Internet DRAFT - draft-ietf-mboned-v4v6-mcast-ps
draft-ietf-mboned-v4v6-mcast-ps
MBONED Working Group C. Jacquenet
Internet-Draft M. Boucadair
Intended status: Informational France Telecom Orange
Expires: March 10, 2014 Y. Lee
Comcast
J. Qin
Cisco Systems
T. Tsou
Huawei Technologies (USA)
Q. Sun
China Telecom
September 06, 2013
IPv4-IPv6 Multicast: Problem Statement and Use Cases
draft-ietf-mboned-v4v6-mcast-ps-04
Abstract
This document discusses issues and requirements raised by intra-
domain IPv4-IPv6 multicast interconnection and co-existence
scenarios. It also discusses various multicast use cases which may
occur during IPv6 transitioning.
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
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This Internet-Draft will expire on March 10, 2014.
Copyright Notice
Copyright (c) 2013 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Organization of the Document . . . . . . . . . . . . . . 4
2. Scope and Service Requirements . . . . . . . . . . . . . . . 5
2.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Service Requirements . . . . . . . . . . . . . . . . . . 5
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. IPv4 Receiver and Source Connected to an IPv6-Only
Network . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. IPv6 Receiver and Source Connected to an IPv4-Only
Network . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3. IPv6 Receiver and IPv4 Source . . . . . . . . . . . . . . 10
3.4. IPv4 Receiver and IPv6 Source . . . . . . . . . . . . . . 11
3.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 13
4. Design Requirements . . . . . . . . . . . . . . . . . . . . . 13
4.1. Group and Source Discovery Considerations . . . . . . . . 13
4.2. Subscription . . . . . . . . . . . . . . . . . . . . . . 14
4.3. Multicast Tree Computation . . . . . . . . . . . . . . . 14
4.4. Multicast Adaptation Functions (AF) . . . . . . . . . . . 14
4.4.1. AF For Control Flows . . . . . . . . . . . . . . . . 15
4.4.2. AF For Data Flows . . . . . . . . . . . . . . . . . . 16
4.4.3. Address Mapping . . . . . . . . . . . . . . . . . . . 16
4.5. Combination of ASM and SSM Modes . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
Global IPv4 address depletion inevitably challenges service providers
who must guarantee IPv4 service continuity during the forthcoming
transition period. In particular, access to IPv4 contents that are
multicast to IPv4 receivers becomes an issue when the forwarding of
multicast data assumes the use of global IPv4 addresses.
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The rarefaction of global IPv4 addresses may indeed affect the
multicast delivery of IPv4-formatted contents to IPv4 receivers. For
example, the observed evolution of ADSL broadband access
infrastructures from a service-specific, multi-PVC (Permanent Virtual
Circuit) scheme towards a "service-agnostic", single PVC scheme,
assumes the allocation of a globally unique IPv4 address on the WAN
(Wide Area Network) interface of the CPE (Customer Premises
Equipment), or to a mobile terminal), whatever the number and the
nature of the services the customer has subscribed to.
Likewise, the global IPv4 address depletion encourages the
development of IPv6 receivers while contents may very well remain
IPv4-formatted, i.e., sourced by an IPv4 application. There is
therefore a need to make sure such IPv6 receivers can access
IPv4-formatted contents during the transition period.
During the transition period, the usage of the remaining global IPv4
address blocks will have to be rationalized for the sake of IPv4
service continuity. The current state-of-the-art suggests the
introduction of NAT (Network Address Translation) capabilities
(generally denoted as CGN, for Carrier-Grade NAT) in providers'
networks, so that a global IPv4 address will be shared between
several customers.
