Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!gem.mps.ohio-state.edu!apple!sun-barr!texsun!pollux!smu!merlin From: merlin@smu.uucp (David Hayes) Newsgroups: comp.sys.next Subject: Re: host name resolution under 1.0 Message-ID: <15940@pollux.UUCP> Date: 25 Sep 89 17:50:18 GMT References: <6251@pt.cs.cmu.edu> Sender: news@pollux.UUCP Reply-To: merlin@smu.UUCP (David Hayes) Organization: Southern Methodist University, CSE Dept. Dallas, TX Lines: 44 In article <6251@pt.cs.cmu.edu> eht@f.word.cs.cmu.edu (Eric Thayer) writes: >[extra material deleted] > Names like Q.CS.CMU.EDU >you can abbreviate as Q, but it appears that if the abbreviation contains >a dot, it is assumed to be a complete name. Eric has found one of the design restrictions of the name server resolver routines. Given an entry in /etc/resolv.conf: domain dept.university.edu If a hostname has a dot in it, the resolver will conclude that the user has entered a fully-qualified domain name. If no dot is present, then the resolver will append the domain name from /etc/resolv.conf. This seems to be a problem, but for performance reasons, it really needs to be done this way. If you try to resolv "x.y", the resolver would be required to make multiple queries with varying bits of the current host's domain appended. Most of these would result in an error result from the name server, because the resulting host name "x.y.dept" does not exist. Since "x.y.dept" is not local, the query would have to go to the root servers, only to be told that there is no top-level domain "dept". The process would be repeated with all the other permutations of "x.y" and "dept.university.edu". The root servers just don't have the capacity to handle that load. At SMU, I do this. Each machine has an official name, such as "csvax.seas.smu.edu", my current host. It also has an alias, "csvax.smu.edu". The /etc/resolv.conf file says "domain smu.edu". Thus, I can get to any campus machine with its one-word name, even though the domain name structure is four levels deep instead of three. Here's the nameserver files: csvax.seas.smu.edu. IN A 129.119.1.5 csvax.smu.edu. IN CNAME csvax.seas.smu.edu. Of course, this only works as long as all machines within the higher-level domain (smu.edu, in this case) have unique names. You can easily see, though, how this could be used in the case of a five-layer domain name system. David Hayes School of Engineering Southern Methodist University merlin@smu.edu uunet!smu!merlin "Argue for your limitation, and, sure enough, they're yours." - Richard Bach