Internet Engineering Task Force C. Perkins
INTERNET DRAFT E. Guttman
Sun Microsystems
13 March
09 October 1998
DHCP Options for Service Location Protocol
draft-ietf-dhc-slp-03.txt
draft-ietf-dhc-slp-04.txt
Status of This Memo
This document is a submission by the Dynamic Host Configuration
Working Group of the Internet Engineering Task Force (IETF).
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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. Another
option provides an assignment of scope for configuration of SLP User
and Service Agents.
1. Introduction
The Dynamic Host Configuration Protocol [4] [3] provides a framework
for passing configuration information to hosts on a TCP/IP network.
Entities using the Service Location Protocol [7] Protocol, Version 2 [4] need to find out
obtain the address of Directory Agents in order to transact messages and obtain
the correct scope to be used in messages which are exchanged using
the Scope configuration. The
Service Location Protocol.
The scope MUST be encoded using the UTF8 character encoding [8] Protocol (SLP) provides a default configuration
for Scopes and have the values referred by the MIBEnum value. Note that
each character Directory Agents may require two or more octets of data for its
representation.
Note that each option listed below MAY be included multiple times in
the same DHCPOFFER discovered using multicast
or DHCPREQUEST. If so, then the options SHOULD broadcast. It is useful in a larger deployment to be
included able
to configure SLP Agents using DHCP, so as to centralize the
administration and to deploy SLP in order of decreasing preference. networks where multicast routing
is not available.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [2]. [1].
2. Typed Scope Lists
In Introduction
The DHCP options described below are used to configure Agents using
the Service Location Protocol, multiple service types can be hosted on
the same network node. However, DHCP typically configures computers
based on their IP address. It Version 2.
The SLP Directory Agent option is possible that different service
types on the same computer would be administered from different
scopes. Thus, options 78 and 79 have additional syntax used to allow this
more detailed style of service configuration.
In particular, configure User Agents and
Service Agents with the list location of scopes contained Directory Agents in the options is
syntactically separated into lists pertaining network.
These Directory Agents are assumed to each service type.
Grammatically, a typed-scope-list in a DHCPOFFER is structured as
follows:
typed-scope-list = one or more maybe-typed-scope-items,
separated by commas
maybe-typed-scope-item = typed-scope-item, or scope-list
typed-scope-item = '(' service-type '=' scope-list ')'
scope-list = one or more scope-items, comma-separated
A typed-scope-list in a DHCPREQUEST is structured as follows:
typed-scope-list = one or more maybe-typed-scope-items,
separated support all of the scopes
supplied by commas
maybe-typed-scope-item = typed-scope-item, or
maybe-empty-scope-list
typed-scope-item = '(' service-type '=' maybe-empty-scope-list ')'
maybe-empty-scope-list = zero or more scope-items, comma-separated
A service type has the format defined in [5], and a scope-item has SLP Scope Option.
If the format defined in [6] for "strval". Basically, a scope-item SLP Scope Option is absent, the scope string "default" is
used instead. If there is a character scope string that has alphanumeric characters not including
control characters or `(',`)',`,', \',`!',`<',`=',`>', or `~' Service
schemes are special cases of schemes as defined for general URLs [1].
The typed-scope-list MAY contain both untyped-scope-lists and
typed-scope-lists. Each scope-item in each untyped-scope-list
applies to every service type on the node.
As an example, the scope-list ``A,B,C'' denotes scopes A, B and C
for all service types configured using local
configuration on the client. In a DHCPREQUEST, this scope
string would indicate host that is used if no SLP Scope Option has
been sent. DHCP configuration takes precedence over the client wishes a directory agent which
supports ANY local
configuration of these three scopes. In a DHCPOFFER, the SLP scope
indicates that the directory agent supports ALL of the three scopes.
Suppose instead that service types "netman" and "proxystuff" are
residing on a DHCP client. Then, the typed-scope-list in a DHCPOFFER
could be,
(netman=mgmt),(proxystuff=math-dept,labs)
Assuming lists. SLP Agents (be they Directory
Agents, User Agents or Service Agents) which use the DHCP client SLP Directory
Agent Option MUST be configured with two service types "netman" and
"proxystuff" did not make any scope restriction, a corresponding
typed-scope-list in a DHCPREQUEST could be,
(netman=),(proxystuff=)
asking for scopes for those service types. scope.
3. SLP Directory Agent Option
This option requests or specifies a Directory Agent (DA), along with
zero the location of one or more scopes supported by that directory agent. SLP Directory
Agents.