As a consequence, CPE or mobile UE (User Equipment) devices will no
longer be assigned a dedicated global IPv4 address anymore, and IPv4
traffic will be privately-addressed until it reaches one of the CGN
capabilities deployed in the network. From a multicast delivery
standpoint, this situation suggests the following considerations:
o The current design of some multicast-based services like TV
broadcasting often relies upon the use of a private IPv4
addressing scheme because of a walled garden approach. Privately-
addressed IGMP [RFC2236][RFC3376] traffic sent by IPv4 receivers
is generally forwarded over a specific (e.g., "IPTV") PVC towards
an IGMP Querier located in the access infrastructure, e.g., in
some deployments it is hosted by a BRAS (BRoadband Access Server)
device that is the PPP (Point-to-Point Protocol) session endpoint
and which may also act as a PIM DR (Protocol Independent Multicast
Designated Router)[RFC4601]. This design does not suffer from
global IPv4 address depletion by definition (since multicast
traffic relies upon the use of a private IPv4 addressing scheme),
but it is inconsistent with migrating the access infrastructure
towards a publicly-addressed single PVC design scheme.
o Likewise, other deployments (e.g., cable operators' environments)
rely upon the public CPE's address for multicast delivery and will
therefore suffer from IPv4 address depletion.
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o The progressive introduction of IPv6 as the only perennial
solution to global IPv4 address depletion does not necessarily
assume that multicast-based IPv4 services will be migrated
accordingly. Access to IPv4 multicast contents when no global
IPv4 address can be assigned to a customer raises several issues:
(1) The completion of the IGMP-based multicast group subscription
procedure, (2) The computation of the IPv4 multicast distribution
tree, and (3) The IPv4-inferred addressing scheme to be used in a
networking environment which will progressively become
IPv6-enabled.
This document does not make any assumption on the techniques used for
the delivery of multicast traffic (e.g., native IP multicast with or
without traffic isolation features, etc.)
This document elaborates on the context and discusses multicast-
related issues and requirements.
1.1. Terminology
This document uses the following terms:
o Multicast Source: Source of contents that are multicast to
receivers. A video streaming server is an example of such source.
o Multicast Receiver: Receiver, in short. A Set Top Box (STB) is an
example of such receiver.
o Multicast Delivery Network: Network in short, covers the realm
from First Hop Routers that are directly connected to sources to
IGMP/MLD (Internet Group Management Protocol/Multicast Listener
Discovery) Querier devices that process IGMP/MLD signalling
traffic exchanged with receivers.
1.2. Organization of the Document
This document is organized as follows:
o Section 2 details basic requirements that should be addressed by
providers involved in the delivery of multicast-based services
during the transition period,
o Section 3 discusses several use cases that reflect issues raised
by the forthcoming transition period,
o Section 4 details design considerations.
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2. Scope and Service Requirements
2.1. Scope
Intra-domain only: The delivery of multicast services such as live
TV broadcasting often relies upon walled garden designs that
restrict the scope to the domain where such services can be
subscribed. As a consequence, considerations about inter-domain
multicast are out of the scope of this document.
Multicast-enabled networks only: This document assumes that the
network is IP multicast-enabled. That is, whatever the IP address
family of the content, this content will be multicast along
distribution trees that should be terminated as close to the
receivers as possible for the sake of bandwidth optimization. In
other words, considerations about forwarding multicast traffic
over unicast-only (access) networks are out of the scope of this
document.
Multicast to the receivers, not from the receivers: This document
only covers the case where multicast traffic is forwarded by the
service provider network to the receivers. The draft does not
consider multicast services that assume a source/receiver
heuristic, e.g., videoconferencing services. The draft primarily
focuses on residential multicast-based services, as per a typical
1:n group communication scheme.
2.2. Service Requirements
The delivery of multicast contents during the forthcoming transition
period needs to address the following requirements. Note that some
of these requirements are not necessarily specific to the IPv4-to-
IPv6 transition context, but rather apply to a wide range of
multicast-based services whatever the environmental constraints, but
the forthcoming transition period further stresses these requirements
(see Section 4.4.1 for more details).
o Optimize bandwidth. Contents should not be multicast twice (i.e.,
using both versions of IP) to optimize bandwidth usage. Injecting
multicast content using both IPv4 and IPv6 raises some
dimensioning issues that should be carefully evaluated by service
providers during network planning operations. For instance, if
only few IPv6-enabled receivers are in use, it can be more
convenient to convey multicast traffic over IPv4 rather than
doubling the consumed resources for few users. IPv4/IPv6 co-
existence solutions should be designed to optimize network
resource utilization.
