Internet DRAFT - draft-schmidt-multimob-fmipv6-pfmipv6-multicast
draft-schmidt-multimob-fmipv6-pfmipv6-multicast
MULTIMOB Group T C. Schmidt
Internet-Draft HAW Hamburg
Intended status: Standards Track M. Waehlisch
Expires: April 23, 2013 link-lab & FU Berlin
R. Koodli
Cisco Systems
G. Fairhurst
University of Aberdeen
October 20, 2012
Multicast Listener Extensions for MIPv6 and PMIPv6 Fast Handovers
draft-schmidt-multimob-fmipv6-pfmipv6-multicast-07
Abstract
Fast handover protocols for MIPv6 and PMIPv6 define mobility
management procedures that support unicast communication at reduced
handover latency. Fast handover base operations do not affect
multicast communication, and hence do not accelerate handover
management for native multicast listeners. Many multicast
applications like IPTV or conferencing, though, are comprised of
delay-sensitive real-time traffic and will benefit from fast handover
execution. This document specifies extension of the Mobile IPv6 Fast
Handovers (FMIPv6) and the Fast Handovers for Proxy Mobile IPv6
(PFMIPv6) protocols to include multicast traffic management in fast
handover operations. This multicast support is provided first at the
control plane by a management of rapid context transfer between
access routers, second at the data plane by an optional fast traffic
forwarding that MAY include buffering.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 23, 2013.
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Multicast Context Transfer between Access Routers . . . . 6
3.2. Protocol Operations Specific to FMIPv6 . . . . . . . . . . 8
3.3. Protocol Operations Specific to PFMIPv6 . . . . . . . . . 10
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Protocol Operations Specific to FMIPv6 . . . . . . . . . . 13
4.1.1. Operations of the Mobile Node . . . . . . . . . . . . 13
4.1.2. Operations of the Previous Access Router . . . . . . . 14
4.1.3. Operations of the New Access Router . . . . . . . . . 15
4.2. Protocol Operations Specific to PFMIPv6 . . . . . . . . . 15
4.2.1. Operations of the Mobile Node . . . . . . . . . . . . 15
4.2.2. Operations of the Previous MAG . . . . . . . . . . . . 15
4.2.3. Operations of the New MAG . . . . . . . . . . . . . . 16
4.2.4. IPv4 Support Considerations . . . . . . . . . . . . . 17
5. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. Multicast Indicator for Proxy Router Advertisement
(PrRtAdv) . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2. Extensions to Existing Mobility Header Messages . . . . . 18
5.3. New Multicast Mobility Option . . . . . . . . . . . . . . 18
5.4. New Multicast Acknowledgement Option . . . . . . . . . . . 20
5.5. Length Considerations: Number of Records and Addresses . . 22
5.6. MLD (IGMP) Compatibility Aspects . . . . . . . . . . . . . 22
6. Security Considerations . . . . . . . . . . . . . . . . . . . 22
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 24
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Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
Mobile IPv6 [RFC3775] defines a network layer mobility protocol
involving mobile nodes participation, while Proxy Mobile IPv6
[RFC5213] provides a mechanism without requiring mobility protocol
operations at a Mobile Node (MN). Both protocols introduce traffic
disruptions on handovers that may be intolerable in many application
scenarios. Mobile IPv6 Fast Handovers (FMIPv6) [RFC5568], and Fast
Handovers for Proxy Mobile IPv6 (PFMIPv6) [RFC5949] improve these
handover delays for unicast communication to the order of the maximum
delay needed for link switching and signaling between Access Routers
(ARs) or Mobile Access Gateways (MAGs) [FMIPv6-Analysis].
No dedicated treatment of seamless multicast data reception has been
proposed by any of the above protocols. MIPv6 only roughly defines
multicast for Mobile Nodes using a remote subscription approach or a
home subscription through bi-directional tunneling via the Home Agent
(HA). Multicast forwarding services have not been specified at all
in [RFC5213], but are subject to current specification [RFC6224]. It
is assumed throughout this document that mechanisms and protocol
operations are in place to transport multicast traffic to ARs. These
operations are referred to as 'JOIN/LEAVE' of an AR, while the
explicit techniques to manage multicast transmission are beyond the
scope of this document.
Mobile multicast protocols need to serve applications such as IPTV
with high-volume content streams to be distributed to potentially
large numbers of receivers, and therefore should preserve the
multicast nature of packet distribution and approximate optimal
routing [RFC5757]. It is undesirable to rely on home tunneling for
optimizing multicast. Unencapsulated, native multicast transmission
requires establishing forwarding state, which will not be transferred
between access routers by the unicast fast handover protocols. Thus
multicast traffic will not experience expedited handover performance,
but an MN - or its corresponding MAG in PMIPv6 - can perform remote
subscriptions in each visited network.
This document specifies extensions of FMIPv6 and PFMIPv6 for
including multicast traffic management in fast handover operations.