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 = 78 | Length |D|F|M|S| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ a1 | a2 | DA Length |DA address (variable length) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Typed Scope List (variable length) a3 | a4 | a1 | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code 78
Length (variable)
The length of the option in bytes.
D If the 'D' bit is set, the Directory Agent field and the
DA Length fields are present.
F If the 'F' bit is set, the SLP Directory Agent is indicated
by including its variable length host name or Fully
Qualified Domain Name (FQDN) instead Option specifies a list of its IP address.
M If the 'M' bit addresses
for Directory Agents. Directory Agents MUST be listed in order of
preference, if there is set, an order of preference.
The address of the Directory Agent address is given in network byte order.
The length of the only one that may option MUST always be used, divisible by 4 and multicast methods for
discovering has a
minimum length of 4.
The Directory Agents listed in this option MUST NOT be used.
S If configured with
the 'S' bit is set, a non-empty subset of the scope is present.
rsv reserved; ignored upon reception; MUST be sent as zero
DA Length The length (in octets) of list that the Directory Agent field. receiving the
Directory Agent
The Fully Qualified Domain Name (FQDN), host name, or IP
address of Option is configured with. See the Directory Agent.
Typed Scope List
The characters denoting the scope (see Section reftsl).
In order to simplify administration of the configuration of Directory
Agents for notes below.
SLPv2 Service Location Protocol clients, Agents which are configured using the SLP Directory
Agent
can be indicated by presenting its FQDN or host name instead of its
IP address. This allows renumbering Option MUST send a SrvRqst to proceed more smoothly [3].
When the FQDN or host name is used, DAs in the server DHCPOFFER. This
SLPv2 SrvRqst sets the 'F' bit. The
host name can be distinguished from Scope List to the FQDN value configured by the presence of a '.'
character. In any case, SLP
Scope Option if one was sent or "DEFAULT" otherwise. The service
type for the DA length field request is set to be the length
of the Directory Agent field. When "service:directory-agent" and the 'F' bit predicate
is not set, omitted. The reply will include the DA
Length DA's attributes, scope list.
The SA MUST be 4.
Note that more than one Directory Agent option may be present in a
DHCP message. Each such option may have register all service with the same DA which it advertises
which are advertised in one or different scope.
The client may request any Directory Agent with a particular scope,
by including more of the Directory Agent option scopes in a DHCP Request message
with the DA's scope
list. The SA MUST register no Directory Agent address included (the 'D' bit set to zero),
and faster than the characters denoting "min-lifetime" and not
slower than the scope.
The length "max-lifetime" attributes of the Typed Scope List is only indicated implicitly DA. These attributes
are obtained in the DAAdvert solicited by the overall length of SA after it receives
the option. This string is NOT null
terminated.
The format of SLP Directory Agent Option DHCPOFFER.
SLPv2 User Agents which are configured using the Typed Scope List field is described in section 2. SLP Directory Agent
Option 78 MUST include one or more scopes if a DA address is
returned. Using option 78, it is not possible for different service
types on the same node send their requests to be configured with different directory
agents. In other words, all service types on the same node will be
configured with DAs listed, using the same directory agent. entire
list of scopes they are configured with.
4. SLP Service Scope Option
This option
The scope list is a comma delimited list which indicates one or more the scopes
that should be used by a Service SLP Agent (SA) [7], when responding is configured to Service Request messages as
specified by the Service Location Protocol. use.
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 = 79 | Length | Typed-Scope-List <Typed Scope List> String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code 79
The Length (variable) indicates the number of bytes which follow. Since the
Scope-List String is encoded using UTF8 characters, it may be the
cast that the Length is not the same as the number of characters in
the Scope-List String.
The minimum length is 0, and the maximum length is 256. This imposes
a limit on the size of the Scope-List String which can be delivered
which does not exist in SLP. DHCP administrators will therefore have
to be careful to not configure very long scope names or very long
lists of scopes for any Agents in their network.
The Typed Scope List includes a list of scopes for the SLP Agent.
The list may be a list of scopes, such as "north,south,east,west".
The list may also include items which are 'typed scopes.' These
items indicate that SAs MUST advertise particular service types in
a scope other than that given in the scope list. UAs MUST issue
requests for services of these types in the scopes listed, or some
subset of the scopes. DAs ignore typed scopes in the SLP Service
Scope Option.