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o Zap rapidly. The time it takes to switch from one content to
another must be as short as possible. For example, zapping times
between two TV channels should be comparable to an IPv4 case,
i.e., less than a second so that translation does not
significantly affect the overhead, whatever the conditions to
access the multicast network. A procedure called "IGMP fast-
leave" is sometimes used to minimize this issue so that the
corresponding multicast stream is stopped as soon as the IGMP
Leave message is received by the Querier. In current deployments,
IGMP fast-leave often assumes the activation of the IGMP Proxy
function in DSLAMs. The complexity of such design is aggravated
within a context where IPv4 multicast control messages are
encapsulated in IPv6.
o Preserve the integrity of contents that the user sees, i.e., not
the contents of IP packets. Some contract agreements may prevent
a service provider from altering the content owned by the content
provider, because of copyright, confidentiality and SLA assurance
reasons. Multicast streams should be delivered without altering
their content.
o Preserve service quality. Crossing a CGN or performing multicast
packet encapsulation may lead to fragmentation or extra delays and
may therefore impact the perceived quality of service. Such
degradation must be avoided.
o Optimize IPv4-IPv6 inter-working design. In some operational
networks, a source-based stateful NAT function is sometimes used
for load balancing purposes, for example. Because of the
operational issues raised by such a stateful design, the
deployment of stateless IPv4-IPv6 interworking functions should be
privileged.
3. Use Cases
During the IPv4-to-IPv6 transition period, there might be a mix of
multicast receivers, sources, and networks running in different
address families. However, service providers must guarantee the
delivery of multicast services to IPv4 receivers and, presumably,
IPv6 receivers. Because of the inevitable combination of different
IP version-related environments (sources, receivers and networks),
service providers should carefully plan and choose the appropriate
technique that will optimize the network resources to deliver
multicast-based services.
Concretely, several use cases can be considered during the IPv4/ IPv6
co-existence period. Some of them are depicted in the following sub-
sections.
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Note that the following diagrams are meant to illustrate the
conceptual model. As such, they do not necessarily mean that the
Adaptation Functions (AF) are embedded in a separate device and that
messages need to be explicitly translated into new messages.
3.1. IPv4 Receiver and Source Connected to an IPv6-Only Network
We refer to this scenario as 4-6-4. An example of such use case is a
DS-Lite environment, where customers will share global IPv4
addresses. IPv4 receivers are connected to CPE devices that are
provisioned with an IPv6 prefix only. Delivering multicast content
sent by an IPv4 source to such receivers requires the activation of
some adaptation functions (AFs). These may operate at the network
layer (interworking functions (IWF) or at the application layer
(application level gateways (ALGs)).
The signalling flow for the 4-6-4 use case is shown in Figure 1.
+------+ +-----+ +------+ +------+
| Host | IGMP | DS | | MR | PIM | MR |
| Rcvr |------| AF1 | | | . . . . | |
| | IPv4 | | | (BG) | IPv4 | (DR) |
+------+ +-----+ +------+ +------+
/ \
MLD / IPv6 PIM \ IPv4
/ \
+------+ +----+ +------+
| MR | PIM | | PIM | DS |
| |------| MR | . . . | AF2 |
| (DR) | IPv6 | | IPv6 | (BG) |
+------+ +----+ +------+
------------------------------------->
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function (ALG or IWF)
MR : Multicast Router
DR : Designated Router
BG : Border Gateway
Figure 1: Signalling Path for the 4-6-4 Scenario.
AF1 refers to an IGMP/MLD Adaptation Function. Another Adaptation
Function AF2 is needed at the border between the IPv6 multicast
domain and the IPv4 multicast domain where the source resides. AF2
is typically embedded in a multicast router that either terminates or
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propagates PIM signalling directed toward the IPv4 source in the IPv6
multicast domain.
On the IPv4 side, AF2 also acts as a multicast router, and uses PIMv4
signalling to join the IPv4 multicast group. The return path taken
by multicast traffic is shown in Figure 2.
+------+ +-----+ +------+ +------+ +-----+
| Host | | DS | | MR | | MR | | |
| Rcvr |------| AF1 | | | . . . | |------| Src |
| | IPv4 | | | (BG) | IPv4 | (DR) | IPv4 | |
+------+ +-----+ +------+ +------+ +-----+
/ \
/ IPv6 \ IPv4
/ \
+------+ +----+ +------+
| MR | | | | DS |
| |------| MR | . . . | AF2 |
| (DR) | IPv6 | | IPv6 | (BG) |
+------+ +----+ +------+
<-------------------------------------
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast router
DR : Designated Router
BG : Border Gateway
Src : Multicast source
Figure 2: Multicast Traffic Forwarding Path for the 4-6-4 Scenario.