The solution common to both underlying protocols defines the per-
group transfer of multicast contexts between ARs or MAGs. The
protocol defines corresponding message extensions necessary for
carrying group context information independent of the particular
handover protocol. ARs or MAGs are then enabled to treat multicast
traffic according to fast unicast handovers and with similar
performance. No protocol changes are introduced that prevent a
multicast unaware node from performing fast handovers with multicast
aware ARs or MAGs.
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This specification is applicable when a mobile node has joined and
maintains one or several multicast group subscriptions prior to
undergoing a fast handover. It does not introduce any requirements
on the multicast routing protocols in use, nor are the ARs or MAGs
assumed to be multicast routers. It assumes network conditions,
though, that allow native multicast reception in both, the previous
and new access network. Methods to bridge regions without native
multicast connectivity are beyond the scope of this document.
2. Terminology
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].
The use of the term, "silently ignore" is not defined in RFC 2119.
However, the term is used in this document and can be similarly
construed.
This document uses the terminology of [RFC5568], [RFC5949],
[RFC3775], and [RFC5213]. In addition, the following terms are
introduced:
3. Protocol Overview
The reference scenario for multicast fast handover is illustrated in
Figure 1.
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*** *** *** ***
* ** ** ** *
* *
* Multicast Cloud *
* *
* ** ** ** *
*** *** *** ***
/ \
/ \
/ \
+........../..+ +..\..........+
. +-------+-+ .______. +-+-------+ .
. | PAR |()_______)| NAR | .
. | (PMAG) | . . | (NMAG) | .
. +----+----+ . . +----+----+ .
. | . . | .
. ___|___ . . ___|___ .
. / \ . . / \ .
. ( P-AN ) . . ( N-AN ) .
. \_______/ . . \_______/ .
. | . . | .
. +----+ . . +----+ .
. | MN | ----------> | MN | .
. +----+ . . +----+ .
+.............+ +.............+
Figure 1: Reference Network for Fast Handover
3.1. Multicast Context Transfer between Access Routers
In a fast handover scenario (cf. Figure 1), ARs/MAGs establish a
mutual binding and provide the capability to exchange context
information concerning the MN. This context transfer will be
triggered by detecting MN's forthcoming move to a new AR and assist
the MN to immediately resume communication on the new subnet link
using its previous IP address. In contrast to unicast, multicast
stream reception does not primarily depend on address and binding
cache management, but requires distribution trees to adapt so that
traffic follows the movement of the MN. This process may be
significantly slower than fast handover management [RFC5757].
Multicast listeners at handover may take the twofold advantage of
including the multicast groups under subscription in context
transfer. First, the NAR can proactively join the desired groups as
soon as it gains knowledge of them. Second, multicast streams MAY be
included in traffic forwarding via the tunnel established from PAR to
NAR.
There are two modes of operation in FMIPv6 and in PFMIPv6. The
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predictive mode allows for AR-binding and context transfer prior to
an MN handover, while in the reactive mode, these steps are executed
after detection that the MN has re-attached to NAR. Details of the
signaling schemes differ between FMIPv6 and PFMIPv6 and are outlined
in Section 3.2 and Section 3.3.
In a predictive fast handover, the access router (i.e., PAR (PMAG) in
Figure 1) learns about the impending movement of the MN and
simultaneously about the multicast group context as specified in
Section 3.2 and Section 3.3. Thereafter, PAR will initiate an AR-
binding and context transfer by transmitting a HI message to NAR
(NMAG). HI is extended by multicast group states carried in mobility
header options as defined in Section 5.3. On reception of the HI
message, NAR returns a multicast acknowledgement in its HACK answer
that indicates its ability to support each requested group (see
Section 5.4). NAR (NMAG) expresses its willingness to receive
multicast traffic from forwarding by PAR using standard MLD
signaling. There are several reasons to waive forwarding, e.g., the
group could already be under native subscription or capacity
constraints can hinder decapsulation of additional streams at the
NAR. On the previous network side, forwarding of multicast traffic
can be in conflict with capacity or policy constraints of PAR.
For the groups requested, PAR MAY add the tunnel interface to its
multicast forwarding database, so that multicast streams can be
forwarded in parallel to unicast traffic. NAR, taking the role of an
MLD proxy [RFC4605] with upstream router PAR, will submit an MLD
report on this upstream tunnel interface to request the desired
groups, but will terminate multicast forwarding [RFC3810] from PAR,
as soon as group traffic natively arrives. In addition, NAR
immediately joins all groups that are not already under subscription
using its native multicast upstream interface and loopback as
downstream. It starts to downstream multicast forwarding after the
MN has arrived.
In a reactive fast handover, PAR will learn about the movement of the
MN, after the latter has re-associated with the new access network.
