| Softwire WG | J. Qin |
| Internet-Draft | Cisco |
| Intended status: Standards Track | M. Boucadair |
| Expires: March 3, 2016 | C. Jacquenet |
| France Telecom | |
| Y. Lee | |
| Comcast | |
| Q. Wang | |
| China Telecom | |
| August 31, 2015 |
Delivery of IPv4 Multicast Services to IPv4 Clients over an IPv6 Multicast Network
draft-ietf-softwire-dslite-multicast-10
This document specifies a solution for the delivery of IPv4 multicast services to IPv4 clients over an IPv6 multicast network. The solution relies upon a stateless IPv4-in-IPv6 encapsulation scheme and uses the IPv6 multicast distribution tree to deliver IPv4 multicast traffic. The solution is particularly useful for the delivery of multicast service offerings to DS-Lite serviced customers.
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 March 3, 2016.
Copyright (c) 2015 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.
DS-Lite [RFC6333] is a technique that rationalizes the usage of the remaining global IPv4 addresses during the transition period by sharing a single IPv4 address with multiple users. A typical DS-Lite scenario is the delivery of an IPv4 service to an IPv4 user over an IPv6 network (denoted as a 4-6-4 scenario). [RFC6333] covers unicast services exclusively.
This document specifies a generic solution for delivery of IPv4 multicast services to IPv4 clients over an IPv6 multicast network. The solution was developed with DS-Lite in mind (see more discussion below). The solution is however not limited to DS-Lite.
If customers have to access IPv4 multicast-based services through DS-Lite environment, Address Family Transition Router (AFTR) devices will have to process all the IGMP Report messages [RFC2236] [RFC3376] that have been forwarded by the CPE into the IPv4-in-IPv6 tunnels. From that standpoint, AFTR devices are likely to behave as a replication point for downstream multicast traffic. And the multicast packets will be replicated for each tunnel endpoint where IPv4 receivers are connected to.
This kind of DS-Lite environment raises two major issues:
This document specifies an extension to the DS-Lite model to deliver IPv4 multicast services to IPv4 clients over an IPv6 multicast-enabled network.
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].
This document makes use of the following terms:
This document focuses only on subscription to an IPv4 multicast group and the delivery of IPv4-formatted content to IPv4 receivers over an IPv6-only network. In particular, only the following case is covered:
This document does not cover the source/receiver heuristics, where as IPv4 receiver can also behave as an IPv4 multicast source. This document assumes that hosts behind the mB4 are IPv4 multicast receivers only.
In the original DS-Lite specification [RFC6333], an IPv4-in-IPv6 tunnel is used to carry bidirectional IPv4 unicast traffic between a B4 and an AFTR. The solution specified in this document provides an IPv4-in-IPv6 encapsulation scheme to deliver unidirectional IPv4 multicast traffic from an mAFTR to an mB4.
An overview of the solution is provided in this section which is intended as an introduction to how it works, but is NOT normative. For the normative specifications of the two new functional elements: mB4 and mAFTR (Figure 1), refer to Section 6 and Section 7.
------------
/ \
| IPv4 network |
\ /
------------
IPv4 multicast : | ^ PIMv4 Join
v | :
+-------------+
| mAFTR |
+-------------+
IPv6 multicast |:| | ^ PIMv6 Join (PIMv6
(IPv4 embedded) |:| | : routers in between)
------------
/ \
| IPv6 network |
\ /
------------
|:| | : MLD Report
|v| | :
+-----------+
| mB4 |
+-----------+
IPv4 multicast : | ^ IGMP Report
v | :
+-----------+
| IPv4 |
| receiver |
+-----------+
Figure 1: Functional Architecture
In order to map the addresses of IPv4 multicast traffic with IPv6 multicast addresses, an IPv6 multicast prefix (mPrefix64) and an IPv6 unicast prefix (uPrefix64) are provided to mAFTR and mB4 elements, both of which contribute to the computation and the maintenance of the IPv6 multicast distribution tree that extends the IPv4 multicast distribution tree into the IPv6 multicast network.
The mAFTR and mB4 use mPrefix64 to convert an IPv4 multicast address (G4) to an IPv4-embedded IPv6 multicast address (G6). The mAFTR and mB4 use uPrefix64 to convert an IPv4 multicast source address (S4) to an IPv4-embedded IPv6 address (S6). The mAFTR and mB4 MUST use the same mPrefix64 and uPrefix64, as well as run the same algorithm for building IPv4-embedded IPv6 addresses. Refer to Section 5 for more details about the address mapping.
