BIND 9.10 can be configured to have response policies. That means that it can be configured to give responses that are different depending on the identity of the querying client and the nature of the query. To configure BIND response policy, you put the information into a zone file whose only purpose is conveying the policy information to BIND. A zone file containing response policy information is called a Response Policy Zone, or RPZ, and the mechanism in BIND that uses the information in those zones is called DNSRPZ.
The RPZ mechanism has not changed in BIND 9.10. The documentation in KB article AA-00525 (Building DNS Firewalls with Response Policy Zones (RPZ)is still almost current. What has changed in BIND 9.10 is that it is now possible to use as many as 32 separate RPZ files in a single instance of BIND, and that BIND is not significantly slowed by such heavy use of RPZ. Each one of those 32 policy zone files can specify policy for as many different domains as necessary. The limit of 32 is on the number of independently-specified policy collections and not the number of zones for which they specify policy.
In earlier versions of BIND in which RPZ was implemented, having more than one RPZ zone file required BIND to perform a separate lookup in each policy zone to see if there was a match. In BIND 9.10, the policy information is stored in a radix tree, in which simultaneous lookups across all policy zones can be performed in sub-linear time that is approximately proportional to the logarithm of the number of policy statements in the largest collection (RPZ zone).
The improved implementation of RPZ for BIND 9.10 was provided by Vernon Schryver and Paul Vixie. It is faster because it is O(log n) in the size of the policy and because it can look up several items of data in parallel. The new limit of 32 results from the use of a 32-bit bitfield to identify the policy zones that affect a query. Previous implementations of RPZ were O(n) rather than O(log n).
We said above that the existing documentation is "almost current". The reason it is not totally current is that DNSRPZ in BIND 9.10 additionally supports drop policies and triggers based on the query client's IP address. The new RPZ-CLIENT-IP trigger clause and its use with a DROP policy is documented in the BIND 9.10 ARM in section 188.8.131.52.
© 2001-2016 Internet Systems ConsortiumPlease help us to improve the content of our knowledge base by letting us know below how we can improve this article. If you have a technical question or problem on which you'd like help, please don't submit it here as article feedback. For assistance with problems and questions for which you have not been able to find an answer in our Knowledge Base, we recommend searching our community mailing list archives and/or posting your question there (you will need to register there first for your posts to be accepted). The bind-users and the dhcp-users lists particularly have a long-standing and active membership.ISC relies on the financial support of the community to fund the development of its open source software products. If you would like to support future product evolution and maintenance as well having peace of mind knowing that our team of experts are poised to provide you with individual technical assistance whenever you call upon them, then please consider our Professional Subscription Support services - details can be found on our main website.