For example, "default,(service:printer:lpr=Math Department)"
indicates that SAs advertise all services in scope default except
for lpr printers, which are advertised in the Math Department scope.
UAs will request all services using the "default" scope, except lpr
printers, which are advertised in the option "Math Department" scope. DAs
will simply be configured in bytes. the scope "default" since they ignore
the typed scope argument.
The grammar for the typed scope list is:
ts-list = ts-item / ts-item `,' ts-list
ts-item = scope-list / `(' srv-type `=' scope-list `)'
srv-type = ALPHA *srv-safe [ `.' 1*srv-safe ]
srv-safe = ALPHA / DIGIT / `+' / `-'
scope-list = scope-item / scope-item "," scope-list
scope-item = 1*safe-scope
safe-scope = ; Any character except rsvd-scope.
; Reserved characters must be escaped.
rsvd-scope = `(' / `)' / `,' / `\' / `!' / `<' / `=' / `>' / `~'
CTL / `;' / `*' / `+'
escaped = `$\backslash$' HEXDIGIT HEXDIGIT
This grammar follows ABNF rules [2]. Reserved characters used in
scope names must be escaped. Reserved characters denoting in <srv-type> names
are not allowed. Note that <srv-type> names may include a Naming
Authority extension.
4.1. Zero Length Scope-List String Configuration
A SLP Service Scope Option which indicates a Length of 0 configures
the scope.
The Typed-Scope-List SLP Agent to use "User Selectable Scopes".
If this is described done, the SLP Agent MUST NOT be configured using the SLP
Directory Agent Option.
Instead, the SLP Agent will discover scopes using Directory Agent
discovery (or Service Agent Discovery) as defined in Section 2. [4].
The DHCP client
(i.e., user agent or service agent) which receives this option SLP Agent will then use the indicated scope for in aggregation of all SLP requests and registrations.
The scopes it
discovers on the network to configure its own scope string must be UTF8 character encoded. This string list.
Note that this configuration is not
null terminated.
DHCP clients MAY use Option 79 tantamount to request scopes removing all
centralized control of the configuration hosts on the network. This
makes it possible for one every User Agent to see every service. This
may not be desirable as users may not be able to or more
particular service types. desire to decide
which services are appropriate for them.
5. 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, SLP Agent then the client SLP Agent
will be unable to obtain service, or may unwittingly be directed to
use the incorrect services.
Many opportunities for denial of service exist. A service agent
could find that it might rely on fraudulent or otherwise malicious
directory agents to advertise its services. DHCPOFFERs could prevent
the regular SLP framework from functioning by directing clients to
not use multicast, to use nonexistent directory agents and so on.
These difficulties are 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.
6. Acknowledgements
Thanks to Erik Guttman for his helpful suggestions in the creation
ane revision of this draft.
References
[1] T. Berners-Lee, L. Masinter, and M. McCahill. Uniform Resource
Locators (URL). RFC 1738, December 1994.
[2] S. Bradner. Key words Words for use Use in RFCs to Indicate Requirement
Levels. RFC 2119, March 1997.
[3] B. Carpenter
[2] D. Crocker and Y. Rekhter. Renumbering needs work. P. Overell. Augmented BNF for Syntax
Specifications: ABNF. RFC 1900,
February 1996.
[4] 2234, November 1997.
[3] R. Droms. Dynamic Host Configuration Protocol. RFC 2131, March
1997.
[5] E. Guttman, C. Perkins, and J. Kempf. Service Templates and
service: Schemes. draft-ietf-svrloc-service-scheme-05.txt,
November 1997. (work in progress).
[6]
[4] E. Guttman, C. Perkins, J. Veizades, and M. Day. Service
Location Protocol version 2. draft-ietf-svrloc-protocol-v2-04.txt,
March 1998. (work in progress).
draft-ietf-svrloc-protocol-v2-04.txt,
[7] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan. Service
Location Protocol. RFC 2165, July 1997.
[8] F. Yergeau. UTF-8, a transformation format of unicode and ISO
10646. RFC 2279, January 1998.
Author's Address
Questions about this memo can be directed to:
Charles E. Perkins Erik Guttman
Technology Development Group Technology Development Group
Mail Stop MPK15-214
Room 2682 Mail Stop UFRA02
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email: charles.perkins@Sun.COM
charles.perkins@Eng.sun.com
cperkins@Eng.sun.com Charles.Perkins@Sun.Com Erik.Guttman@Sun.Com
Web: http://www.svrloc.org/~charliep