Network Working Group Yakov Rekhter, Cisco Systems
INTERNET DRAFT Ralph Droms, Bucknell University
Obsoletes: draft-ietf-dhc-fqdn-opt-00.txt April 1996
Expires October 1996
An option for FQDNs in DHCP options
<draft-ietf-dhc-fqdn-opt-01.txt>
Status of this Memo
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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
invalid.
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."
Rekhter, Droms [Page 1]
DRAFT An option for FQDNs in DHCP options April 1996
This document defines a new DHCP option that allows the use of FQDNs
instead of IP addresses in DHCP options.
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
elsewhere defined to carry IP addresses.
Rekhter, Droms [Page 2]
DRAFT An option for FQDNs in DHCP options April 1996
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 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+
Security Considerations
Security issues are not discussed in this document.
References
[Carpenter:95] Carpenter, B., Rekhter, Y., "Renumbering considered
unavoidable", Internet Draft
[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC1541,
October 1993
Acknowledgements
To be supplied.
Rekhter, Droms [Page 3]
DRAFT An option for FQDNs in DHCP options April 1996
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
Rekhter, Droms [Page 4]