When an IPv4 receiver connected to the device that embeds the mB4 capability wants to subscribe to an IPv4 multicast group, it sends an IGMP Report message to the mB4. The mB4 creates the IPv6 multicast group (G6) address using mPrefix64 and the original IPv4 multicast group address. If the receiver sends a source-specific IGMPv3 Report message, the mB4 will create the IPv6 source address (S6) using uPrefix64 and the original IPv4 source address.
The mB4 uses the G6 (and both S6 and G6 in SSM) to create the corresponding MLD Report message. The mB4 sends the Report message to the MLD Querier in the IPv6 network. The MLD Querier (typically acts as the PIMv6 Designated Router) receives the MLD Report message and sends the PIMv6 Join to join the IPv6 multicast distribution tree. The MLD Querier can send either PIMv6 Join (*,G6) in ASM or PIMv6 Join (S6,G6) in SSM to the mAFTR.
The mAFTR acts as the DR to which the uPrefix64-derived S6 is connected. The mAFTR will receive the source-specific PIMv6 Join message (S6,G6) from the IPv6 multicast network. If the mAFTR is the Rendezvous Point (RP) of G6, it will receive the any-source PIMv6 Join message (*,G6) from the IPv6 multicast network. If the mAFTR is not the RP of G6, it will send the PIM Register message to the RP of G6 located in the IPv6 multicast network.
When the mAFTR receives the PIMv6 Join message (*,G6), it will extract the IPv4 multicast group address (G4). If the mAFTR is the RP of G4 in the IPv4 multicast network, it will create a (*,G4) entry (if there is not yet an existing one) in its own IPv4 multicast routing table. If the mAFTR is not the RP of G4, it will send the corresponding PIMv4 Join message (*,G4) towards the RP of G4 in the IPv4 multicast network.
When the mAFTR receives the PIMv6 Join message (S6,G6), it will extract the IPv4 multicast group address (G4) and IPv4 source address (S4) and send the corresponding (S4,G4) PIMv4 Join message directly to the IPv4 source.
A branch of the multicast distribution tree is constructed, comprising both an IPv4 part (from the mAFTR upstream) and an IPv6 part (from mAFTR downstream to the mB4).
The mAFTR MUST advertise the route of uPrefix64 with an IPv6 IGP, so as to represent the IPv4-embedded IPv6 source in the IPv6 multicast network, and to pass the Reverse Path Forwarding (RPF) check on multicast devices.
When the mAFTR receives an IPv4 multicast packet, it will encapsulate the packet into an IPv6 multicast packet using the IPv4-embedded IPv6 multicast address as the destination address and an IPv4-embedded IPv6 unicast address as the source address. The encapsulated IPv6 multicast packet will be forwarded down the IPv6 multicast distribution tree and the mB4 will eventually receive the packet.
The IPv6 multicast network treats the IPv4-in-IPv6 encapsulated multicast packets as native. The IPv6 multicast routers use the outer IPv6 header to make forwarding decisions.
When the mB4 receive the IPv6 multicast packet (to G6) derived by mPrefix64, it MUST decapsulate it and forward the original IPv4 multicast packet to the receivers subscribing to G4.
Note: At this point, only IPv4-in-IPv6 encapsulation is defined; however, other types of encapsulation could be defined in the future.
A dedicated IPv6 multicast prefix (mPrefix64) is provisioned to the mAFTR and the mB4. The mAFTR and the mB4 use the mPrefix64 to form an IPv6 multicast group address from an IPv4 multicast group address. The mPrefix64 can be of two types: ASM_mPrefix64 (a mPrefix64 used in ASM mode) or SSM_mPrefix64 (a mPrefix64 used in SSM mode). The mPrefix64 MUST be derived from the corresponding IPv6 multicast address space (e.g., the SSM_mPrefix64 MUST be in the range of multicast address space specified in [RFC4607]).
The IPv6 part of the multicast distribution tree can be seen as an extension of the IPv4 part of the multicast distribution tree. The IPv4 multicast source address MUST be mapped to an IPv6 multicast source address. An IPv6 unicast prefix (uPrefix64) is provisioned to the mAFTR and the mB4. The mAFTR and the mB4 use the uPrefix64 to form an IPv6 multicast source address from an IPv4 multicast source address. The uPrefix-formed IPv6 multicast source address will represent the original IPv4 multicast source in the IPv6 multicast network. The uPrefix64 MUST be derived from the IPv6 unicast address space.
The address translation MUST follow the algorithm defined in Section 5.2.
The mPrefix64 and uPrefix64 can be configured in the mB4 using a variety of methods, including an out-of-band mechanism, manual configuration, or a dedicated provisioning protocol (e.g., using DHCPv6 [I-D.ietf-softwire-multicast-prefix-option]).
