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Versions: 00 01 02 03                                                   
Network Working Group                  Yakov Rekhter, Cisco Systems
Internet Draft                     Ralph Droms, Bucknell University
Expiration Date: August 1996                          February 1996

                            FQDN DHCP Option

1. Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
   munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
   ftp.isi.edu (US West Coast).

2. Abstract

   DHCP [DHCP] can be used to automate the process of configuring TCP/IP
   host computers.  However, some of the DHCP options carry IP addresses
   rather than Fully Qualified Domain Names (FQDN). Use of IP addresses
   constrains the DHCP client to use the addresses that were in use at
   the time the client received its configuration information; these
   addresses may change over time, (e.g., a server may be assigned a new
   IP address), so that the IP addresses used by the client may become

   An alternative to passing IP addresses is to pass FQDNs instead of
   (numeric) IP addresses.  Doing this allows to defer binding between a
   particular network entity (e.g., a server) and its IP address until
   run time.  As stated in [Carpenter:95], "Deferring the binding avoids
   the risk of changed mapping between IP addresses and specific network
   entities (due to changing addressing information).  Moreover,
   reliance on FQDNs (rather than IP addresses) also localizes to the
   DNS the changes needed to deal with changing addressing information
   due to renumbering."

Yakov Rekhter, Ralph Droms                                      [Page 1]

Internet Draft       draft-ietf-dhc-fqdn-opt-00.txt         January 1996

   This document defines a new DHCP option that allows the use of FQDNs
   instead of IP addresses in DHCP options.

3. Definitions

   The following defines the format of the FQDN option.

    | Code     |  Length  |
    |Subcode   |Sublength |             FQDN


    |Subcode   |Sublength |             FQDN

   The option consists of a Code and Length fields followed by a
   variable number of <subcode, sublength, FQDN> triples.

   The code, length, subcode, and sublength fields are all one octet
   long.  The FQDN field is of variable length.

   The code value for this option is TBD.

   The length field specifies the total length (in octets) of all the
   triples carried in the option.

   For each subcode carried in the FQDN option, the IP address in the
   option represented by the subcode is replace by a FQDN.

   The sublength field shall be set to the length (in octets) of the
   FQDN carried in the option.  The FQDN field carries the FQDN itself.

   More that one triple with a given subcode may appear within a single
   FQDN option.  Options that can carry a list of IP addresses should be
   coded as multiple subcodes in the FQDN option, to differentiate among
   the variable-length FQDNs.

   This option only allows the use of FQDNs for options that have been

Yakov Rekhter, Ralph Droms                                      [Page 2]

Internet Draft       draft-ietf-dhc-fqdn-opt-00.txt         January 1996

   elsewhere defined to carry IP addresses.

4. Example

   The following illustrates how the FQDN option could be used to carry
   FQDNs for 2 LPR Servers with FQDNs lpr1.xxx.org and lpr2.yy.org, and
   one Network Information Server with FQDN nis.zzzz.org.

    |xx |41 |
    |41 |12 | n | i | s | . | z | z | z | z | . | o | r | g |
    | 9 |12 | l | p | r | 1 | . | x | x | x | . | o | r | g |
    | 9 |11 | l | p | r | 2 | . | y | y | . | o | r | g |

5. Security Considerations

   Security issues are not discussed in this document.

6. References

   [Carpenter:95] Carpenter, B., Rekhter, Y., "Renumbering considered
   unavoidable", Internet Draft

   [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC1541,
   October 1993

Yakov Rekhter, Ralph Droms                                      [Page 3]

Internet Draft       draft-ietf-dhc-fqdn-opt-00.txt         January 1996

7. Acknowledgements

   To be supplied.

8. Author Information

   Yakov Rekhter
   cisco Systems, Inc.
   170 Tasman Dr.
   San Jose, CA 95134
   Phone: (914) 528-0090
   email: yakov@cisco.com

   Ralph Droms
   Computer Science Department
   323 Dana Engineering
   Bucknell University
   Lewisburg, PA 17837
   Phone: (717) 524-1145
   email: droms@bucknell.edu

Yakov Rekhter, Ralph Droms                                      [Page 4]