Also from the new link, it will be informed about the multicast
context of the MN. As group membership information are present at
the new access network prior to context transfer, MLD join signaling
can proceed in parallel to HI/HACK exchange. Following the context
transfer, multicast data can be forwarded to the new access network
using the PAR-NAR tunnel of the fast handover protocol. Depending on
the specific network topology though, multicast traffic for some
groups may natively arrive before it is forwarded from PAR.
In both modes of operation, it is the responsibility of the PAR
(PMAG) to properly react on the departure of the MN in the context of
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local group management. Depending on the multicast state management,
link type and MLD parameters deployed (cf., [RFC5757]), it is
requested to take appropriate actions to adjust multicast service to
requirements of the remaining nodes.
In this way, the MN will be able to participate in multicast group
communication with a handover performance comparable to that for
unicast, while network resource consumption is minimized.
3.2. Protocol Operations Specific to FMIPv6
ARs that provide multicast support in FMIPv6 will advertise this
general service by setting an indicator bit (M-bit) in its PrRtAdv
message as defined in Section 5.1. Additional details about the
multicast service support, e.g., flavors and groups, will be
exchanged within HI/HACK dialogs later at handovers.
An MN operating FMIPv6 will actively initiate the handover management
by submitting a fast binding update (FBU). The MN, which is aware of
the multicast groups it wishes to maintain, will attach mobility
options containing its group states (see Section 5.3) to the FBU, and
thereby inform ARs about its multicast context. ARs will use these
multicast context options for inter-AR context transfer.
In predictive mode, FBU is issued on the previous link and received
by PAR as displayed in Figure 2. PAR will extract the multicast
context options and append them to its HI message. From the HACK
message, PAR will redistribute the multicast acknowledgement by
adding the corresponding mobility options to its FBACK message. From
receiving FBACK, the MN will learn about a per group multicast
support in the new access network. If some groups or a multicast
flavour are not supported, it MAY decide on taking actions to
compensate the missing service. Note that the proactive multicast
context transfer may proceed successfully, even if the MN misses the
FBACK message on the previous link.
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MN PAR NAR
| | |
|------RtSolPr------->| |
|<-----PrRtAdv--------| |
| | |
| | |
|---------FBU-------->|----------HI--------->|
| (Multicast MobOpt) | (Multicast MobOpt) |
| | |
| |<--------HAck---------|
| | (Multicast AckOpt) |
| | Join to
| | Multicast
| | Groups
| | |
| <-----FBack---|--FBack------> |
| (Multicast AckOpt) | (Multicast AckOpt) |
| | |
disconnect optional |
| packet ================>|
| forwarding |
| | |
connect | |
| | |
|------------UNA --------------------------->|
|<=================================== deliver packets
| |
Figure 2: Predictive Multicast Handover for FMIPv6
The call flow for reactive mode is visualized in Figure 3. After
attaching to the new access link and performing an unsolicited
neighbor advertisement (UNA), the MN issues an FBU which NAR forwards
to PAR without processing. At this time, the MN is able to re-join
all desired multicast groups without relying on AR assistance.
Nevertheless, multicast context options are exchanged in the HI/HACK
dialog to facilitate intermediate forwarding of requested streams.
Note that group traffic possibly already arrives from a MN's
subscription at the time NAR receives the HI message. Such streams
may be transparently excluded from forwarding by setting an
appropriate multicast acknowledge option. In any case, NAR MUST
ensure that not more than one stream of the same group is forwarded
to the MN.
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MN PAR NAR
| | |
|------RtSolPr------->| |
|<-----PrRtAdv--------| |
| | |
disconnect | |
| | |
| | |
connect | |
|-------UNA-----------|--------------------->|
|-------FBU-----------|---------------------)|
| (Multicast MobOpt) |<-------FBU----------)|
| | |
Join to | |
Multicast | |
Groups | |
| |----------HI--------->|
| | (Multicast MobOpt) |
| |<-------HAck----------|
| | (Multicast AckOpt) |
| | |
| |(HI/HAck if necessary)|
| | |
| FBack, optional |
| packet forwarding ==========>|
| | |
|<=================================== deliver packets
| |
Figure 3: Reactive Multicast Handover for FMIPv6
3.3. Protocol Operations Specific to PFMIPv6
In a proxy mobile IPv6 environment, the MN remains agnostic of
network layer changes, and fast handover procedures are operated by
the access routers or MAGs. The handover initiation, or the re-
association respectively are managed by the access networks.
Consequently, access routers need to be aware of multicast membership
state at the mobile node. There are two ways to obtain record of
MN's multicast membership. First, MAGs MAY perform an explicit
tracking (cf., [RFC4605], [RFC6224]) or extract membership status
from forwarding states at node-specific point-to-point links.
Second, routers can perform general queries at handovers. Both
methods are equally applicable. However, a router that does not
operate explicit tracking MUST query its downstream links subsequent
to handovers. In either case, the PAR will become knowledgeable
about multicast group subscriptions of the MN.
