In message <7737.1316035...@tristatelogic.com>, "Ronald F. Guilmette" writes: > > In message <7d9b265c-36bf-40c1-9012-ac0a96fb8...@sackheads.org>, you wrote: > > >On Sep 14, 2011, at 4:35 PM, Ronald F. Guilmette wrote: > > > >> Is there a rule that says how a resolver should behave in cases where > >> there is both an A record and also a CNAME record for the same FQDN? > >> Which one should take precedence, the A or the CNAME? > > > > > >RFC 1034, Section 3.6.2: "If a CNAME RR is present at a node, no other data > >should be present; this ensures that the data for a canonical name and its > >aliases cannot be different. This rule also insures that a cached CNAME can > >be used without checking with an authoritative server for other RR types." > > Thanks for the response John. > > So, um, the first part of that just says what people should not be doing > when they are constructing sets of RRs applicable to a given domain name. > > But we all know that, right? We know you are not supposed to put a CNAME > with other stuff for the same domain. > > The second part however seems to go more to my question, which is "What is > the resolver supposed to do when some knucklehead breaks the rules and puts > a CNAME in with some other stuff?"
You get indeterminate behaviour. > It sure _sounds_ like that second sentence is encouraging any & all people > who are writing resolvers, or other related tools, that they should ignore > any flotsam & jetsum that appear along side a CNAME. But is that encourage- > ment espressed anywhere as a "MUST"? The second sentence is saying if you have a CNAME record in the cache and don't have the type you are looking for you just follow the CNAME. If you don't do this the resolver would have to make a two queries. One to the authoritative server for the missing type which will normally result in the CNAME being returned and one for the target of the CNAME. > Not that I would want to deviate from common established practice... if > in fact ignoring flotsam & jetsum that appears with a CNAME is the common > practice. I'd just like to be able to defend the "rightness" of my code... > RFC-wise... in case anybody ever presses me and says "Why did you do THAT??", > you know, after I tell them that my code ignores flotsam & jetsum that appear > s > along side a CNAME. In this case you also have a CNAME that points to itself which is also a error condition. > 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
