MIPSHOP WG G. Bajko
Internet Draft Nokia
Intended Status: Proposed Standard October 17, 2008
Expires: April 16, 2009
Locating IEEE 802.21 Mobility Servers using DNS
draft-ietf-mipshop-mos-dns-discovery-04
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Abstract
This document defines application service tags that allow service
location without relying on rigid domain naming conventions, and DNS
procedures for discovering servers which provide IEEE 802.21
[IEEE802.21] defined Mobility Services. Such Mobility Services are
used to assist a Mobile Node (MN) supporting IEEE 802.21
[IEEE802.21], in handover preparation (network discovery) and
handover decision (network selection). The services addressed by
this document are the Media Independent Handover Services defined in
[IEEE802.21].
Conventions used in this document
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 RFC-2119.
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Terminology and abbreviations used in this document
Mobility Services: comprises of a set of different services provided
by the network to mobile nodes to facilitate handover preparation
and handover decision, as described in [IEEE802.21].
Mobility Server: a network node providing IEEE 802.21 Mobility
Services.
MIH: Media Independent Handover, as defined in [IEEE802.21].
MIH Service: IS, ES or CS type of service, as defined in
[IEEE802.21].
Application service: is a generic term for some type of
application, independent of the protocol that may be used to offer
it. Each application service will be associated with an IANA-
registered tag.
Application protocol: is used to implement the application service.
These are also associated with IANA-registered tags.
Table of Content
1. Introduction....................................................2
2. Discovering a Mobility Server...................................3
2.1 Selecting a Mobility Service..............................3
2.2 Selecting the transport protocol..........................4
2.3 Determining the IP address and port.......................5
3. IANA Considerations.............................................6
4. Security Considerations.........................................6
5. Normative References............................................6
6. Informative References..........................................7
7. Author's Address................................................7
1. Introduction
IEEE 802.21 [IEEE802.21] defines three distinct service types to
facilitate link layer handovers across heterogeneous technologies:
a) Information Services (IS)
IS provides a unified framework to the higher layer entities
across the heterogeneous network environment to facilitate
discovery and selection of multiple types of networks existing
within a geographical area, with the objective to help the
higher layer mobility protocols to acquire a global view of the
heterogeneous networks and perform seamless handover across
these networks.
b) Event Services (ES)
Events may indicate changes in state and transmission behavior
of the physical, data link and logical link layers, or predict
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state changes of these layers. The Event Service may also be
used to indicate management actions or command status on the
part of the network or some management entity.
c) Command Services (CS)
The command service enables higher layers to control the
physical, data link, and logical link layers. The higher layers
may control the reconfiguration or selection of an appropriate
link through a set of handover commands.
In IEEE terminology these services are called Media Independent
Handover (MIH) services.
While these services may be co-located, the different pattern and
type of information they provide does not necessitate the co-
location.
"Service Management" service messages, i.e., MIH registration, MIH
capability discovery and MIH event subscription messages, are
considered as ES and CS when transporting MIH messages over L3
transport.
An MN may make use of any of these MIH service types separately or
any combination of them.
It is anticipated that a Mobility Server will not necessarily host
all three of these MIH Services together, thus there is a need to
discover the MIH Service types separately.
This document defines a number of application service tags that
allow service location without relying on rigid domain naming
conventions.
2. Discovering a Mobility Server
The procedures defined here assume that the MN knows the domain name
of the network where it wants to locate a Mobility Server. The
domain name of the network can either be pre-configured, discovered
using DHCP or learned from a previous Information Service (IS) query
[IEEE802.21] as described in [ID.ietf-mipshop-mstp-solution].
The procedures defined here result in an IP address, port and
transport protocol where the MN can contact the Mobility Server
which hosts the service the MN is looking for.
2.1 Selecting a Mobility Service
The MN should know the characteristics of the Mobility Services
defined in [IEEE802.21] and based on that it should be able to
select the service it wants to use to facilitate its handover. The
services it can choose from are:
- Information Service (IS)
- Information Service over a secure connection (ISs)
- Event Service (ES)
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- Event Service over a secure connection (ESs)
- Command Service (CS)
- Command Service over a secure connection (CSs)
The service identifiers for the services are "IS","ISs", "ES",
"ESs", "CS" and "CSs" respectively.
The server supporting any of the above services MUST support at
least UDP and TCP as transport, as described in [ID.ietf-mipshop-
mstp-solution]. SCTP and other transport protocols MAY also be
supported.
2.2 Selecting the transport protocol
After the desired service has been chosen, the client selects the
transport protocol it prefers to use. Note, that transport selection
may impact the handover performance.
The services relevant for the task of transport protocol selection
are those with NAPTR service fields with values "ID+M2X", where ID
is the service identifier defined in the previous section and X is a
letter that corresponds to a transport protocol supported by the
domain. This specification defines M2U for UDP, M2T for TCP and M2S
for SCTP. This document also establishes an IANA registry for
NAPTR service name to transport protocol mappings.
These NAPTR [RFC3403] records provide a mapping from a domain to the
SRV [RFC2782] record for contacting a server with the specific
transport protocol in the NAPTR services field. The resource record
will contain an empty regular expression and a replacement value,
which indicates the domain name where the SRV record for that
particular transport protocol can be found. If the server supports
multiple transport protocols, there will be multiple NAPTR records,
each with a different service value. As per [RFC3403], the client
discards any records whose services fields are not applicable.
The MN MUST discard any service fields that identify a resolution
service whose value is not "M2X", for values of X that indicate
transport protocols supported by the client. The NAPTR processing
as described in RFC 3403 will result in the discovery of the most
preferred transport protocol of the server that is supported by the
client, as well as an SRV record for the server.
