Network Working Group TC. Schmidt
Internet-Draft HAW Hamburg
Intended status: BCP M. Waehlisch
Expires: December 15, 2009 link-lab & FU Berlin
B. Sarikaya
Huawei USA
S. Krishnan
Ericsson
June 13, 2009
A Minimal Deployment Option for Multicast Listeners in PMIPv6 Domains
draft-schmidt-multimob-pmipv6-mcast-deployment-00
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Abstract
This document describes deployment options for activating multicast
listener functions in Proxy Mobile IPv6 domains without modifying
mobility and multicast protocol standards. Similar to Home Agents in
Mobile IPv6, PMIPv6 Local Mobility Anchors serve as multicast
subscription anchor points, while Mobile Access Gateways provide MLD
proxy functions. In this scenario, Mobile Nodes remain agnostic of
multicast mobility operations.
Requirements Language
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 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Deployment Details . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Operations of the Mobile Node . . . . . . . . . . . . . . 6
4.2. Operations of the Mobile Access Gateway . . . . . . . . . 6
4.3. Operations of the Local Mobility Anchor . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
Proxy Mobile IPv6 (PMIPv6) [RFC5213] extends Mobile IPv6 [RFC3775] by
network-based management functions that enable IP mobility for a host
without requiring its participation in any mobility-related
signaling. Additional network entities, i.e., the Local Mobility
Anchor (LMA), and Mobile Access Gateways (MAGs), are responsible for
managing IP mobility on behalf of the mobile node (MN).
With these routing entities in place, the mobile node looses
transparent end-to-end connectivity to the static Internet, and in
the particular case of multicast communication, group membership
management as signaled by the Multicast Listener Discovery protocol
[RFC3810], [RFC2710] requires a dedicated treatment, see
[I-D.deng-multimob-pmip6-requirement].
Multicast routing functions need a careful placement within the
PMIPv6 domain to augment unicast transmission with group
communication services. [RFC5213] does not explicitly address
multicast communication, whereas bi-directional home tunneling, the
minimal multicast support arranged by MIPv6, cannot be applied in
network-based management scenarios: A mobility-unaware node will
experience no reason to initiate a tunnel with an entity of mobility
support.
This document describes deployment options for activating multicast
listener functions in Proxy Mobile IPv6 domains without modifying
mobility and multicast protocol standards. Similar to Home Agents in
Mobile IPv6, PMIPv6 Local Mobility Anchors serve as multicast
subscription anchor points, while Mobile Access Gateways provide MLD
proxy functions. Mobile Nodes in this scenario remain agnostic of
multicast mobility operations. Accrediting the problem space of
multicast mobility [I-D.irtf-mobopts-mmcastv6-ps], this document does
not address optimization potentials and efficiency improvements of
multicast routing in network-centered mobility, as such solutions
would require changes to the base specification of [RFC5213].
2. Terminology
This document uses the terminology as defined for the mobility
protocols [RFC3775] and [RFC5213], as well as the multicast edge
related protocols [RFC3810] and [RFC4605].
The reference scenario for multicast deployment in Proxy Mobile IPv6
domains is illustrated in Figure 1.
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+-------------+
| Content |
| Source |
+-------------+
|
*** *** *** ***
* ** ** ** *
* *
* Fixed Internet *
* *
* ** ** ** *
*** *** *** ***
/ \
+----+ +----+
|LMA1| |LMA2| MLD Querier
+----+ +----+
LMAA1 | | LMAA2
| |
\\ //\\
\\ // \\
\\ // \\ Unicast Tunnel
\\ // \\
\\ // \\
\\ // \\
Proxy-CoA1 || || Proxy-CoA2
+----+ +----+
|MAG1| |MAG2| MLD Proxy
+----+ +----+
| | |
MN-HNP1 | | MN-HNP2 | MN-HNP3
MN1 MN2 MN3
Figure 1: Reference Network for Multicast Deployment in PMIPv6
3. Overview
An MN in a PMIPv6 domain will decide on multicast group membership
management completely independent of its current mobility conditions.
It will submit MLD Report and Done messages following application
desires, thereby using its link-local source address and multicast
destinations according to [RFC3810], or [RFC2710]. These link-local
signaling messages will arrive at the currently active MAG via one of
its downstream local (wireless) links. A multicast unaware MAG would
simply discard these MLD messages.
To facilitate multicast in a PMIPv6 domain, an MLD proxy function
[RFC4605] needs to be deployed on the MAG that selects the tunnel
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interface corresponding to the MN's LMA for its upstream interface
(cf., section 6 of [RFC5213]). Thereby each LMA upstream interface
defines an MLD proxy domain at the MAG, containing all downstream
links to MNs that share this LMA. MLD signaling of the MN will be
consequently forwarded up the tunnel interface to its corresponding
LMA.
