Network Working Group W A Simpson
Internet Draft Daydreamer
expires in six months February 1995
ICMP Domain Name Messages
draft-simpson-icmp-domain-name-00.txt
Status of this Memo
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Abstract
This document specifies ICMP messages for learning the Fully
Qualified Domain Name of a target, without laborious maintainance and
searching of an "inverse" DNS tree.
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DRAFT ICMP Domain Name February 1995
1. Introduction
The Domain Name System (DNS) is described in [RFC-1034]. The IN-ADDR
domain of the DNS is specified [RFC-1035] to perform address to
domain name mapping, and to facilitate queries to locate all gateways
(routers) on a particular network in the Internet.
Neither function has been remarkably successful. The IN-ADDR domain
is not reliably populated.
As multiple routers were used at the boundaries and within networks,
the IN-ADDR mechanism was found to be inadequate. The location of
routers by hosts is now performed using "ICMP Router Discovery
Messages" [RFC-1256].
As network numbers migrated to "classless" routing and aggregation,
the IN-ADDR delegation granularity has fragmented, and requires
overlapping administration. This structure is not amenable to
cooperative secure updating.
As application servers have appeared which require the Domain Name
for user interaction and security logging, the IN-ADDR servers have
been inundated with queries. This produces long user visible pauses
at the initiation of sessions.
Instead, this document proposes that each computer be queried
directly for its Domain Name. This has the advantages that the
mapping is under the same administration as the address assignment,
and the queries are distributed in the same fashion as IP routing.
In effect, the routing is used to index the mapping database.
The datagram format and basic facilities are already defined for ICMP
[RFC-792].
Up-to-date values of the ICMP Type field are specified in the most
recent "Assigned Numbers" [RFC-1700]. This document concerns the
following values:
37 Domain Name Request
38 Domain Name Reply
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DRAFT ICMP Domain Name February 1995
1.1. Domain Name Request
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 37
Code 0
Checksum The ICMP Checksum.
Identifier If Code is zero, a value to aid in matching requests
and replies. For example, it might be used like a
port in TCP or UDP to identify a session. May be
zero.
Sequence Number If Code is zero, a value to aid in matching requests
and replies. For example, the number might be
incremented on each request sent. May be zero.
A separate Domain Name Request is used for each IP Destination
queried.
An ICMP Domain Name Request received with a broadcast or multicast
Destination MUST be silently discarded.
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1.2. Domain Name Reply
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Names ...
+-+-+-+-+-+-+-+-
Type 38
Code 0
Checksum The ICMP Checksum.
Identifier Copied from the request.
Sequence Number Copied from the request.
Names zero or more Fully Qualified Domain Names. The
length of this field is determined from the total
length of the datagram.
Each name is expressed as a sequence of labels.
Each label is represented as a one octet length
field, followed by that number of octets. Since
every domain name ends with the null label of the
root, a domain name is terminated by a length byte
of zero. The high order two bits of every length
octet must be zero, and the remaining six bits of
the length field limit the label to 63 octets or
less.
To simplify implementations, the total length of a
domain name (including label octets and label length
octets) is restricted to 255 octets or less.
The Source in a Reply MUST be the same as the Destination of the
corresponding Request message.
Every host and router MUST implement an ICMP Domain Name server
function that receives Domain Name Requests and sends corresponding
Domain Name Replies. A host SHOULD also implement an application-
layer interface for sending a Domain Name Request and receiving a
Domain Name Reply, for diagnostic purposes.
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DRAFT ICMP Domain Name February 1995
Security Considerations
A primary purpose of this specification is to provide a mechanism for
updating and learning address to domain name mapping which is more
secure than IN-ADDR mapping.
Although the routing infrastructure to the Destination does not
provide security in and of itself, it is as least as reliable as
delivery of correspondence for the other sessions with the same peer.
Although the peer might not be accurate in its reply, this mechanism
is amenable to establishment of Security Associations for
authentication and privacy.
References
[RFC-792]
[RFC-1034]
[RFC-1035]
[RFC-1256]
[RFC-1700]
Author's Address
Questions about this memo can also be directed to:
William Allen Simpson
Daydreamer
Computer Systems Consulting Services
1384 Fontaine
Madison Heights, Michigan 48071
Bill.Simpson@um.cc.umich.edu
bsimpson@MorningStar.com
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