Again, adaptation functions are needed whenever the IP protocol
version changes. The adaptation function instance AF2 at the
boundary between the source network and the IPv6 network may either
encapsulate or translate the headers of the IPv4 packets to allow the
content to cross the IPv6 network. The adaptation function instance
at the boundary between the IPv6 network and the receiver network
performs the reverse operation to deliver IPv4 packets.
Given the current state-of-the-art where multicast content is likely
to remain IPv4-formatted while receiver devices such as Set Top Boxes
will also remain IPv4-only for quite some time, this scenario is
prioritized by some service providers, including those that are
deploying or will deploy DS-Lite CGN capabilities for the sake of
IPv4 service continuity.
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3.2. IPv6 Receiver and Source Connected to an IPv4-Only Network
We refer to this scenario as 6-4-6. Since providers who own the
multicast content may not be ready for IPv6 migration beofre some
time, the content is likely to remain IPv4-formatted. As a
consequence, this 6-4-6 scenario is of lower priority than the 4-6-4
scenario.
The signalling path for the 6-4-6 scenario is illustrated in Figure
3.
+------+ +-----+ +------+ +------+
| Host | MLD | DS | | MR | PIM | MR |
| Rcvr |------| AF1 | | | . . . . | |
| | IPv6 | | | (BG) | IPv6 | (DR) |
+------+ +-----+ +------+ +------+
/ \
IGMP / IPv4 PIM \ IPv6
/ \
+------+ +----+ +------+
| MR | PIM | | PIM | DS |
| |------| MR | . . . | AF2 |
| (DR) | IPv4 | | IPv4 | (BG) |
+------+ +----+ +------+
------------------------------------->
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast Router
DR : Designated Router
BG : Border Gateway
Figure 3: Signalling Path For the 6-4-6 Scenario.
Figure 4 shows the path taken by multicast traffic flowing from the
IPv6 source to the IPv6 receiver.
+------+ +-----+ +------+ +------+
| Host | | DS | | MR | | MR |
| Rcvr |------| AF1 | | | . . . | |
| | IPv6 | | | (BG) | IPv6 | (DR) |
+------+ +-----+ +------+ +------+
/ \ \
/ IPv4 \ IPv6 \ IPv6
/ \ \
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+------+ +----+ +------+ +-----+
| MR | | | | DS | | |
| |------| MR | . . . | AF2 | | Src |
| (DR) | IPv4 | | IPv4 | (BG) | | |
+------+ +----+ +------+ +-----+
<-------------------------------------
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast Router
DR : Designated Router
BG : Border Gateway
Src : Multicast source
Figure 4: Multicast Traffic Forwarding Path For the 6-4-6 Scenario.
3.3. IPv6 Receiver and IPv4 Source
We refer to this scenario as 6-4. An example of such use case is the
context of some mobile networks, where terminal devices are only
provisioned with an IPv6 prefix. Accessing IPv4-formatted multicast
content from an IPv6-only receiver requires additional functions to
be enabled.
This scenario is privileged by mobile operators who deploy NAT64
capabilities in their network. It is illustrated in Figures 5
(signalling path) and 6 (forwarding of multicast traffic). Only one
adaptation function instance is needed, and it will be located at the
IPv4/IPv6 multicast domain boundary.
+------+ +------+ +------+
| Host | | MR | PIM | MR |
| Rcvr | | | . . . . | |
| | | (BG) | IPv4 | (DR) |
+------+ +------+ +------+
\ \
MLD \ IPv6 PIM \ IPv4
\ \
+------+ +----+ +------+
| MR | PIM | | PIM | DS |
| |------| MR | . . . | AF1 |
| (DR) | IPv6 | | IPv6 | (BG) |
+------+ +----+ +------+
------------------------------------->
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Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast Router
DR : Designated Router
BG : Border Gateway
Figure 5: Signalling Path For the 6-4 Scenario.
