AT&T refuses to provide PTR records?

Jack Bates jbates at
Wed Oct 18 14:11:45 UTC 2006

Mark Foster wrote:
> Surely if you have _a_ matching forward and reverse DNS pair, that'd get 
> you started?
The problem in our case is that this wasn't an email issue. Any service 
(http/ftp/nntp/etc) which performed rDNS lookups prior to handling the 
connection would end up timing out the connection due to the fact that AT&T had 
setup a CNAME which pointed to a nameserver that no longer existed (from when 
the IP was owned by someone else). The actual complaint was failure to ftp files 
from the location due to the ftp server doing rDNS. AT&T refused to remove the 
old CNAME which was defunct. We didn't need matching anything. NXDOMAIN would 
have even been acceptable. However, forwarding the request to non-existent 
nameservers is not.

> The issue was where there was no matching A/PTR set, this would increase 
> the likelyhood of a spam host or something... right?

The issue was that when revoking an IP from a customer, AT&T did not remove the 
rDNS configuration for that IP. Had they done so, their own servers would have 
reported back that there wasn't any rDNS (NXDOMAIN) which would have been 
perfectly acceptable.

Jack Bates

More information about the NANOG mailing list