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In predictive mode, the PMAG (PAR) will learn about the upcoming
movement of the mobile node. Without explicit tracking, it will
immediately submit a general MLD query and learn about the multicast
groups under subscription. As displayed in Figure 4, it will
initiate binding and context transfer with the NMAG (NAR) by issuing
a HI message that is augmented by multicast contexts in the mobility
options defined in Section 5.3. NAR will extract multicast context
information and act as described in Section 3.1.
PMAG NMAG
MN P-AN N-AN (PAR) (NAR)
| | | | |
| Report | | | |
|---(MN ID,-->| | | |
| New AP ID) | | | |
| | HO Indication | |
| |--(MN ID, New AP ID)-->| |
| | | | |
| | | Optional: |
| | | MLD Query |
| | | | |
| | | |------HI---->|
| | | |(Multicast MobOpt)
| | | | |
| | | |<---HAck-----|
| | | |(Multicast AckOpt)
| | | | |
| | | | Join to
| | | | Multicast
| | | | Groups
| | | | |
| | | |HI/HAck(optional)
| | | |<- - - - - ->|
| | | | |
| | | optional packet |
| | | forwarding =======>|
disconnect | | | |
| | | | |
connect | | | |
| MN-AN connection | AN-MAG connection |
|<----establishment----->|<----establishment------->|
| | | (substitute for UNA) |
| | | | |
|<========================================== deliver packets
| | | | |
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Figure 4: Predictive Multicast Handover for PFMIPv6
In reactive mode, the NMAG (NAR) will learn about MN's attachment to
the N-AN and establish connectivity by means of PMIPv6 protocol
operations. However, it will have no knowledge about multicast state
at the MN. Triggered by a MN attachment, the NMAG will send a
general MLD query and thereafter join the requested groups. In the
case of a reactive handover, the binding is initiated by NMAG, and
the HI/HACK message semantic is inverted (see [RFC5949]). For
multicast context transfer, the NMAG attaches to its HI message those
group identifiers it requests to be forwarded from PMAG. Using the
identical syntax in its multicast mobility option headers as defined
in Section 5.4, PMAG acknowledges those requested groups in its HACK
answer that it is willing to forward . The corresponding call flow
is displayed in Figure 5.
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PMAG NMAG
MN P-AN N-AN (PAR) (NAR)
| | | | |
disconnect | | | |
| | | | |
connect | | | |
| | | | |
| MN-AN connection | AN-MAG connection |
|<---establishment---->|<----establishment------->|
| | |(substitute for UNA & FBU)|
| | | | |
| | | | MLD Query
| | | | |
| | | | Join to
| | | | Multicast
| | | | Groups
| | | |
| | | |<------HI----|
| | | |(Multicast MobOpt)
| | | | |
| | | |---HAck----->|
| | | |(Multicast AckOpt)
| | | | |
| | | | |
| | | |HI/HAck(optional)
| | | |<- - - - - ->|
| | | | |
| | | optional packet |
| | | forwarding =======>|
| | | | |
|<======================================== deliver packets
| | | | |
Figure 5: Reactive Multicast Handover for PFMIPv6
4. Protocol Details
4.1. Protocol Operations Specific to FMIPv6
4.1.1. Operations of the Mobile Node
A Mobile Node willing to manage multicast traffic within fast
handover operations will inform about its MLD listener state records
within handover signaling.
When sensing a handover in predictive mode, an MN will build a
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Multicast Mobility Option as described in Section 5.3 that contains
the MLD (IGMP) multicast listener state and append it to the Fast
Binding Update (FBU) prior to signaling with PAR. It will receive
the Multicast Acknowledgement Option(s) as part of Fast Binding
Acknowledge (FBack) (see Section 5.4) and learn about unsupported or
prohibited groups at the NAR. The MN MAY take appropriate actions
like home tunneling to bridge missing multicast services in the new
access network. No multicast-specific operation is required by the
MN when re-attaching in the new network besides standard FMIPv6
signaling.
In reactive mode, the MN appends an identical Multicast Mobility
Option to FBU sent after its reconnect. In response, it will learn
about the Multicast Acknowledgement Option(s) from FBACK and expect
corresponding multicast data. Concurrently it joins all desired
multicast groups (channels) directly on its newly established access
link.
4.1.2. Operations of the Previous Access Router
A PAR will advertise its multicast support by setting the M-bit in
PrRtAdv.
In predictive mode, a PAR will receive the multicast listener state
of a MN prior to handover from the Multicast Mobility Option appended
to the FBU. It will forward these records to NAR within HI messages
and will expect Multicast Acknowledgement Option(s) in HACK, which
itself is returned to the MN as an appendix to FBACK. In performing
multicast context exchange, the AR is instructed to include the PAR-
to-NAR tunnel obtained from unicast handover management in its
multicast downstream interfaces and await MLD listener reports from
NAR. In response to receiving multicast subscriptions, PAR will
normally forward group data acting as a normal multicast router or
proxy. However, NAR MAY refuse to forward some or all of the
multicast streams.
