There appears to be a bug in the resolver in libc-5.3.12. When a program uses gethostbyaddr() to do a reverse DNS lookup and that returns a CNAME instead of a PTR, the gethostbyaddr returns "Host name lookup failure" instead of following the CNAME and returning the cannonical name or "Unknown host". Using libc-5.4.44 or glibc gives the correct lookup. The practice of having IN PTR records pointing to a CNAME is becoming more common as more people delegate subnets to customers. It is the reccomended way of handling reverse DNS for subnets in the O'Reilly "DNS & BIND" book. The fact that Linux libc-5.3 can't handle such records (which other OSes can handle) is breaking sendmail's spam blocking. One of the options is to deny mail from servers that don't have proper reverse DNS. There are mail servers out there that have a reverse DNS subnet delegated to them through CNAME pointers, and they can't send mail through Linux libc-5.3 based servers such as Red Hat 4.x. The "upgrade to Red Hat 5" isn't really a solution - I can't just turn off the server for a few days to upgrade and test everything. I think there needs to be a new libc package for Red Hat 4.x that fixes this bug. It appears to be fixed in the latest libc-5 - libc-5.4.44. If anyone is interested in this problem, I can send a little test program that checks for this bug. -- Chris Adams - [EMAIL PROTECTED] System Administrator - Renaissance Internet Services I don't speak for anybody but myself - that's enough trouble. -- PLEASE read the Red Hat FAQ, Tips, Errata and the MAILING LIST ARCHIVES! http://www.redhat.com/RedHat-FAQ /RedHat-Errata /RedHat-Tips /mailing-lists To unsubscribe: mail [EMAIL PROTECTED] with "unsubscribe" as the Subject.
