Re: Unexpected DNS responses

[Mark Andrews <Mark_Andrews@isc.org>]

> When doing a DNS query at Apple, I'm seeing strange results.
> 
> A query for the address record for login.oscar.aol.com reveals that it is 
> an alias for login.glogin.messaging.aol.com. The address for 
> login.glogin.messaging.aol.com is also given: 64.12.200.89.
> 
> >[chesh7:~] cheshire% dig -t a login.oscar.aol.com
> >
> >; <<>> DiG 9.2.2 <<>> -t a login.oscar.aol.com
> >;; global options:  printcmd
> >;; Got answer:
> >;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 5932
> >;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 2
> >
> >;; QUESTION SECTION:
> >;login.oscar.aol.com.           IN    A
> >
> >;; ANSWER SECTION:
> >login.oscar.aol.com.    123     IN    CNAME login.glogin.messaging.aol.com.
> >login.glogin.messaging.aol.com. 10 IN A     64.12.200.89
> >
> >;; AUTHORITY SECTION:
> >glogin.messaging.aol.com. 98    IN    NS    mtc-gdns008.ns.aol.com.
> >glogin.messaging.aol.com. 98    IN    NS    dtc-gdns008.ns.aol.com.
> >
> >;; ADDITIONAL SECTION:
> >mtc-gdns008.ns.aol.com. 223     IN    A     64.12.182.88
> >dtc-gdns008.ns.aol.com. 215     IN    A     205.188.139.88
> >
> >;; Query time: 8 msec
> >;; SERVER: 17.128.100.10#53(17.128.100.10)
> >;; WHEN: Tue Dec 14 11:38:01 2004
> >;; MSG SIZE  rcvd: 177
> 
> However, a query for the AAAA record for login.oscar.aol.com gives a 
> no-error no-answer result for login.glogin.messaging.aol.com!
> 
> The question in the question section of the result doesn't match the 
> question that was asked, and the client ignores it as bogus.
> 
> There's no CNAME record in the response to indicate to the client that 
> login.oscar.aol.com is actually an alias for 
> login.glogin.messaging.aol.com: the client asks for X and gets an answer 
> for Y, with no indication why an answer for Y is relevant.
> 
> >[chesh7:~] cheshire% dig -t aaaa login.oscar.aol.com
> >
> >; <<>> DiG 9.2.2 <<>> -t aaaa login.oscar.aol.com
> >;; global options:  printcmd
> >;; Got answer:
> >;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61168
> >;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
> >
> >;; QUESTION SECTION:
> >;login.glogin.messaging.aol.com.        IN      AAAA
> >
> >;; Query time: 82 msec
> >;; SERVER: 17.128.100.10#53(17.128.100.10)
> >;; WHEN: Tue Dec 14 11:41:55 2004
> >;; MSG SIZE  rcvd: 48
> >
> >[chesh7:~] cheshire% 
> 
> Is this a bogus caching DNS server, or is this kind of response normal 
> and expected? Should the client handle this, or is the client right to 
> ignore it?

	The client should reject the second answer.  You should upgrade /
	replace the offending nameserver.  Probably a old BIND 8 with the
	following bug.

1650.   [bug]           NODATA responses from forwarders that followed
                        a CNAME were not handled correctly.


> Stuart Cheshire <cheshire@apple.com>
>  * Wizard Without Portfolio, Apple Computer, Inc.
>  * www.stuartcheshire.org
> 
> 
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--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews@isc.org

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