In reactive mode, PAR will receive the FBU augmented by the Multicast
Mobility Option from the new network, but will continue with an
identical multicast record exchange in the HI/HACk dialog. As in the
predictive case, it will configure the PAR-to-NAR tunnel for
multicast downstream and forward data according to MLD reports
obtained from NAR, if capable of forwarding.
In both modes, PAR will interpret the first of the two events, the
departure of the MN or the reception of the Multicast Acknowledgement
Option(s) as a multicast LEAVE message of the MN and react according
to the signaling scheme deployed in the access network (i.e., MLD
querying, explicit tracking).
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4.1.3. Operations of the New Access Router
NAR will advertise its multicast support by setting the M-bit in
PrRtAdv.
In predictive mode, a NAR will receive the multicast listener state
of an expected MN from the Multicast Mobility Option appended to the
HI message. It will extract the MLD/IGMP records from the message
and intersect the request subscription with its multicast service
offer. Further on it will adjoin the supported groups (channels) to
the MLD listener state using loopback as downstream interface. This
will lead to suitable regular subscriptions on its native multicast
upstream interface without additional forwarding. Concurrently, NAR
builds a Multicast Acknowledgement Option(s) (see Section 5.4)
listing those groups (channels) unsupported on the new access link
and returns them within HACK. As soon as the bidirectional tunnel
from PAR to NAR is operational, NAR joins the groups desired for
forwarding on the tunnel link.
In reactive mode, NAR will learn about the multicast listener state
of a new MN from the Multicast Mobility Option appended to HI at a
time, when the MN has already performed local subscriptions of the
multicast service. Thus NAR solely determines the intersection of
requested and supported groups (channels) and issues the join
requests for group forwarding on the PAR-NAR tunnel interface.
In both modes, NAR MUST send a LEAVE message to the tunnel
immediately after forwarding of a group (channel) becomes unneeded,
e.g., after native multicast traffic arrives or group membership of
the MN terminates.
4.2. Protocol Operations Specific to PFMIPv6
4.2.1. Operations of the Mobile Node
A Mobile Node willing to participate in multicast traffic will join,
maintain and leave groups as if located in the fixed Internet. It
will cooperate in handover indication as specified in [RFC5949] and
required by its access link-layer technology. No multicast-specific
mobility actions nor implementations are required at the MN in a
PMIPv6 domain.
4.2.2. Operations of the Previous MAG
A MAG receiving a handover indication for one of its MNs follows the
predictive fast handover mode as a PMAG. It MUST issue an MLD
General Query immediately on its corresponding link unless it
performs an explicit tracking on that link. After gaining knowledge
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of the multicast subscriptions of the MN, the PMAG builds a Multicast
Mobility Option as described in Section 5.3 that contains the MLD
(IGMP) multicast listener state. If not empty, this Mobility Option
is appended to the regular fast handover HI messages, or - in the
case of unicast HI message being submitted prior to multicast state
detection - sent in an additional HI message to the NMAG. PMAG then
waits for receiving the Multicast Acknowledgement Option(s) with HACK
(see Section 5.4) and the creation of the bidirectional tunnel with
NMAG. Thereafter PMAG will add the tunnel to its downstream
interfaces in the multicast forwarding database. For those groups
(channels) reported in the Multicast Acknowledgement Option(s), i.e.,
not supported in the new access network, PMAG normally takes
appropriate actions (e.g., forwarding, termination) in concordance
with the network policy. It SHOULD start forwarding traffic down the
tunnel interface for those groups it receives an MLD listener report
message from NMAG. However, it MAY deny forwarding service. After
the departure of the MN and on the reception of LEAVE messages for
groups/channels, PMAG MUST terminate forwarding of the specific
groups and update its multicast forwarding database. Correspondingly
it issues a group/channel LEAVE to its upstream link, if no more
listeners are present on its downstream links.
A MAG receiving a HI message with Multicast Mobility Option for a
currently attached node follows the reactive fast handover mode as a
PMAG. It will return Multicast Acknowledgement Option(s) (see
Section 5.4) within HACK listing those groups/channels unsupported at
NMAG. It will add the bidirectional tunnel with NMAG to its
downstream interfaces and will start forwarding multicast traffic for
those groups it receives an MLD listener report message from NMAG.
At the reception of LEAVE messages for groups (channels), PMAG MUST
terminate forwarding of the specific groups and update its multicast
forwarding database. According to its multicast forwarding states,
it MAY need to issue a group/channel LEAVE to its upstream link, if
no more listeners are present on its downstream links.
In both modes, PMAG will interpret the departure of the MN as a
multicast LEAVE message of the MN and react according to the
signaling scheme deployed in the access network (i.e., MLD querying,
explicit tracking).
