Hello, BIND Server Operators, ISC would like to make you aware of a recent change in the behavior of BIND that has been reported by one customer to have caused an operational issue in their environment due to its effect on the case of data returned in response to client queries.
The remainder of this posting explains the potential issue, which we believe will not affect most operators, but you should be aware of the potential in case you are one of those affected. This explanation is also provided in our Knowledge Base: https://kb.isc.org/article/AA-01113 -- The most recent maintenance releases of BIND (9.9.5, 9.8.7, and 9.6-ESV-R11) include a fix which we would like to highlight for your attention: 3645. [protocol] Use case sensitive compression when responding to queries. [RT #34737] This change was made to bring BIND into compliance with RFC 1034, which states: By convention, domain names can be stored with arbitrary case, but domain name comparisons for all present domain functions are done in a case-insensitive manner, assuming an ASCII character set, and a high order zero bit. This means that you are free to create a node with label "A" or a node with label "a", but not both as brothers; you could refer to either using "a" or "A". When you receive a domain name or label, you should preserve its case. Change #3645 was present in the precursor development releases for 9.9.5 et al but we received no reports of problems during the alpha and beta test periods. We still believe the change is correct in terms of compliance with the RFC, and BIND has been performing case-preserving compression for zone transfers for years without issue -- this change affects the data returned by regular queries -- however, we wish to inform you that a customer whose DNS data included both upper-case and lower-case representations of identical names experienced operational problems with client appliance devices that did not correctly implement the corresponding part of the paragraph above; that is, that domain name comparisons be done in a case-insensitive manner. Case was not previously being preserved by the server when compression was being used and as a result change #3645 had the effect in this customer's environment of causing a different reply to be returned by BIND 9.9.5 et al. In conjunction with the case-sensitivity of the misbehaving client devices, an operational issue was created by this mismatch. Operators encountering similar issues should be able to correct them by providing the exact case expected by client devices in their zone data (both in the domain names themselves and in references to those names in records of type NS, MX, SRV, CNAME, and other record types which use a domain name as their data.) Currently ISC are assessing whether the impact of this change justifies further measures or whether the change in BIND should stand as written. One key piece of information that would inform our decision is an estimate of the frequency of operational problems that might be caused by this change. So far we have no clear cues how to estimate that frequency based on our single report received. You can aid us by informing us of any issues encountered that you believe are related to this change in case preservation. Please send reports to bind9-b...@isc.org Michael McNally ISC Support _______________________________________________ Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
