Internet Engineering Task Force C. Perkins
INTERNET DRAFT IBM
27 August 1996
DHCP Options for Service Location Protocol
draft-ietf-dhc-slp-00.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
and naming authority to be used in conjunction with the service
attributes and URLS which are exchanged using the Service Location
Protocol.
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1. Directory Agent Extension
This extension specifies a Directory Agent (DA) [3], along with zero
or more Naming Authorities [2] known to that DA and zero or more
scopes supported by that DA.
The code for this extension is 78. Each Naming Authority and each
scope MUST be a null-terminated string of ASCII characters. The
lengths of the strings are only indicated implicitly by their null
termination and the overall length of the extension.
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| NA count | scope count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (if present) |
| Directory Agent address (16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NA list ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| scope list ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code 78
Length variable
D If the 'D' bit is set, the Directory Agent address is
present.
NA count
The number of Naming Authorities indicated by strings in
the NA list following.
scope count
The number of scopes indicated by strings in the scope
list following.
NA list
A list of strings denoting Naming Authorities.
scope list
A list of strings denoting scopes.
Note that more than one Directory Agent extension may be present in
a DHCP message. Each such extension may have the same or different
lists of Naming Authorities and scopes. The client may request a
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Directory Agent with a particular scope, and/or knowledgeable about
schemes defined by a particular Naming Authority, by including the
Directory Agent extension in a DHCP Request message with no Directory
Agent address included (the 'D' bit set to zero), and the appropriate
strings in the NA list and/or scope list.
2. Service Scope Extension
This extension 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.
Code Len
+-----+-----+-----+-----
| 79 | n | Scope ...
+-----+-----+-----+-----
Scope is a null-terminated ASCII string, of length 'n' including the
terminating null character.
3. Naming Authority Extension
This extension indicates a naming authority (which specifies the
syntax for schemes that may be used in URLs [1]) for use by entities
with the Service Location Protocol.
Code Len
+-----+-----+-----+-----+-----+-----
| 80 | n | Naming Authority ...
+-----+-----+-----+-----+-----+-----
Naming Authority is a null-terminated ASCII string, of length 'n'
including the terminating null character.
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
fraudulent or otherwise malicious directory agents to advertise its
services. Many opportunities for denial of service exist.
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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] Paul E. Hoffman and Ron Daniel, Jr. Generic URN Syntax.
draft-ietf-uri-urn-syntax-00.txt -- work in progress, April 1995.
[3] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service
Location Protocol. draft-ietf-svrloc-protocol-14.txt - work in
progress, June 1996.
Author's Address
Questions about this memo can be directed to:
Charles Perkins
Room J1-A25
T. J. Watson Research Center
IBM Corporation
30 Saw Mill River Rd.
Hawthorne, NY 10532
Work: +1 914 7847350
Fax: +1 914 7847007
E-mail: perk@watson.ibm.com
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