4.2.3. Operations of the New MAG
A MAG receiving a HI message with Multicast Mobility Option for a
currently unattached node follows the predictive fast handover mode
as NMAG. It will decide on those multicast groups/channels it wants
forwarded from the PMAG and builds a Multicast Acknowledgement Option
(see Section 5.4) that enumerates only unwanted groups/channels.
This Mobility Option is appended to the regular fast handover HACK
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messages, or - in the case of unicast HACK message being submitted
prior to multicast state acknowledgement - sent in an additional HACK
message to the PMAG. Immediately thereafter, NMAG SHOULD update its
MLD listener state by the new groups/channels obtained from the
Multicast Mobility Option. Until the MN re-attaches, NMAG uses its
loopback interface for downstream and does not forward traffic to the
potential link of the MN. NMAG SHOULD issue JOIN messages for those
newly adopted groups to its regular multicast upstream interface. As
soon as the bidirectional tunnel with PMAG is established, NMAG
additionally joins those groups/channels on the tunnel interface that
it wants to receive by forwarding from PMAG. NMAG MUST send a LEAVE
message to the tunnel immediately after forwarding of a group/channel
becomes unneeded, e.g., after native multicast traffic arrives or
group membership of the MN terminates.
A MAG experiencing a connection request for a MN without prior
reception of a corresponding Multicast Mobility Option is operating
in the reactive fast handover mode as NMAG. Following the re-
attachment, it immediately issues an MLD General Query to learn about
multicast subscriptions of the newly arrived MN. Using standard
multicast operations, NMAG joins the missing groups (channels) on its
regular multicast upstream interface. Concurrently, it selects
groups (channels) for forwarding from PMAG and builds a Multicast
Mobility Option as described in Section 5.3 that contains the MLD
(IGMP) multicast listener state. If not empty, this Mobility Option
is appended to the regular fast handover HI messages with the F flag
set, or - in the case of unicast HI message being submitted prior to
multicast state detection - sent in an additional HI message to the
PMAG. Upon reception of the Multicast Acknowledgement Option and
upcoming of the bidirectional tunnel, NMAG additionally joins those
groups/channels on the tunnel interface that it wants to receive by
forwarding from PMAG. When multicast streams arrive, the NMAG
forwards data to the appropriate downlink(s). NMAG MUST send a LEAVE
message to the tunnel immediately after forwarding of a group/channel
becomes unneeded, e.g., after native multicast traffic arrives or
group membership of the MN terminates.
4.2.4. IPv4 Support Considerations
An MN in a PMIPv6 domain may use an IPv4 address transparently for
communication as specified in [RFC5844]. For this purpose, LMAs can
register IPv4-Proxy-CoAs in its Binding Caches and MAGs can provide
IPv4 support in access networks. Correspondingly, multicast
membership management will be performed by the MN using IGMP. For
multiprotocol multicast support on the network side, IGMPv3 router
functions are required at both MAGs (see Section 5.6 for
compatibility considerations with previous IGMP versions). Context
transfer between MAGs can transparently proceed in HI/HACK message
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exchanges by encapsulating IGMP multicast state records within
Multicast Mobility Options (see Section 5.3 and Section 5.4 for
details on message formats.
It is worth mentioning the scenarios of a dual-stack IPv4/IPv6 access
network, and the use of GRE tunneling as specified in[RFC5845].
Corresponding implications and operations are discussed in the PMIP
Multicast Base Deployment document, cf., [RFC6224].
5. Message Formats
5.1. Multicast Indicator for Proxy Router Advertisement (PrRtAdv)
An FMIPv6 AR will indicate its multicast support by activating the
M-bit in its Proxy Router Advertisements (PrRtAdv). The message
extension has the following format.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Subtype |M| Reserved | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 6: Multicast Indicator Bit for Proxy Router Advertisement
(PrRtAdv) Message
5.2. Extensions to Existing Mobility Header Messages
The fast handover protocols use a new IPv6 header type called
Mobility Header as defined in [RFC3775]. Mobility headers can carry
variable Mobility Options.
Multicast listener context of an MN is transferred in fast handover
operations from PAR/PMAG to NAR/NMAG within a new Multicast Mobility
Option, and acknowledged by a corresponding Acknowledgement Option.
Depending on the specific handover scenario and protocol in use, the
corresponding option is included within the mobility option list of
HI/HAck only (PFMIPv6), or of FBU/FBAck/HI/HAck (FMIPv6).
5.3. New Multicast Mobility Option
The Multicast Mobility Option contains the current listener state
record of the MN obtained from the MLD Report message, and has the
format displayed in Figure 7.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Option-Code | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ MLD (IGMP) Report Payload +
~ ~
~ ~
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Mobility Header Multicast Option
Type: TBD
Length: 8-bit unsigned integer. The size of this option in 8 octets
including the Type, Option-Code, and Length fields.
