D.J. Heap wrote:
> I do resolve through my ISP but have never seen any DNS troubles with
> svn.collab.net traced back to them. I don't think I'm alone in
> suspecting there is (or has been) something flaky about svn.collab.net's
> DNS somewhere...
Actually, now that I walk through everything manually, there is something weird
(or at least suboptimal) about the setup. The root servers have the following:
> $ dnstracer -os . svn.collab.net
> Tracing to svn.collab.net[a] via A.ROOT-SERVERS.NET, maximum of 3 retries
> A.ROOT-SERVERS.NET [.] (198.41.0.4)
> |\___ M.GTLD-SERVERS.net [net] (192.55.83.30)
> | |\___ ns3.collab.net [collab.net] (64.151.90.204) Got authoritative answer [received type is cname]
> | |\___ ns2.collab.net [collab.net] (64.125.178.141) Got authoritative answer [received type is cname]
> | \___ ns1.collab.net [collab.net] (64.125.134.21) Got authoritative answer [received type is cname]
... same for other .net TLD servers...
> ns1.collab.net (64.125.134.21) svn.collab.net -> morbius.ch.collab.net
> ns2.collab.net (64.125.178.141) svn.collab.net -> morbius.ch.collab.net
> ns3.collab.net (64.151.90.204) svn.collab.net -> morbius.ch.collab.net
So since that answer is a CNAME, we have to start all over again from the
beginning and look up morbius.ch.collab.net:
> $ dnstracer -os . morbius.ch.collab.net
> Tracing to morbius.ch.collab.net[a] via A.ROOT-SERVERS.NET, maximum of 3 retries
> A.ROOT-SERVERS.NET [.] (198.41.0.4)
> |\___ M.GTLD-SERVERS.net [net] (192.55.83.30)
> | |\___ ns3.collab.net [collab.net] (64.151.90.204)
> | | \___ ns1.sp.collab.net [ch.collab.net] (208.185.179.200) Got authoritative answer
> | |\___ ns2.collab.net [collab.net] (64.125.178.141)
> | | \___ ns1.sp.collab.net [ch.collab.net] (208.185.179.200) (cached)
> | \___ ns1.collab.net [collab.net] (64.125.134.21)
> | \___ ns1.sp.collab.net [ch.collab.net] (208.185.179.200) (cached)
... same for other .net TLD servers...
> ns1.sp.collab.net (208.185.179.200) morbius.ch.collab.net -> 66.146.194.195
Note the difference between this run and the one above: there is only one name
server that is authoritative for morbius.ch.collab.net. This is bad for all of
the usual reasons (load balancing, single point of failure, etc.).
But it is also twice as long a chain to walk through for no good reason.
CNAME's are not what most people think they are. There is absolutely no reason
not to create a A record mapping svn.collab.net to 66.146.194.195; sure have the
PTR record point to the machine name (morbius.ch.collab.net), but you can have
as many forward (A) records as you want resolving to the same IP address. Even
if you run BIND. And there really isn't good justification for having yet
another nameserver (and a singleton at that) to be authoritative (especially
since it is an in-baliwick name).
John
--
John Peacock
Director of Information Research and Technology
Rowman & Littlefield Publishing Group
4720 Boston Way
Lanham, MD 20706
301-459-3366 x.5010
fax 301-429-5747
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Received on Sun Jun 26 03:44:51 2005