+------+ +------+ +------+
| Host | | MR | | MR |
| Rcvr | | | . . . . | |
| | | (BG) | IPv4 | (DR) |
+------+ +------+ +------+
\ \ \
\ IPv6 \ IPv4 \ IPv4
\ \ \
+------+ +----+ +------+ +-----+
| MR | | | | DS | | |
| |------| MR | . . . | AF1 | | Src |
| (DR) | IPv6 | | IPv6 | (BG) | | |
+------+ +----+ +------+ +-----+
<-------------------------------------
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast Router
DR : Designated Router
BG : Border Gateway
Src : Multicast source
Figure 6: Multicast Traffic Forwarding Path For the 6-4 Scenario.
3.4. IPv4 Receiver and IPv6 Source
We refer to this scenario as 4-6. Yet, multicast sources are likely
to remain IPv4-enabled in a first stage; therefore, the content is
likely to remain IPv4-formatted. As a consequence, this scenario is
unlikely to occur during the first years of the transition period.
The signalling path for this scenario is shown in Figure 7. The
multicast traffic forwarding path is shown in Figure 8. There are
similarities with the 6-4 scenario but address mapping across IP
version boundaries is more challenging.
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+------+ +------+ +------+
| Host | | MR | PIM | MR |
| Rcvr | | | . . . . | |
| | | (BG) | IPv6 | (DR) |
+------+ +------+ +------+
\ \
IGMP \ IPv4 PIM \ IPv6
\ \
+------+ +----+ +------+
| MR | PIM | | PIM | DS |
| |------| MR | . . . | AF1 |
| (DR) | IPv4 | | IPv4 | (BG) |
+------+ +----+ +------+
------------------------------------->
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast Router
DR : Designated Router
BG : Border Gateway
Figure 7: Signalling Path For the 4-6 Scenario.
+------+ +------+ +------+
| Host | | MR | | MR |
| Rcvr | | | . . . . | |
| | | (BG) | IPv6 | (DR) |
+------+ +------+ +------+
\ \ \
\ IPv4 \ IPv6 \ IPv6
\ \ \
+------+ +----+ +------+ +-----+
| MR | | | | DS | | |
| |------| MR | . . . | AF1 | | Src |
| (DR) | IPv4 | | IPv4 | (BG) | | |
+------+ +----+ +------+ +-----+
<-------------------------------------
Rcvr: Multicast receiver
DS : Dual Stack
AF : Adaptation Function
MR : Multicast Router
DR : Designated Router
BG : Border Gateway
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Src : Multicast source
Figure 8: Multicast Traffic Forwarding Path For the 4-6 Scenario.
3.5. Summary
To summarize, the use cases of highest priority are those involving
IPv4 sources, i.e., the 4-6-4 and 6-4 scenarios.
4. Design Requirements
4.1. Group and Source Discovery Considerations
Multicast applications that embed address information in the payload
may require Application Level Gateway (ALG) during the transition
period. An ALG is application-specific by definition, and may
therefore be unnecessary depending on the nature of the multicast
service.
Such ALG (Application Level Gateway) may also be required to help an
IPv6 receiver select the appropriate multicast group address when
only the IPv4 address is advertised (e.g., when the SDP (Session
Description Protocol) protocol is used to advertise some contents);
otherwise, access to IPv4 multicast content from an IPv6 receiver may
be compromised.
ALGs may be located upstream in the network. As a consequence, these
ALGs do not know in advance whether the receiver is dual-stack or
IPv6-only. In order to avoid the use of an ALG in the path, an
IPv4-only source can advertise both an IPv4 multicast group address
and the corresponding IPv4-embedded IPv6 multicast group address
[I-D.ietf-mboned-64-multicast-address-format].
However, a dual-stack receiver may prefer to use the IPv6 address to
receive the multicast content. The selection of the IPv6 multicast
address would then require multicast flows to cross an IPv4-IPv6
interworking function.
The receiver should therefore be able to unambiguously distinguish an
IPv4-embedded IPv6 multicast address from a native IPv6 multicast
address.
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4.2. Subscription
Multicast distribution trees are receiver-initiated. IPv4 receivers
that want to subscribe to an IPv4 multicast group will send IGMP
Report messages accordingly. In case the underlying access network
is IPv6, the information conveyed in IGMP messages should be relayed
by corresponding MLD messages.