As an example, consider a client that wishes to find IS service in
the example.com domain. The client performs a NAPTR query for that
domain, and the following NAPTR records are returned:
order pref flags service regexp replacement
IN NAPTR 50 50 "s" "IS+M2T" "" _IS._tcp.example.com
IN NAPTR 90 50 "s" "IS+M2U" "" _IS._udp.example.com
This indicates that the domain does have a server providing IS
services over TCP and UDP, in that order of preference. Since the
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client supports TCP and UDP, TCP will be used, targeted to a host
determined by an SRV lookup of _IS._tcp.example.com. That lookup
would return:
;; Priority Weight Port Target
IN SRV 0 1 XXXX server1.example.com
IN SRV 0 2 XXXX server2.example.com
If no NAPTR records are found, the client constructs SRV queries for
those transport protocols it supports, and does a query for each.
Queries are done using the service identifier "_IS" for the
Information Service, "_ES" for the Event Service and "_CS" for
Command Service. A particular transport is supported if the query is
successful. The client MAY use any transport protocol it desires
which is supported by the server.
Note, that the regexp field in the NAPTR example above is empty.
This document discourages the use of this field as its usage can be
complex and error prone; and the discovery of the MIH services do
not require the flexibility provided by this field over a static
target present in the TARGET field.
As another example, consider a client which wishes to find ES
service over a secure connection. The client performs a NAPTR query
for that domain, and the following NAPTR records are returned:
order pref flags service regexp replacement
IN NAPTR 50 50 "s" "ESs+M2T" "" _ESs._tcp.example.com
IN NAPTR 90 50 "s" "ESs+M2U" "" _ESs._udp.example.com
This indicates that the domain does have a server providing ES
services over a secure connection, in the above case TLSoverTCP and
DTLSoverUDP.
When a transport protocol is specified explicitly, the client will
perform an SRV query for that specific transport using the service
identifier of the Mobility Service.
2.3 Determining the IP address and port
Once the server providing the desired service and the transport
protocol has been determined, the next step is to determine the IP
address and port.
If TARGET is a numeric IP address, the MN uses that IP address and
the already chosen transport to contact the server providing the
desired service.
If the TARGET was not a numeric IP address, then the MN performs an
A and/or AAAA record lookup of the domain name, as appropriate. The
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result will be a list of IP addresses, each of which can be
contacted using the transport protocol determined previously.
If the result of the SRV query contains a port number, then the MN
SHOULD contact the server at that port number. If the SRV record did
not contain a port number then the MN SHOULD contact the server at
the default port number of that particular service. A default port
number for MIH services is requested from IANA in [ID.ietf-mipshop-
mstp-solution].
3. IANA considerations
The usage of NAPTR records described here requires well known values
for the service fields for each transport supported by Mobility
Services. The table of mappings from service field values to
transport protocols is to be maintained by IANA.
The registration in the RFC MUST include the following information:
Service Field: The service field being registered.
Protocol: The specific transport protocol associated with that
service field. This MUST include the name and acronym for the
protocol, along with reference to a document that describes the
transport protocol.
Name and Contact Information: The name, address, email address
and telephone number for the person performing the
registration.
The following values have been placed into the registry:
Service Fields Protocol
IS+M2T TCP
ISs+M2T TLSoverTCP (RFC 5246)
IS+M2U UDP
ISs+M2U DTLSoverUDP (RFC 4347)
IS+M2S SCTP
ISs+M2S TSLoverSCTP (RFC 3436)
ES+M2T TCP
ESs+M2T TLSoverTCP (RFC 5246)
ES+M2U UDP
ESs+M2U DTLSoverUDP (RFC 4347)
ES+M2S SCTP
ESs+M2S TLSoverSCTP (RFC 3436)
CS+M2T TCP
CSs+M2T TLSoverTCP (RFC 5246)
CS+M2U UDP
CSs+M2U DTLSoverUDP (RFC 4347)
CS+M2S SCTP
CSs+M2S TLSoverSCTP (RFC 3436)
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New Service Fields are to be added via Standards Action as defined
in [RFC5226].
New entries to the table that specify additional transport protocols
for the existing Service Fields may be registered by IANA on a First
Come First Served' basis [RFC5226].
4. Security considerations
A list of known threats to services using DNS is documented in
[RFC3833]. For most of those identified threats, the DNS Security
Extensions [RFC4033] does provide protection. It is therefore
recommended to consider the usage of DNSSEC [RFC4033] and the
aspects of DNSSEC Operational Practices [RFC4641] when deploying
IEEE 802.21 Mobility Services.
In deployments where DNSSEC usage is not feasible, measures should
be taken to protect against forged DNS responses and cache poisoning
as much as possible. Efforts in this direction are documented in
[ID.ietf-dnsext-forgery-resilience].
5. Normative References
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Three: The Domain Name System (DNS) Database", RFC 3403,
October 2002.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC 4033,
March 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
2008.
6. Informative References
[IEEE802.21] IEEE 802.21 Standard for Local and Metropolitan Area
Networks: Media Independent Handover Services
[RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
RFC 4641, September 2006.
[RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain
Name System (DNS)", RFC 3833, August 2004.
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[ID.ietf-mipshop-mstp-solution] Mobility Services Transport Protocol
Design, Melia et al, April 2008, work in progress
[ID.ietf-dnsext-forgery-resilience] Measures for making DNS more
resilient against forged answers, Hubert et al, August 2008,
work in progress
7. Author's Addresses
Gabor Bajko
gabor(dot)bajko(at)nokia(dot)com
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