Option-Code:
1: IGMPv3 Payload Type
2: MLDv2 Payload Type
3: IGMPv3 Payload Type from IGMPv2 Compatibility Mode
4: MLDv2 Payload Type from MLDv1 Compatibility Mode
Reserved: MUST be set to zero by the sender and MUST be ignored by
the receiver.
MLD (IGMP) Report Payload: this field is composed of the MLD (IGMP)
Report message after stripping its ICMP header. Corresponding
message formats are defined for MLDv2 in [RFC3810], and for IGMPv3 in
[RFC3376].
Figure 8 shows the Report Payload for MLDv2, while the payload format
for IGMPv3 is defined corresponding to the IGMPv3 payload format (see
Section 5.2. of [RFC3810], or Section 4.2 of [RFC3376]) for the
definition of Multicast Address Records).
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |No of Mcast Address Records (M)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | . .
. Multicast Address Record [1] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Multicast Address Record [2] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
. . .
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Multicast Address Record [M] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: MLDv2 Report Payload
5.4. New Multicast Acknowledgement Option
The Multicast Acknowledgement Option reports the status of the
context transfer and contains the list of state records that could
not be successfully transferred to the next access network. It has
the format displayed in Figure 9.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Option-Code | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ MLD (IGMP) Unsupported Report Payload +
~ ~
~ ~
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Mobility Header Multicast Acknowledgement Option
Type: TBD
Length: 8-bit unsigned integer. The size of this option in 8 octets.
The length is 1 when the MLD (IGMP) Unsupported Report Payload field
contains no Mcast Address Record.
Option-Code: 0
Status:
1: Report Payload type unsupported
2: Requested group service unsupported
3: Requested group service administratively prohibited
Reserved: MUST be set to zero by the sender and MUST be ignored by
the receiver.
MLD (IGMP) Unsupported Report Payload: this field is syntactically
identical to the MLD (IGMP) Report Payload field described in
Section 5.3, but is only composed of those multicast address records
that are not supported or prohibited in the new access network. This
field MUST always contain the first header line (reserved field and
No of Mcast Address Records), but MUST NOT contain any Mcast Address
Records, if the status code equals 1.
Note that group subscriptions to specific sources may be rejected at
the destination network, and thus the composition of multicast
address records may differ from initial requests within an MLD (IGMP)
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Report Payload option.
5.5. Length Considerations: Number of Records and Addresses
Mobility Header Messages exchanged in HI/HACK and FBU/FBACK dialogs
impose length restrictions on multicast context records. The maximal
payload length available in FBU/FBACK messages is the PATH-MTU - 40
octets (IPv6 Header) - 6 octets (Mobility Header) - 6 octets (FBU/
FBACK Header). For example, on an Ethernet link with an MTU of 1500
octets, not more than 72 Multicast Address Records of minimal length
(without source states) may be exchanged in one message pair. In
typical handover scenarios, this number reduces further according to
unicast context and Binding Authorization data. A larger number of
MLD Report Payloads MAY be sent within multiple HI/HACK or FBU/FBACK
message pairs. In PFMIPv6, context information can be fragmented
over several HI/HACK messages. However, a single MLDv2 Report
Payload MUST NOT be fragmented. Hence, for a single Multicast
Address Record on an Ethernet link, the number of source addresses is
limited to 89.
5.6. MLD (IGMP) Compatibility Aspects
Access routers (MAGs) MUST support MLDv2 (IGMPv3). To enable
multicast service for MLDv1 (IGMPv2) listeners, the routers MUST
follow the interoperability rules defined in [RFC3810] ([RFC3376])
and appropriately set the Multicast Address Compatibility Mode. When
the Multicast Address Compatibility Mode is MLDv1 (IGMPv2), a router
internally translates the following MLDv1 (IGMPv2) messages for that
multicast address to their MLDv2 (IGMPv2) equivalents and uses these
messages in the context transfer. The current state of Compatibility
Mode is translated into the code of the Multicast Mobility Option as
defined in Section 5.3. A NAR (nMAG) receiving a Multicast Mobility
Option during handover will switch to the minimum obtained from its
previous and newly learned value of MLD (IGMP) Compatibility Mode for
continued operation.
6. Security Considerations
Security vulnerabilities that exceed issues discussed in the base
protocols of this document ([RFC5568], [RFC5949], [RFC3810],
[RFC3376]) are identified as follows.
Multicast context transfer at predictive handovers implements group
states at remote access routers and may lead to group subscriptions
without further validation of the multicast service requests.
Thereby a NAR (nMAG) is requested to cooperate in potentially complex
multicast re-routing and may receive large volumes of traffic.
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Malicious or inadvertent multicast context transfers may result in a
significant burden of route establishment and traffic management onto
the backbone infrastructure and the access router itself. Rapid re-
routing or traffic overload can be mitigated by a rate control at the
AR that restricts the frequency of traffic redirects and the total
number of subscriptions. In addition, the wireless access network
remains protected from multicast data injection until the requesting
MN attaches to the new location.