IPv4-Embedded IPv6 multicast addresses are composed according to the following algorithm:
The IPv4 multicast addresses are extracted from the IPv4-Embedded IPv6 Multicast Addresses according to the following algorithm:
An IPv4 source is represented in the IPv6 realm with its IPv4-converted IPv6 address [RFC6052].
The embedded IPv4 address in an IPv6 multicast address is included in the last 32 bits; therefore dotted decimal notation can be used.
Group address mapping example:
+---------------------+--------------+----------------------------+
| mPrefix64 | IPv4 address | IPv4-Embedded IPv6 address |
+---------------------+--------------+----------------------------+
| ff0x::db8:0:0/96 | 233.252.0.1 | ff0x::db8::233.252.0.1 |
+---------------------+--------------+----------------------------+
Source address mapping example when a /96 is used:
+---------------------+--------------+----------------------------+
| uPrefix64 | IPv4 address | IPv4-Embedded IPv6 address |
+---------------------+--------------+----------------------------+
| 2001:db8::/96 | 192.0.2.33 | 2001:db8::192.0.2.33 |
+---------------------+--------------+----------------------------+
IPv4 and IPv6 addresses used in this example are derived from the IPv4 and IPv6 blocks reserved for documentation, as per [RFC6676]. The unicast IPv4 address of the above example is derived from the documentation address block defined in [RFC6890].
The IGMP-MLD Interworking Function combines the IGMP/MLD Proxying function and the address synthesizing operations. The IGMP/MLD Proxying function is specified in [RFC4605]. The address translation is stateless and MUST follow the address mapping specified in Section 5.
The mB4 with the IGMP-MLD Interworking Function embedded relays between the IGMP domain and the MLD domain. The mB4 performs the host portion of the MLD protocol on the upstream interface. The composition of IPv6 membership in this context is constructed through address synthesizing operations and MUST synchronize with the membership database maintained in the IGMP domain. MLD messages will be forwarded natively towards the MLD Querier located upstream in the IPv6 network. The mB4 also performs the router portion of the IGMP protocol on the downstream interface(s). Refer to [RFC4605] for more details
+----------+ IGMP +-------+ MLD +---------+
| IPv4 |---------| mB4 |---------| MLD |
| Receiver | | | | Querier |
+----------+ +-------+ +---------+
Figure 2: IGMP-MLD Interworking
If SSM is deployed, the mB4 MUST construct the IPv6 source address (or retrieve the IPv4 source address) using the uPrefix64. The mB4 may create a membership database which associates the IPv4-IPv6 multicast groups with the interfaces (e.g., Wi-Fi and Wired Ethernet) facing IPv4 multicast receivers.
When the mB4 receives an IPv6 multicast packet, it MUST check the group address and the source address. If the IPv6 multicast group prefix is mPrefix64 and the IPv6 source prefix is uPrefix64, the mB4 MUST de-capsulate the IPv6 header and forward the IPv4 multicast packet through each relevant interface. Otherwise, the mB4 MUST drop the packet silently.
As an illustration, if a packet is received from source 2001:db8::192.0.2.33 and to be forwarded to group ff3x:1000::233.252.0.1, the mB4 will de-capsulate it into an IPv4 multicast packet using 192.0.2.33 as the IPv4 multicast source address and using 233.252.0.1 as the IPv4 destination address.
Encapsulating IPv4 multicast packets into IPv6 multicast packets that will be forwarded by the mAFTR to the mB4 along the IPv6 multicast distribution tree reduces the effective MTU size by the size of an IPv6 header. In this specification, the data flow is unidirectional from mAFTR to mB4, the mAFTR MUST fragment the oversized IPv6 packet after the encapsulation into two IPv6 packets. The mB4 MUST reassemble the IPv6 packets, decapsulate the IPv6 packet, and forward the IPv4 packet to the hosts subscribing the multicast group. Further considerations about fragmentation issues are documented in [RFC6333].
If the mB4 function is implemented in the host which is directly connected to an IPv6-only network, the host MUST implement Section 6.1, Section 6.2, and Section 6.3. The host MAY optimize the implementation to provide an Application Programming Interface (API) or kernel module to skip the IGMP-MLD Interworking Function. The optimization is out of scope of the specification.
When several mPrefix64s are available, if each enclosed IPv4-embedded IPv6 multicast prefix has a distinct scope, mB4 MUST select the appropriate IPv4-embedded IPv6 multicast prefix having a scope matching the IPv4 multicast address used to synthesize an IPv4-embedded IPv6 multicast address.
The mB4 MAY be configured to not preserve the scope when enforcing the address translation algorithm.
