RFC2181
10.2. PTR records
Confusion about canonical names has lead to a belief that a PTR
record should have exactly one RR in its RRSet. This is incorrect,
the relevant section of RFC1034 (section 3.6.2) indicates that the
value of a PTR record should be a canonical name. That is, it should
not be an alias. There is no implication in that section that only
one PTR record is permitted for a name. No such restriction should
be inferred.
And it get's used....
--($:~)-- dig -x 212.25.28.4
; <<>> DiG 9.2.2 <<>> -x 212.25.28.4
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31751
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 3, ADDITIONAL: 5
;; QUESTION SECTION:
;4.28.25.212.in-addr.arpa. IN PTR
;; ANSWER SECTION:
4.28.25.212.in-addr.arpa. 86400 IN PTR lexx.zh.as8758.net.
4.28.25.212.in-addr.arpa. 86400 IN PTR dns.as8758.net.
;; AUTHORITY SECTION:
28.25.212.in-addr.arpa. 86400 IN NS dns.dolphins.ch.
28.25.212.in-addr.arpa. 86400 IN NS moya.glb.as8758.net.
28.25.212.in-addr.arpa. 86400 IN NS dns.as8758.net.
;; ADDITIONAL SECTION:
dns.as8758.net. 292722 IN A 212.25.28.4
dns.dolphins.ch. 33522 IN A 212.25.25.8
dns.dolphins.ch. 33522 IN AAAA 2001:8e0:0:3::abcd
moya.glb.as8758.net. 292722 IN A 212.25.28.35
moya.glb.as8758.net. 119890 IN AAAA 2001:8e0:80::35
;; Query time: 630 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Sun Nov 16 14:37:46 2003
;; MSG SIZE rcvd: 262
sometimes "lexx" comes first... sometimes "dns"....
On Sun, Nov 16, 2003 at 12:05:57 +0000, Dan Boresjo wrote:
Not to mention all the common platforms out there that assume one-to-one.
For example the gethostbyaddr socket library function in both UNIX and
Windows.
Who do you want to blame? Those that use the RFC or those who ignore it?
If the ordering of records is not reliable either, this means that a
gethostbyaddr result is non-deterministic (unless coded to fail) if you have
multiple PTR records. Ouch.
Well I'm not a coder, but I suppose this function should handle it like
getipbyname - if there are multiple results, return all of them at let the
caller
decide what to do...
regards
Philipp
- Dan
On Sunday 16 November 2003 4:21 am, Tim Gladding wrote:
On Sun, 16 Nov 2003, Philipp Morger wrote:
An IP can have multiple PTR records - there's nothing wrong with this.
However, this can confuse some already existing anti-spam measures that
rely (good or bad) on a one to one match.
Tim
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