4.3. Multicast Tree Computation
Grafting to an IPv4 multicast distribution tree through an IPv6
multicast domain suggests that IPv4 multicast traffic will have to be
conveyed along an "IPv6-equivalent" multicast distribution tree.
That is, part of the multicast distribution tree along which IPv4
multicast traffic will be forwarded should be computed and maintained
by means of the PIMv6 machinery, so that the distribution tree can be
terminated as close to the IPv4 receivers as possible for the sake of
the multicast forwarding efficiency.
This assumes a close interaction between the PIM designs enforced in
both IPv4 and IPv6 multicast domains, by means of specific Inter-
Working Functions that are further discussed in Section 4.4.
Such interaction may be complicated by different combinations: the
IPv4 multicast domain is SSM-enabled (with no RP (Rendezvous Point)
routers), while the IPv6 multicast domain may support both ASM (Any
Source Multicast) and SSM (Source Specific Multicast) [RFC3569]
modes.
4.4. Multicast Adaptation Functions (AF)
IPv4-IPv6 multicast interworking functions are required for both
translation (one address family to another) and traversal (one
address family over another) contexts.
Given the multiple versions of Group Membership management protocols,
issues may be raised when, for example, IGMPv2 is running in the IPv4
multicast domain that is connected to the IPv6 multicast domain by
means of an IWF, while MLDv2 is running in the IPv6 multicast domain.
To solve these problems, the design of the IWF function should adhere
to the IP version-independent, protocol interaction approach
documented in Section 8 of [RFC3810] and Section 7 of [RFC3376].
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Note that, for traversal cases, to improve the efficiency of the
multicast service delivery, traffic will be multicast along
distribution trees that should be terminated as close to the
receivers as possible for bandwidth optimization purposes. As a
reminder, the traversal of unicast-only (access) networks is not
considered in this document.
4.4.1. AF For Control Flows
The IWF to process multicast signalling flows (such as IGMP or MLD
Report messages) should be independent of the IP version and consist
mainly of an IPv4-IPv6 adaptation element and an IP address
translation element. The message format adaptation must follow what
is specified in [RFC3810] or [RFC4601], and the device that embeds
the IWF device must be multicast-enabled, i.e., support IGMP, MLD and
/or PIM, depending on the context (address family-wise) and the
design (e.g., this device could be a PIM DR in addition to a MLD
Querier).
The IWF can then be operated in the following modes: IGMP-MLD,
PIMv4-PIMv6, MLD-PIMv4 and IGMP-PIMv6. In particular, Source-
Specific Multicast (SSM) must be supported (i.e., IGMPv3/MLDv2
signalling traffic as well as the ability to directly send PIM (S, G)
Join messages towards the source).
The following sub-sections describe some interworking functions which
may be solicited, depending on the environment. Note that it may not
be a stand-alone IWF that simply translates messages, but, for
example, the combination of IPv4 and IPv6 states that would trigger
the forwarding of aggregated MLD Report messages upstream that would
include IPv6 groups based upon IPv4 states.
4.4.1.1. IGMP-MLD Interworking
The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying
function specified in [RFC4605] and the IGMP/MLD adaptation function
which is meant to reflect the contents of IGMP messages into MLD
messages, and vice versa.
For example, when an IGMP Report message is received to subscribe to
a given multicast group (which may be associated to a source address
if SSM mode is used), the IGMP-MLD Interworking Function must send an
MLD Report message to subscribe to the corresponding IPv6 multicast
group.
4.4.1.2. IPv4-IPv6 PIM Interworking
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[RFC4601] allows the computation of PIM-based IPv4 or IPv6
distribution trees; PIM is IP version agnostic. There is no specific
IPv6 PIM machinery that would work differently than an IPv4 PIM
machinery. The new features needed for the IPv4-IPv6 PIM
Interworking Function consist in dynamically triggering the PIM
message of Address Family 1 upon receipt of the equivalent PIM
message of Address Family 2.
The address mapping must be performed similarly to that of the IGMP-
MLD Interworking Function.
4.4.1.3. MLD-IPv4 PIM Interworking
This IWF function is required when the MLD Querier is connected to an
IPv4 PIM domain.
