AT&T Managed Internet
Service (MIS)
DNS Hosting of Forward and Reverse Zones
NOTE:
Per the Managed Internet Service (MIS) Service Guide and per Good DNS Maintenance
Practice, a Policy position has been prepared on the hosting of Forward and Reverse zones, also known
as in- addr.arpa. zones. Per the MIS Guide, any forward domain with the “.name” extension is not
supported by the MIS DNS Offer. In most cases, DNS is used to provide the IP address of a given
forward domain name. However, there are instances where an IP address must be mapped to a domain
name. The process of translating from an IP address to a domain name is termed a “reverse look-up”
through the use of pointer records. There should be only one pointer per host or network device or
element. Find below more detailed information regarding AT&T’s Policy statement regarding the hosting
of Reverse zones which describes when and under what circumstances AT&T will provide reverse DNS or
look-up.
Policy Statement
Simply stated, the written policy is that AT&T will provide in-addr.arpa hosting if we are already
hosting the associated forward domain. This requires the use of reverse pointers (PTR) records, which
map the IP address to the host names in queries. Some applications such as Microsoft require a client
to have reverse pointers as a security measure to validate who the user is. Also, FTP applications will
require the use of reverse pointers as a security measure in order to ftp data and/or web pages.
The criteria that needs to be met for AT&T to provide reverse look-up services are listed below:
1) IP block must be assigned by AT&T (Please note that just having an IP block and no forward
domain is not sufficient).
2) If a customer owns their own IP block it must be delegated to our Name Servers.
3) If a customer has an IP block from another ISP it must be delegated to our Name Servers.
4) At least one forward domain must be hosted on our servers for all three of the conditions
listed above.
5) The one forward domain must not be a lame delegation* but must contain at least one DNS
record and not be a dead zone**.
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affiliated companies. All other trademarks are the property of their owners. This document provides important information about your service. It is subject to
change. It is not part of your Customer Agreement (including Service Guide) with AT&T, and if there is a conflict between this document and the Customer
Agreement, the terms of the Customer Agreement control.
Good DNS and Business Criteria
Although it is technically feasible to provide reverse look-up without hosting the forward domain, this
becomes problematic from both a practical and business standpoint. Customers will request changes to
their DNS records for their forward domain and then assume these changes will also be reflected for
their reverse pointers. If one ISP is handling the forward domain and another the reverse zone this
assumption breaks down since there is no mechanism in place for the different ISP’s to communicate
with each other. From a Good DNS standpoint AT&T is in keeping with the industry wide standard of
not doing “half” of the DNS. However, there are some ISP’s that will not provide Reverse DNS nor will
they provide it for IP blocks not under their jurisdiction, such as the 12 block IP addresses owned by
AT&T.
Find below a listing of known ISP’s that at this time will not provide Reverse DNS for one or more of
the reasons stated above:
UUNET, Network Solutions (a.k.a., NSI ), Yahoo, Verio, Interland and Bell Nexxia
Customer Options
For those situations where the customer is having their forward DNS hosted by one of the ISP’s listed,
the customer will have no other alternative but to move at least one of their forward domains to the
AT&T Service which will allow us to then host the pointer records for the IP address in question. If a
customer expresses a reluctance to move their DNS to AT&T because they are already hosting their web
or mail records with another ISP, this can be mitigated by the fact that our DNS Service can point their
web or mail records to any non-AT&T IP address they desire, so that their existing service with that ISP
will not be affected.
For those situations where the customer is dealing with an ISP that is not specifically listed above or
where the other ISP may give consideration to hosting the Reverse Pointer for an AT&T MIS block, the
customer can be provided with written instructions by the DNS Care Team to be provided to the
customer’s existing ISP, advising as to how to set up a reverse zone on their DNS Server for a partial
IP block. These instructions are also covered under the Special DNS Instructions that can be found
under the MIS Implementation Planner at the URL of http://planner.bus.att.com and at the URL of
https://mis-att.bus.att.com under the Policies link.
* A Lame Delegation occurs when a zone has been registered and has been pointed to WHOIS Root
Servers, but the zone may or may not exist on AT&T servers. In order to be eligible to have reverse
DNS provided by AT&T the zone must exist on AT&T servers and have records associated with the
zone.
** A Dead Zone is a zone which has no underlying DNS records and therefore cannot be resolved.
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