Internet Engineering Task Force C. Perkins
INTERNET DRAFT IBM
14 March 1997
DHCP Options for Service Location Protocol
draft-ietf-dhc-slp-01.txt
Status of This Memo
This document is a submission to the Dynamic Host Configuration
Working Group of the Internet Engineering Task Force (IETF). Comments
should be submitted to the dhcp@bucknell.edu mailing list.
Distribution of this memo is unlimited.
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Abstract
The Dynamic Host Configuration Protocol provides a framework for
passing configuration information to hosts on a TCP/IP network.
Entities using the Service Location Protocol need to find out the
address of Directory Agents in order to transact messages. In
certain other instances they may need to discover the correct scope
to be used in conjunction with the service attributes and URLS which
are exchanged using the Service Location Protocol.
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1. Introduction
The Dynamic Host Configuration Protocol [2] provides a framework
for passing configuration information to hosts on a TCP/IP network.
Entities using the Service Location Protocol [3] need to find out
the address of Directory Agents in order to transact messages. In
certain other instances they may need to discover the correct scope
to be used in conjunction with the service attributes and URLs [1]
which are exchanged using the Service Location Protocol.
The scope MAY be denoted in any standardized character set. Values
for character encoding can be found in IANA's database
http://www.isi.edu/in-notes/iana/assignments/character-sets
and have the values referred by the MIBEnum value.
Note that each option listed below may be included multiple times in
the same DHCPOFFER or DHCPREQUEST. If so, then the options SHOULD be
included in order of decreasing preference.
2. Directory Agent Option
This option requests or specifies a Directory Agent (DA), along with
zero or more scopes supported by that DA.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length |D|S| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (if present) Directory Agent address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Char Encoding | scope ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code 78
Length variable
D If the 'D' bit is set, the Directory Agent address is
present.
S If the 'S' bit is set, the scope is present, encoded in
the indicated character set.
Char Encoding
The standardized encoding for the characters making up
the string denoting the scope.
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scope A string denoting the scope.
Note that more than one Directory Agent option may be present in a
DHCP message. Each such option may have the same or different scope.
The client may request any Directory Agent with a particular scope,
by including the Directory Agent option in a DHCP Request message
with no Directory Agent address included (the 'D' bit set to zero),
and the string denoting the scope. The length of the scope string is
only indicated implicitly by the overall length of the option.
3. Service Scope Option
This option indicates a scope that should be used by a Service Agent
(SA) [3], when responding to Service Request messages as specified by
the Service Location Protocol.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Char Encoding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| scope ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code 79
Length variable
Char Encoding
The standardized encoding for the characters making up
the string denoting the scope.
scope A string denoting the scope.
Note that more than one Service Scope option may be present in a DHCP
message. The length of the scope string is only indicated implicitly
by the overall length of the option.
4. Security Considerations
If a malicious host is able to insert fraudulent information in
DHCPOFFER packets sent to a prospective client of the Service
Location Protocol, then the client will be unable to obtain service,
and vulnerable to disclosing information to unauthorized service
agents. Likewise, a service agent would find that it might rely on
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fraudulent or otherwise malicious directory agents to advertise its
services. Many opportunities for denial of service exist.
This difficulty is inherited from the much larger and more serious
problem, viz. securing or authenticating any information whatsoever
from a DHCP server (or client!) is not possible in common DHCP
deployments.
5. Acknowledgements
Thanks to Erik Guttman for his helpful suggestions in the creation of
this draft.
References
[1] T. Berners-Lee, L. Masinter, and M. McCahill. Uniform Resource
Locators (URL). RFC 1738, December 1994.
[2] Ralph Droms. Dynamic Host Configuration Protocol. RFC 1541,
October 1993.
[3] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service
Location Protocol, November 1996. draft-ietf-svrloc-protocol-15.txt
(work in progress).
Author's Address
Questions about this memo can be directed to:
Charles E. Perkins
Sun Microsystems
2550 Garcia Avenue
Mountain View, CA 94043
Phone: +1 415 336 7153
Fax: +1 415 336 0670
EMail: charliep@acm.org
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