The address mapping must be performed similarly to that of the IGMP-
MLD Interworking Function.
4.4.1.4. IGMP-IPv6 PIM Interworking
The address mapping must be performed similarly to that of the IGMP-
MLD Interworking Function.
4.4.2. AF For Data Flows
The IWF to be used for multicast data flows is operated at the
boundary between IPv4 and IPv6 multicast networks. Either
encapsulation/de-capsulation or translation modes can be enforced,
depending on the design. Note that translation operations must
follow the algorithm specified in [RFC6145].
4.4.3. Address Mapping
The address mapping mechanisms to be used in either a stateful or
stateless fashion need to be specified for the translation from one
address family to the other.
The address formats can be those defined in
[I-D.ietf-mboned-64-multicast-address-format] and [RFC6052] for
IPv4-embedded IPv6 multicast and unicast addresses. Mapping
operations are performed in a stateless manner by the algorithms
specified in the aforementioned documents.
In this context, the IPv6 prefixes required for embedding IPv4
addresses can be assigned to devices that support IWF features by
various means (e.g., static or dynamic configuration, out-of-band
mechanisms, etc.).
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If stateful approaches are used, it is recommended to carefully
investigate the need to synchronize mapping states between multiple
boxes, and the coordination of the IWF and source/group discovery
elements is also required, at the cost of extra complexity.
4.5. Combination of ASM and SSM Modes
The ASM (Any Source Multicast) mode could be used to optimize the
forwarding of IPv4 multicast traffic sent by different sources into
the IPv6 multicast domain by selecting RP routers that could be
located at the border between the IPv6 and the IPv4 multicast
domains. This design may optimize the multicast forwarding
efficiency in the IPv6 domain when access to several IPv4 multicast
sources needs to be granted.
5. IANA Considerations
This document makes no request to IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
Access to contents in a multicast-enabled environment raises
different security issues that have been already documented. In
particular:
o When translating ASM-SSM there are certain security expectations
from SSM (only receiving from the single specified sender), which
are not the same expectations that come from ASM.
o If mappings are not stateful, it may be harder to monitor and
troubleshoot the traffic.
o There are concepts of IPv4 and IPv6 multicast scopes. When
translating, it must be taken into account how to reasonably map
between scopes, and it is important that the scopes are configured
appropriately on the routers so that a scope intended to be within
a site for IPv4 (for example), doesn't leak outside the site due
to translation to IPv6 inside the site.
7. Acknowledgments
Special thanks to T. Taylor for providing the figures and some of the
text that illustrate the use cases depicted in Section 3. Thanks
also to H. Asaeda, M. Blanchet, M. Eubanks, B. Haberman, N. Leymann,
S. Perrault and S. Venaas for their valuable comments and support.
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8. References
8.1. Normative References
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, November 1997.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3569] Bhattacharyya, S., "An Overview of Source-Specific
Multicast (SSM)", RFC 3569, July 2003.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[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.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
8.2. Informative References
[I-D.ietf-mboned-64-multicast-address-format]
Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X., and
M. Xu, "IPv6 Multicast Address With Embedded IPv4
Multicast Address", draft-ietf-mboned-64-multicast-
address-format-05 (work in progress), April 2013.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
Authors' Addresses
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Christian Jacquenet
France Telecom Orange
4 rue du Clos Courtel
Cesson-Sevigne 35512
France
Phone: +33 2 99 12 43 82
Email: christian.jacquenet@orange.com
Mohamed Boucadair
France Telecom Orange
4 rue du Clos Courtel
Cesson-Sevigne 35512
France
Phone: +33 2 99 12 43 71
Email: mohamed.boucadair@orange.com
Yiu Lee
Comcast
US
Email: Yiu_Lee@Cable.Comcast.com
Jacni Qin
Cisco Systems
People's Republic of China
Email: jacni@jacni.com
Tina Tsou
Huawei Technologies (USA)
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1 408 330 4424
Email: tena@huawei.com
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Qiong Sun
China Telecom
Room 708, No.118, Xizhimennei Street
Beijing 100035
People's Republic of China
Phone: >+86-10-58552936
Email: sunqiong@ctbri.com.cn
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