7. IANA Considerations
This document defines new flags and status codes in the HI and HAck
messages as well as two new mobility options. The Type values for
these mobility options are assigned from the same numbering space as
allocated for the other mobility options defined in [RFC3775]. Those
for the flags and status codes are assigned from the corresponding
numbering space defined in [RFC5568], or [RFC5949] and requested to
be created as new tables in the IANA registry (marked with
asterisks). New values for these registries can be allocated by
Standards Action or IESG approval [RFC5226].
8. Acknowledgments
Protocol extensions to support multicast in Fast Mobile IPv6 have
been loosely discussed since several years. Repeated attempts have
been taken to define corresponding protocol extensions. The first
draft [fmcast-mip6] was presented by Suh, Kwon, Suh, and Park already
in 2004.
This work was stimulated by many fruitful discussions in the MobOpts
research group. We would like to thank all active members for
constructive thoughts and contributions on the subject of multicast
mobility. Comments, discussions and reviewing remarks have been
contributed by (in alphabetical order) Carlos J. Bernardos, Luis M.
Contreras, Dirk von Hugo, Marco Liebsch, Behcet Sarikaya, Stig Venaas
and Juan Carlos Zuniga.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
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in IPv6", RFC 3775, June 2004.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
[RFC5568] Koodli, R., "Mobile IPv6 Fast Handovers", RFC 5568,
July 2009.
[RFC5949] Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F.
Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949,
September 2010.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.
[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.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
9.2. Informative References
[RFC5757] Schmidt, T., Waehlisch, M., and G. Fairhurst, "Multicast
Mobility in Mobile IP Version 6 (MIPv6): Problem Statement
and Brief Survey", RFC 5757, February 2010.
[fmcast-mip6]
Suh, K., Kwon, D., Suh, Y., and Y. Park, "Fast Multicast
Protocol for Mobile IPv6 in the fast handovers
environments", draft-suh-mipshop-fmcast-mip6-00 (work in
progress), July 2004.
[FMIPv6-Analysis]
Schmidt, TC. and M. Waehlisch, "Predictive versus Reactive
- Analysis of Handover Performance and Its Implications on
IPv6 and Multicast Mobility", Telecommunication
Systems Vol 33, No. 1-3, pp. 131-154, November 2005.
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[RFC6224] Schmidt, T., Waehlisch, M., and S. Krishnan, "Base
Deployment for Multicast Listener Support in Proxy Mobile
IPv6 (PMIPv6) Domains", RFC 6224, April 2011.
[RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", RFC 5844, May 2010.
[RFC5845] Muhanna, A., Khalil, M., Gundavelli, S., and K. Leung,
"Generic Routing Encapsulation (GRE) Key Option for Proxy
Mobile IPv6", RFC 5845, June 2010.
Appendix A. Change Log
The following changes have been made from
draft-schmidt-multimob-fmipv6-pfmipv6-multicast-04.
1. Following working group feedback, multicast traffic forwarding is
now a two-sided option between PAR (PMAG) and NAR (NMAG): Either
access router can decide on its contribution to the data plane.
2. Several editorial improvements.
The following changes have been made from
draft-schmidt-multimob-fmipv6-pfmipv6-multicast-03.
1. References updated.
The following changes have been made from
draft-schmidt-multimob-fmipv6-pfmipv6-multicast-02.
1. Detailed operations on PFMIPv6 entities completed.
2. Some editorial improvements & clarifications.
3. References updated.
The following changes have been made from
draft-schmidt-multimob-fmipv6-pfmipv6-multicast-01.
1. First detailed operations on PFMIPv6 added.
2. IPv4 support considerations for PFMIPv6 added.
3. Section on length considerations for multicast context records
corrected.
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4. Many editorial improvements & clarifications.
5. References updated.
The following changes have been made from
draft-schmidt-multimob-fmipv6-pfmipv6-multicast-00.
1. Editorial improvements & clarifications.
2. Section on length considerations for multicast context records
added.
3. Section on MLD/IGMP compatibility aspects added.
4. Security section added.
Authors' Addresses
Thomas C. Schmidt
HAW Hamburg
Dept. Informatik
Berliner Tor 7
Hamburg, D-20099
Germany
Email: schmidt@informatik.haw-hamburg.de
Matthias Waehlisch
link-lab & FU Berlin
Hoenower Str. 35
Berlin D-10318
Germany
Email: mw@link-lab.net
Rajeev Koodli
Cisco Systems
30 International Place
Xuanwu District,
Tewksbury MA 01876
USA
Email: rkoodli@cisco.com
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Godred Fairhurst
University of Aberdeen
School of Engineering
Aberdeen AB24 3UE
UK
Email: gorry@erg.abdn.ac.uk
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