Serving as the designated multicast router or an additional MLD
proxy, the LMA will transpose any MLD messages of the MN into the
multicast routing infrastructure. Correspondingly, the LMA will
implement appropriate multicast forwarding states at its tunnel
interface. Traffic arriving for groups under subscription will
arrive at the LMA, which it will forward according to all its group/
source states. In addition, the LMA will naturally act as an MLD
querier, seeing its downstream tunnel interfaces as multicast enabled
links.
At the MAG, MLD queries and multicast data will arrive on the
(tunnel) interface that is assigned to a group of access links as
identified by its Binding Update List (cf., section 6 of [RFC5213]).
As specified for MLD proxies, the MAG will forward multicast traffic
and related signaling down the appropriate access links to the MNs.
In proceeding this way, all multicast-related signaling and the
corresponding traffic will transparently flow from the LMA to the MN
on an LMA-specific shared tree.
In case of a mobility handover, the (IP mobility unaware) MN will
refrain from submitting unsolicited MLD reports. Instead, the LMA is
required to maintain group memberships in the following way. On the
reception of a Proxy Binding Update (PBU) from the new MAG and
successful Re-Binding, the LMA re-establishes a route to the MN's
home network prefix over the tunnel interface corresponding to the
new MAG (cf., section 5.3 of [RFC5213]).
After Re-Binding, the LMA SHOULD issue a general MLD query on the new
tunnel link to refresh forwarding requirements. Queries can be
omitted, if multicast forwarding states previously established at the
tunnel interface towards the new MAG form a superset of those present
at the old tunnel interface. The LMA SHOULD likewise perform a
general MLD query after receiving a Binding De-Registration at a
tunnel interface that is to be maintained. The LMA MAY reduce the
need for queries when it applies explicit tracking in combination
with [RFC3810].
These multicast deployment considerations likewise apply for mobile
nodes that operate with its IPv4 stack enabled in a PMIPv6 domain.
PMIPv6 can provide an IPv4 home address mobility support
[I-D.ietf-netlmm-pmip6-ipv4-support]. Such mobile node will use
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IGMPv3 [RFC3376] signaling for multicast, which is handled by an IGMP
proxy function at the MAG in an analogous way.
Following these deployment steps, multicast management transparently
interoperates with PMIPv6. It is worth noting that multicast streams
can possibly be distributed on redundant path, leading to duplicate
traffic arriving from different LMAs at one MAG, and causing multiple
data transmissions from a MAG over one wireless domain to different
MNs.
4. Deployment Details
Multicast activation in a PMIPv6 domain requires to deploy general
multicast functions at PMIPv6 routers and to define its interaction
with the PMIPv6 protocol in the following way:
4.1. Operations of the Mobile Node
A Mobile Node willing to manage multicast traffic will join, maintain
and leave groups as if located in the fixed Internet. No specific
mobility actions nor implementations are required at the MN.
4.2. Operations of the Mobile Access Gateway
A Mobility Access Gateway is required to assist in MLD signaling and
data forwarding between the MNs which it serves, and the
corresponding LMAs associated to each MN. It therefore needs to
implement an instance of the MLD proxy function [RFC4605] for each
upstream tunnel interface that has been established with an LMA. The
MAG decides on the mapping of downstream links to a proxy instance
(and hence an upstream link to an LMA) based on the regular Binding
Update List as maintained by PMIPv6 standard operations (cf., section
6.1 of [RFC5213]).
On the reception of MLD reports from an MN, the MAG MUST identify the
corresponding proxy instance from the incoming interface and perform
regular MLD proxy operations: it will insert/update/remove a
multicast forwarding state on the incoming interface and forward the
report to its upstream tunnel. Conversely on the reception of MLD
queries, the MAG proxy instance will transfer the queries to its
appropriate downstream interfaces. Multicast traffic arriving on an
upstream interface at the MAG will be forwarded according to the
group/source-specific forwarding states as acquired for each
downstream interface within the MLD proxy instance.
In case of a mobility handover, the MAG will continue to manage
upstream tunnels and downstream interfaces as foreseen in the PMIPv6
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specification. However, it MUST assure consistency of its up- and
downstream interfaces that change under mobility with MLD proxy
instances and its multicast forwarding states.
In proceeding this way, the MAG is entitled to aggregate multicast
subscriptions for each of its MLD proxy instances. However, this
deployment approach does not prevent multiple identical streams
arriving from different LMA upstream interfaces. Furthermore, a per
group forwarding into the wireless domain is restricted to the link
model in use.
