In message <53281.1315691...@tristatelogic.com>, "Ronald F. Guilmette" writes: > > When called, res_query must be passed the base address of a buffer > (`answer'), and the maximum length of that buffer (`anslen'). Upon > return, res_query returns the count of bytes bytes actually used in > the target buffer (i.e. the response packet size) or else -1 for errors. > > Assuming that one wishes to call res_query in a manner that allows for the > largest possible response packet size, what size should the `answer' > buffer have, and what value should `anslen' have?
The maximum DNS message size is 65535 bytes. AXFR/IXFR are a series of messages. > I'm sorry to bother you all with this trivia question, but I have not > found any place where this value (max DNS packet size) is documented. > > Of course, at the dawn of DNS, the answer... for UDP response packets, > at least... was 512. But it appears to me that response packets sent > via TCP can be up to 1<<16 (64KB) in length, and I have no idea what, > if any limits might apply to EDNS packets sent via UDP. EDNS is theoretically 65535 bytes but it is recommended to use a smaller size even if your OS supports it. 4096 is common. > Regards, > rfg > _______________________________________________ > 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 -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org _______________________________________________ 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
