Reverse DNS for

In Cambridge, the largest RFC 1918 address block,, is divided in two. The bottom half,, is for institution-private usage and is not routed on the CUDN. The top half,, is CUDN-wide private address space. (The Cambridge IP address ranges page has more information.)

This page describes how we have set up the zone for convenient sharing between institution-private and CUDN-wide private uses. There are some notes on how to configure this in BIND in our sample configuration for stealth secondaries.

Our central DNS servers provide reverse DNS for this address space using two zones. The zone contains 128 DNAME redirections corresponding to the top half,, and there are no DNS entries for the bottom half, The DNAME redirections point into the zone which contains the PTR records for the CUDN-wide private host registrations. Institutions which running their own DNS stealth-slave servers and which are not using are advised to slave both of these zones.

If you are responsible for an institution which is using, you should set up your own zone, with whatever PTR records you require for your part of the address space. For the top half of the address space, you should set up DNAME records just like our version of the zone. You should secondary so your name server has a local copy of the DNAME targets.

The easiest way to set up the 128 DNAME records in the top half of is to put the following directive in your zone file:

$GENERATE 128-255 $ DNAME $