4.3. Operations of the Local Mobility Anchor
For any MN, the Local Mobility Anchor acts as the persistent Home
Agent and at the same time as the default multicast querier. It
implements the function of the designated multicast router or a
further MLD proxy. According to MLD reports received from MNs (via
MAGs), it establishes/maintains/removes group/source-specific
multicast forwarding states at its downstream tunnel interfaces
established with MAGs, and at the same time procures for aggregated
multicast membership maintenance at its upstream interface. Based on
the multicast-transparent operations of the MAGs, the LMA experiences
its tunnel interfaces as multicast enabled downstream links serving
zero to many listening nodes. Multicast traffic arriving at the LMA
is transparently forwarded according to its multicast forwarding
states. The LMA MAY choose to apply explicit node tracking in
combination with MLDv2 [RFC3810].
On the occurrence of a mobility handover, the LMA will receive
Binding Lifetime De-Registrations and Binding Lifetime Extensions
that will cause a re-mapping of home network prefixes to Proxy-CoAs
in its Binding Cache. Correspondingly, the multicast forwarding
states require updating, as well. In the absence of explicit
tracking, the LMA MUST proceed as follows:
o Issue a general multicast query on a tunnel interface that is to
be maintained even though a De-Registration was received. Update
the multicast forwarding states according to the query outcome.
o Issue a general multicast query on a tunnel interface at which a
Lifetime Extension was received from a new Proxy-CoA, if the
multicast forwarding states at this interface do not form a
superset of the states established at the interface corresponding
to the previous Proxy-CoA.
For multicast membership queries, two cases need distinction:
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1. LMA multicast membership maintenance is unaffected by the
handover-related absence of the MN: In this case, the LMA
actively maintains states and continues to transmit multicast
packets to the down-tunnel towards the MN. The PMIPv6 protocol
will transfer the tunnel endpoints and access link binding states
between previous and new MAG, such that the MN can simply
continue to receive its group traffic under subscription.
Service interruptions are bound to the handover discontinuities
experienced for PMIPv6 unicast transmission.
2. A MN may be unable to answer LMA multicast membership queries due
to handover procedures. Such instance is equivalent to a general
query loss. To prevent erroneous query timeouts at the LMA, MLD
parameters SHOULD be carefully adjusted to the mobility regime.
In particular, MLD timers and the Robustness Variable (see
section 9 of [RFC3810]) MUST be chosen to be compliant with the
temporal handover operations of the PMIPv6 domain.
In proceeding this way, each LMA will provide transparent multicast
support for the group of MNs it serves. It will perform traffic
aggregation at the MN-group level and will assure that multicast data
streams are uniquely forwarded per individual LMA-to-MAG tunnel.
5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
This draft does neither introduce additional messages nor novel
protocol operations. Consequently, no new threats arrive from
procedures described in this document in excess to [RFC3810] and
[RFC5213] security concerns.
7. Acknowledgements
This memo is the outcome of extensive previous discussions and a
follow-up of several initial drafts on the subject. The authors
would like to thank Gorry Fairhurst for advice and reviews of the
document.
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8. References
8.1. Normative References
[I-D.ietf-netlmm-pmip6-ipv4-support]
Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", draft-ietf-netlmm-pmip6-ipv4-support-12
(work in progress), April 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
8.2. Informative References
[I-D.deng-multimob-pmip6-requirement]
Deng, H., Schmidt, T., Seite, P., and P. Yang, "Multicast
Support Requirements for Proxy Mobile IPv6",
draft-deng-multimob-pmip6-requirement-01 (work in
progress), October 2008.
[I-D.irtf-mobopts-mmcastv6-ps]
Fairhurst, G., Schmidt, T., and M. Waehlisch, "Multicast
Mobility in MIPv6: Problem Statement and Brief Survey",
draft-irtf-mobopts-mmcastv6-ps-07 (work in progress),
April 2009.
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Authors' Addresses
Thomas C. Schmidt
HAW Hamburg
Berliner Tor 7
Hamburg 20099
Germany
Email: schmidt@informatik.haw-hamburg.de
URI: http://inet.cpt.haw-hamburg.de/members/schmidt
Matthias Waehlisch
link-lab & FU Berlin
Hoenower Str. 35
Berlin 10318
Germany
Email: mw@link-lab.net
Behcet Sarikaya
Huawei USA
1700 Alma Dr. Suite 500
Plano, TX 75075
USA
Email: sarikaya@ieee.org
Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Email: suresh.krishnan@ericsson.com
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