should update to the latest version!) can be downloaded here (and patches for the Fedora Core bind-9.2.5 source rpm can be found here, along with an updated spec file, and precompiled RPMs). Note: the patch also works for BIND 9.3.2.


The official documentation hasn't been updated yet, so here is some.

Textual format of A entries:
nameclasstypenet/domainaddress (octal)
MD.dom1 CH A CH-ADDR.dom2 3141
where net/domain is the Chaosnet (domain) where the address belongs (Chaosnet is a LAN, not an internet). This should be used both to see whether the address is useful for the client (which should be on the same net) and for address-to-name lookups corresponding to IN-ADDR.ARPA - in this case,
3141.CH-ADDR.dom2 CH PTR MD.dom1
Of course the "CH-ADDR" label can be just any legal DNS label, and dom1 and dom2 can be the same or not.

The binary resource record format is the net/domain name followed by the 16-bit address (as specified by RFC1034).

BIND config

To use the Chaos class in BIND, you need two things as a minimum: a zone declaration in your named.conf file, and the zone file itself. Unfortunately there is another complication: BIND enforces separation of classes, which forces you to keep IN and CH data for the same host in different files, and to wrap your Chaos zone in a view declaration. (Because of this, the occurrences of "CH" in the zone file example below are redundant.)

Example zone declaration in a view in named.conf:

view "chaos" CH {
  match-clients { any; };
  zone "" CH {
	  type master;
	  file "";
	  allow-update { none; };

Example contents of the zone file

@	SOA	localhost.	root.localhost. (	2005050702
						1H )
	NS	localhost.	

;; A Chaos A record has two parts:
;; - the domain/network of the address (Chaosnets are LANs - the address is local to the net),
;; - the (octal!) address itself
;; Without ending ".":s, the domain defaults to $ORIGIN which defaults to the zone name,
;; so "MD" means "" and "CH-ADDR" means ""
	CH	A    CH-ADDR 3141

;;; PTR records to find names from addresses.

Note that once you add the view for CH, you'll have to add one for the IN zones too. Wrap them all in, e.g.,

view "default" IN {
  match-clients { any; };


Write a DNS forwarder for Chaosnet, so you can pretend to have a Chaosnet DNS server on your ITS system. Need to check how the protocol was done in e.g. Symbolics systems.

© Björn Victor <>
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Senast ändrad: 24 november 2009.