Suddenly no reverse DNS = no mail [Archive]

View Full Version : Suddenly no reverse DNS = no mail

doug

02-06-2004, 20:56

Until last Friday, I could read (POP) mail from my non-NTL ISP. Suddenly I found that connections to my mailhost were being refused - inconvenient as this was the Bank Holiday weekend. I now have discovered that the reason is that the originating address (spc1-with2-5-0-cust2.manc.broadband.ntl.com (213.106.179.2)) fails a reverse DNS lookup and the mail server refuses to connect to such a dubious origin.

The requirement to provide a reverse DNS lookup is in the RFCs:

http://www.cse.ohio-state.edu/cgi-bin/rfc/rfc1123.html#sec-6.1

The key phrase being:

"Every host MUST implement a resolver for the Domain Name System
(DNS), and it MUST implement a mechanism using this DNS resolver to
convert host names to IP addresses and vice-versa"

Who do I complain to? What happened on Friday? - I speculate that a new pool of addresses were released.

Paul

03-06-2004, 00:13

doug

03-06-2004, 13:24

:confused:

The IP that you mention does have a reverse dns lookup address - the one which you just listed (spc1-with2-5-0-cust2.manc.broadband.ntl.com) so I am baffled as to what you are saying ???

(btw, RFC's are not "law". Many IP addresses do not have any reverse lookup).

RFCs are not mandatory, but they do define the protocols by which the Internet functions. Non-compliance is just bad manners.

PEM is saying there is a hostname and equivalent host IP address; that is not the same as having a publically available reverse DNS.

Thus this address is verified:

nslookup -silent spr1-oldh4-5-0-cust189.manc.broadband.ntl.com
Server: 130.88.192.9
Address: 130.88.192.9#53

Non-authoritative answer:
Name: spr1-oldh4-5-0-cust189.manc.broadband.ntl.com
Address: 80.5.5.189

whereas this isn't:

nslookup -silent spc1-with2-5-0-cust2.manc.broadband.ntl.com
Server: 130.88.192.9
Address: 130.88.192.9#53

** server can't find spc1-with2-5-0-cust2.manc.broadband.ntl.com: NXDOMAIN

My guess is that NTL have forgotten to add the reverse entries for
all/part of one of their number ranges (they are in separate files
with the software we use).

Again I ask, to whom do I report this?

Paul

03-06-2004, 15:06

My guess is that NTL have forgotten to add the reverse entries for
all/part of one of their number ranges (they are in separate files
with the software we use).

Again I ask, to whom do I report this?

Who ? I don't know yet - I would imagine you could try e-mailing the cable support team - but who ever you report it to I think you need to lookup what "reverse dns" is.

Hostname > IP is a standard dns lookup
IP > Hostname is a reverse dns lookup

In the case of "spc1-with2-5-0-cust2.manc.broadband.ntl.com" it is the standard dns lookup that is missing (no A record).

HEADER:
opcode = QUERY, id = 12143, rcode = NAME_ERR
header flags: reply, want recursion, recursion avail.
questions = 1, answers = 0, auth. records = 0, additional = 0
QUESTIONS:
spc1-with2-5-0-cust2.manc.broadband.ntl.com., type = A, class = 1
*** complete ***

The reverse dns lookup (on 213.106.179.2, via in-addr.arpa) seems to work fine.

HEADER:
opcode = QUERY, id = 12181, rcode = NOERROR
header flags: reply, want recursion, recursion avail.
questions = 1, answers = 1, auth. records = 0, additional = 0
QUESTIONS:
2.179.106.213.in-addr.arpa., type = PTR, class = 1
ANSWERS:
-> 2.179.106.213.in-addr.arpa.
type = PTR, class = 1, ttl = 10800, dlen = 45
host = spc1-with2-5-0-cust2.manc.broadband.ntl.com.
*** complete ***

LenaJoel12

10-05-2011, 17:10

Who ? I don't know yet - I would imagine you could try e-mailing the cable support team - but who ever you report it to I think you need to lookup what "reverse dns" is.

I faced a similar issue in the past as yours and i had this question who should i report it to, and then found the best one helped me to resolve it was the cable support team, they should have engineering team for supporting all issues of same sort.

nodrogd

13-05-2011, 23:54

Oh God! Yet another zombie thread has woken up. !!!

Paul

14-05-2011, 00:33

7 Year bump :eek:

Why do I think, failed sig spammer.

Sirius

14-05-2011, 09:08

7 Year bump :eek:

Why do I think, failed sig spammer.

7 years :LOL: