Internet Engineering Task Force Erik Guttman
INTERNET DRAFT Sun Microsystems
18 September 2000 Expires in six months
Service Location Protocol Modifications for IPv6
draft-ietf-svrloc-ipv6-10.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026 [1].
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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Abstract
The Service Location Protocol provides a scalable framework for the
discovery and selection of network services. Using this protocol,
computers using IP based networks no longer need so much static
configuration of network services for network based applications.
This is especially important as computers become more portable, and
users less tolerant of or less able to fulfill the demands of network
administration.
The Service Location Protocol, Version 2 is well defined for use over
IPv4 networks [3]: This document defines its use over IPv6 networks.
Since this protocol relies on UDP and TCP, the changes to support its
use over IPv6 are minor.
This document does not describe how to use SLPv1 [2] over IPv6
networks. There is at the time of this publication no implementation
or deployment of SLPv1 over IPv6. It is RECOMMENDED that SLPv2 be
used in general, and specifically on networks which support IPv6.
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Table of Contents
1. Protocol Changes . . . . . . . . . . . . . . . . . . . . 2
2. Eliminating support for broadcast SLP requests . . . . . 2
3. Address Specification for IPv6 Addresses in URLs . . . . 3
4. SLP multicast behavior over IPv6 . . . . . . . . . . . . 3
4.1. SLPv2 Multicast Group-IDs for IPv6 . . . . . . . . . . 3
4.2. SLPv2 Scoping Rules for IPv6 . . . . . . . . . . . . . 4
4.2.1 Joining SLPv2 Multicast Groups . . . . . . . . . . . . 5
4.2.2 Sending SLPv2 Multicast Messages . . . . . . . . . . . 5
4.2.3 Rules for Message Processing . . . . . . . . . . . . . 6
4.2.4 SLPv2 Agents with multiple interfaces . . . . . . . . 6
4.2.4.1 General Rules . . . . . . . . . . . . . . . . . . . . 7
4.2.4.2 Multihomed UA . . . . . . . . . . . . . . . . . . . . 7
4.2.4.3 Multihomed SA . . . . . . . . . . . . . . . . . . . . 8
4.2.4.4 Multihomed DA . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . 10
References . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Contact Information . . . . . . . . . . . . . . 11
Full Copyright Statement . . . . . . . . . . . . . . . . 11
1. Protocol Changes
The following are changes required to have the Service Location
Protocol work over IPv6. These changes include:
- Eliminating support for broadcast SLP requests
- Address Specification for IPv6 Addresses in URLs
- Use of IPv6 multicast addresses and IPv6 address scopes
- Restricted Propagation of Service Advertisements
2. Eliminating support for broadcast SLP requests
Service Location over IPv4 allows broadcasts to send Service Location
request messages. IPv6 makes use of link-local multicast in place of
broadcast. Broadcast-only configuration for SLP is not supported
under IPv6. If a User Agent wishes to make a request to discover
Directory Agents or make a request of multiple Service Agents, the
User Agent must multicast the request to the appropriate multicast
address.
This change modifies the requirements described in Section 6.1 (Use
of Ports, UDP and Multicast) of the Service Location Protocol [3].
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3. Address Specification for IPv6 Addresses in URLs
Whenever possible the DNS [4] name of the service should be used
rather than the numerical representation described in this section.
Service Location allows the use of the protocol without the benefit
of DNS. This is relevant when a group of systems is connected to
build a network without any previous configuration of servers to
support this network. When Service Location is used in this manner,
numerical addresses must be used to identify the location of
services.
The format of a "service:" URL is defined in [5]. This URL is an
``absolute URI'' as defined by [6].
A numerical IPv6 address, such as may be used in a "service:" URL, is
specified as in [7]. The textual representation defined for literal
IPv6 addresses in [8]:
ipv6-addr = "[" num-addr "]"
num-addr = ; Text represented IPv6 address syntax is as
; specified in RFC 2373 [8], Section 2.2,
Examples:
This is a site-local scoped address, as could be used in a
SLP DAAdvert message.
service:directory-agent://[FEC0::323:A3F9:25ff:fe91:109D]
This is a link-local scoped address, as could be used by a SA
to advertise its service on a IPv6 network with no routers or
DNS service.
service:printer:ipp://[FE80::a15A:93ff:fe5D:B098]:8080/path
4. SLP multicast and unicast behavior over IPv6
Section 4.1 describes how different multicast addresses are used for
transmitting and receiving SLPv2 messages over IPv6. Section 4.2
defines rules for the use of these addresses and covers scoped
address issues in general.
4.1 SLPv2 Multicast Group-IDs for IPv6
SLPv2 for IPv4 specifies only one multicast address, relative to an
Administratively Scoped Address range [10]. The reason only one
address was used is that there are only 256 relative assignments
available for this purpose [10]. IPv6, on the other hand, has scoped
addresses and enough space for a range of assignments.
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SLPv2 for IPv6 uses the following multicast group-id assignments:
FF0X:0:0:0:0:0:0:116 SVRLOC
FF0X:0:0:0:0:0:0:123 SVRLOC-DA
FF0X:0:0:0:0:0:1:1000 Service Location
-FF0X:0:0:0:0:0:1:13FF
These group-ids are combined with the scope prefix of the scope to
which the multicast message is to be sent.
The SVRLOC group-id is used for the following messages: Service Type
Request and Attribute Request messages.
The SVRLOC-DA group-id is used for multicast Service Requests for the
"service:directory-agent" service type. Also, DAs send unsolicited
DA Advert messages to the SVRLOC-DA multicast group-id.
All other multicast Service Request messages are sent to the
appropriate Service Location multicast group-id. SAs join the groups
which correspond to the Service Types of the services they advertise.
The group-id is determined using the algorithm provided in SLPv1. [2]
The Service Type string used in the SrvRqst is hashed to a value from
0-1023. This determines the offset into the FF0X::1:1000-13FF range.
The has algorithm is defined as follows:
An unsigned 32 bit value V is initialized to 0. Each byte of the
Service Type UTF-8 [11] encoded string value is considered
consecutively. The current value V is multiplied by 33, then the
value of the current string byte is added. Each byte in the Service
Type string is processed in this manner. The result is contained in
the low order 10 bits of V. For example, the following code
implements this algorithm:
unsigned long slp_hash(const char *pc, unsigned int len) {
unsigned long h = 0;
while (len-- != 0) {
h *= 33;
h += *pc++;
}
return (0x3FF & h); /* round to a range of 0-1023 */
}
4.2 SLPv2 Scoping Rules for IPv6
IPv6 provides different scopes for interface address configuration
and multicast addresses. A SLPv2 Agent might discover services that
it cannot use or not discover services which it could use unless
rules are given to prevent this.
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Say a SLPv2 UA, for example, could request a service using site-local
scope multicast and obtain a service: URL containing a link-local
literal address. If the service referred to were not on the same
link as the SLPv2 UA, the service could not be reached.
4.2.1 Joining SLPv2 Multicast Groups
A SLPv2 Agent MAY send a multicast message using any scope which it
is allowed to (see section 4.2.2). A SA and a DA MUST join all
groups to which a SLPv2 Agent may send a message. This ensures that
the SA or DA will be able to receive all multicast messages.
Specifically, a SLPv2 Agent MUST NOT join a multicast group which has
greater than scope for an interface than it is configured with for
use with unicast. For example, an interface which is only configured
with a link-local address joins groups in scopes with FF01 and FF02.
If the interface is configured with a site-local or global address,
the scope of all multicast groups joined can be no greater than scope
FF05. In this case, SLPv2 SAs and DAs MUST join multicast groups in
all the following scopes: FF01 - FF05.
A DA MUST join the SVRLOC-DA group to receive SrvRqst messages
requesting DAAdverts.
A SA MUST join the SVRLOC-DA group to receive DAAdvert messages, the
Service Location range of group-ids to receive SrvRqst messages. The
SA MAY join the SVRLOC group in order to receive SrvTypeRqst and
AttrRqst messages; these features are OPTIONAL for the SA to
implement.
A UA MAY join the SVRLOC-DA group at any or all of these scopes in
order to receive DAAdvert messages.
4.2.2 Sending SLPv2 Multicast Messages
A SLPv2 Agent MUST NOT send a multicast SLPv2 message using a
multicast scope greater than the scope of the SLPv2 message's source
address. The maximum scope for a SLPv2 multicast message is site-
local (FF05).
This prevents, for example, a site-local multicast message being sent
from a link-local source address.
A SLPv2 Agent MAY send a multicast SLPv2 message using any multicast
scope less than or equal to the SLPv2 message's source address.
A SLPv2 UA with an interface configured with a global address could
multicast a SrvRqst to any scope up to and including site-local, for
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instance.
4.2.3 Rules for Message Processing
SLPv2 SAs and DAs MUST determine which scope a service: URL address
is in. This may be possible by examining the URL if it contains a
numerical IPv6 address. If the URL contains a host name, the SA or
DA MUST resolve that name to a set of addresses.
A SLPv2 SA or DA MUST NOT respond to a SrvRqst with a service: URL
for a service with an address scope less than the request's source
address scope. The rules are given in Figure 1, below.
Request Source Address Scope
+------------+------------+---------+
| Link-Local | Site-Local | Global |
+-------------+------------+------------+---------+
Service | Link-Local | Respond | Drop | Drop |
Address +-------------+------------+------------+---------+
Scope | Site-Local | Respond | Respond | Drop |
+-------------+------------+------------+---------+
| Global | Respond | Respond | Respond |
+-------------+------------+------------+---------+
Figure 1: Out-of-Scope Rules
This prevents UAs from being able discover service: URLs for services
which cannot be accessed.
4.2.4 SLPv2 Agents with multiple interfaces
A scope zone, or a simply a zone, is a connected region of topology
of a given scope. For example, the set of links connected by routers
within a particular site, and the interfaces attached to those links,
comprise a single zone of site-local scope. To understand the
distinction between scopes and zones, observe that the topological
regions within two different sites are considered to be two DIFFERENT
zones, but of the SAME scope.
A host which has multiple interfaces by definition is attached to two
link-local zones. A host may also be attached to multiple zones of
other scopes.
A SLPv2 Agent MUST NOT propagate service advertisements from one zone
to another. Another way of saying this is a SLPv2 SA or DA MUST NOT
respond to a request from one zone with service information
associated with a service in a different scope.
The specific implication of these rules is discussed in the sections
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which follow.
4.2.4.1 General rules
Service Locations (in SrvReg, SrvRply, AttrRst, SAAdvert or DAAdvert
messages) whose locations are literal addresses MUST only be sent to
SLP agents located on the same zone.
For example, a service: URL containing a link-local address on link A
may be sent in a SLPv2 message on link A, to a link-local destination
address only.
Each interface of a multihomed device is potentially on a separate
link. It is often difficult to determine whether two interfaces are
connected to the same link. For that reason a prudent implementation
strategy is to not issue SLP messages containing link-local service
locations except on the interface where the service is known to
reside.
4.2.4.2 Multihomed UA
+----+ +----+ +----+
| SA |--------| UA |--------| DA |
+----+ Link 1 +----+ Link 2 +----+
(Zone 1) (Zone 2)
Figure 2: Multihomed UA
In Figure 2 the UA is multihomed. The UA can issue a service request
in Zone 1 and discover services on the SA or in Zone 2 and discover
services advertised by the DA. For example, if the request is issued
from a link-local source address, the SA will only reply with a
service available on link 1, the DA only with a service available on
link 2.
The UA MUST use active discovery to detect DAs before issuing
multicast requests, as per SLPv2 [3]. The UA MUST issue requests
using multicast scope FF02 to solicit DAAdvertisements. If the UA
has a site-local or global source address and does not discover a DA
with the request issued at link-local scope, it may reissue the
request with increasing scopes up to a maximum scope of FF05.
If the UA is unable to discover any DAs using multicast discovery, it
may issue site-local scope (FF05) or less multicast requests. Note
that the source address of the request must be of at least the scope
of the multicast, as described in section 4.2.2.)
If the UA wishes to discover all services, it must issue requests
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into both Zone 1 and 2.
4.2.4.3 Multihomed SA
+----+ +----+ +----+
| UA |--------| SA |--------| DA |
+----+ Link 1 +----+ Link 2 +----+
(Zone 1) (Zone 2)
Figure 3: Multihomed SA
In Figure 3, the SA is multihomed. The SA may receive a request from
the UA on Link 1 (Zone 1). The SA MUST NOT return service
information for services offered on a different zone as a request.
For example, the UA could discover services offered in Zone 1 not
Zone 2.
The SA may receive a DAAdvert on Link 2 (Zone 2). The SA MUST NOT
send a service registration to the DA for a service which is present
in Zone 1. The SA MUST register a service with the DA which is
present in Zone 2.
The SA MUST NOT include an address in a SAAdvert message which is
sent on a zone where the address is not valid. For example, the SA
MUST NOT send a SAAdvert onto link 2, if the SAADvert contains a
service: URL with a literal link-local scoped IPv6 address for Link
1.
The SA performs active DA discovery, as described in SLPv2 [3]. The
SA MUST issue requests using multicast scope FF02 to solicit
DAAdvertisements. If the SA has a site-local or global source
address, it MUST reissue the request with increasing scopes up to a
maximum scope of FF05. Active DA discovery must be attempted in both
Zone 1 and 2. This ensures that the SA will discover as many DAs in
its scope as possible.
4.2.4.4 Multihomed DA
+----+ +----+ +----+
| UA |--------| DA |--------| SA |
+----+ Link 1 +----+ Link 2 +----+
(Zone 1) (Zone 2)
Figure 4: Multihomed DA
In Figure 4, the DA is multihomed. The DA MUST keep track of which
interface registrations were made on. The DA MUST prevent a
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registration from the SA which contains a service information valid
in one zone from being discovered in another zone. For example,
services registered by the SA in Zone 2 would not be discoverable by
the UA in Zone 1.
Care must be taken when issuing DAAdverts. The DA must respond to
active DA discovery requests using the same scope as the request.
For instance, if the SA issues a SrvRqst message for service type
"service:directory" from a link-local source address, the DA MUST
respond with a link-local (link 2) source address.
The DA MUST multicast unsolicited DAAdverts on each interface using
link-local and site-local source addresses, unless it is only
configured with a link-local address. In that case, the DA MUST
issue DAAdverts with link-local scope only.
The DA URL MUST contain the address of the greatest scope the DA is
configured with in the zone. For instance, if the DA is configured
with a link-local, site-local and global address in Zone 2, it would
use the global address in the DA URL (as a literal IPv6 address).
5. IANA Considerations
The following IPv6 multicast group-id range assignment must be
registered with IANA.
FF0X::1:1000 - FF0X::1:13FF For SLPv2 service discovery.
This document defines how to use SLPv2 for link-local and site-local
scope service discovery. Future documents may define how SLPv2 may
be used with other multicast scopes.
The following multicast group-id range has already been registered
[9].
FF05::1:1000 - FF05::1:13FF For site-local service discovery.
6. Security Considerations
User Agents and Directory Agents MAY ignore all unauthenticated
Service Location messages when a valid IPSec association exists.
Service Agents and Directory Agents MUST be able to use the IP
Authentication and IP Encapsulating Security Payload for issuing and
processing Service Location messages whenever an appropriate IPSec
Security Association exists. [12]
SLP allows digital signatures to be produced to allow the
verification of the contents of messages. There is nothing in the
Modifications for IPv6 document which weakens or strengthens this
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technique.
Acknowledgments
Thanks to Dan Harrington, Jim Wood and Alain Durand, Thomas Narten,
Dave Thaler and Erik Nordmark for their reviews of this document.
John Veizades contributed to the original version of this document.
The hash function is modified from a code fragment attributed to
Chris Torek. Text on Scope Zones is taken from writing by Steve
Deering, Brian Haberman and Brian Zill.
References
[1] Bradner, S., "The Internet Standards Process -- Version 3",
RFC 2026, October 1996.
[2] Veizades, J., Guttman, E., Perkins, C., Kaplan, S., "Service
Location Protocol", RFC 2165, June 1997
[3] Guttman, E., Perkins, C., Veizades, J., Day, M., "Service
Location Protocol, Version 2", RFC 2608, June 1999.
[4] Mockapetris, P. V. "Domain names - concepts and facilities",
RFC 1034. November 1987.
Mockapetris, P. V. "Domain names - implementation and
specification", RFC 1035. November 1987.
[5] Guttman, E., Perkins, C., Kempf, J., "Service Templates and
URLs", RFC 2609, July 1999.
[6] Berners-Lee, T., Fielding, R., and Masinter, L. "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[7] Hinden, R., Carpenter, B., "Format for Literal IPv6 Addresses
in URL's", RFC 2732 , December, 1999.
[8] Hinden, R., Deering, S., "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[9] Hinden, R., Deering, S., "IPv6 Multicast Address Assignments",
RFC 2375, July 1997.
[10] Meyer, D., "Administratively Scoped IP Multicast", RFC 2365,
July 1998.
[11] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 2279, January 1998.
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[12] Kent, S., Atkinson, R. "Security Architecture for the Internet
Protocol", RFC 2401, November 1998.
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Author's Contact Information
Erik Guttman
Sun Microsystems
Eichhoelzelstr. 7
74915 Waibstadt Germany
Phone: +49 7263 911701
Email: Erik.Guttman@germany.sun.com
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