The mAFTR is responsible for interconnecting the IPv4 multicast distribution tree with the corresponding IPv6 multicast distribution tree. The mAFTR MUST use the uPrefix64 to build the IPv6 source addresses of the multicast group address derived from mPrefix64. In other words, the mAFTR MUST be the multicast source derived from uPrefix64.
The mAFTR MUST advertise the route of uPrefix64 to the IPv6 IGP. This is needed for the IPv6 multicast routers to have routing information to discover the source.
The mAFTR MUST interwork PIM Join/Prune messages for (*, G6) and (S6, G6) on their corresponding (*, G4) and (S4, G4). The following text specifies the expected behavior of mAFTR for PIM Join message.
+---------+
---------| mAFTR |---------
PIMv6 |uPrefix64| PIMv4
|mPreifx64|
+---------+
Figure 3: PIMv6-PIMv4 Interworking Function
The mAFTR contains two separate Tree Information Base (TIB): IPv4 Tree Information Base (TIB4) and IPv6 Tree Information Base (TIB6), which are bridged by one IPv4-in-IPv6 virtual interface. It should be noted that the implementations may vary (e.g., using one integrated TIB without any virtual interface), while they should follow the specification herein for the consistency of overall functionality.
When a mAFTR receives a PIMv6 Join message (*,G6) with an IPv6 multicast group address (G6) that is derived from the mPrefix64, it MUST check its IPv6 Tree Information Base (TIB6). If there is an entry for this G6, it MUST check whether the interface through which the PIMv6 Join message has been received is on the outgoing interface list. If not, the mAFTR MUST add the interface to the outgoing interface list. If there is no entry in the TIB6, the mAFTR MUST create a new entry (*,G6) for the multicast group. While, whether or not to set the IPv4-in-IPv6 virtual interface as the incoming interface of the newly created entry is up to the implementation but should comply with the mAFTR's behavior of multicast data forwarding, see Section 7.4.
The mAFTR MUST extract the IPv4 multicast group address (G4) from the IPv4-embedded IPv6 multicast address (G6) contained in the PIMv6 Join message. The mAFTR MUST check its IPv4 Tree Information Base (TIB4). If there is an entry for G4, it MUST check whether the IPv4-in-IPv6 virtual interface is on the outgoing interface list. If not, the mAFTR MUST add the interface to the outgoing interface list. If there is no entry for G4, the mAFTR MUST create a new (*,G4) entry in its TIB4 and initiate the procedure for building the shared tree in the IPv4 multicast network without any additional requirement.
If mAFTR receives a source-specific Join message, the (S6, G6) will be processed rather than (*,G6). The procedures of processing (S6,G6) and (*,G6) are almost the same. Differences have been detailed in [RFC4601].
When the mAFTR receives the first IPv4 multicast packet, it may extract the multicast source address (S4) from the packet and send an Explicit PIMv4 (S4,G4) Join message directly to S4. The mAFTR will switch from the shared Rendezvous Point Tree (RPT) to the Shortest Path Tree (SPT) for G4.
For IPv6 multicast routers to switch to the SPT, there is no new requirement. IPv6 multicast routers may send an Explicit PIMv6 Join to mAFTR once the first (S6,G6) multicast packet arrives from upstream multicast routers.
When the mAFTR receives an IPv4 multicast packet, it will look up the TIB4 to find a matching entry and then forward the packet to the interface(s) on the outgoing interface list. If the IPv4-in-IPv6 virtual interface also belongs to this list, the packet will be encapsulated with the mPrefix64-derived and uPrefix64-derived IPv4-embedded IPv6 addresses to form an IPv6 multicast packet. Then another lookup is executed to find a matching entry in the TIB6, while whether or not to perform RPF check for the second lookup is up to the implementation and is out of the scope of this document. The IPv6 multicast packet is forwarded along the IPv6 multicast distribution tree, based upon the outgoing interface list of the matching entry in the TIB6.
As an illustration, if a packet is received from source 192.0.2.33 and to be forwarded to group 233.252.0.1, the mAFTR encapsulates it into an IPv6 multicast packet using ff3x:1000::233.252.0.1 as the IPv6 destination address and using 2001:db8::192.0.2.33 as the IPv6 multicast source address.
The Scope field of IPv4-in-IPv6 multicast addresses should be valued accordingly (e.g, to “E”, Global scope;) in the deployment environment. This specification does not discuss the scope value that should be used.
Nevertheless, when several mPrefix64s are available, if each enclosed IPv4-embedded IPv6 multicast prefix has a distinct scope, mAFTR MUST select the appropriate IPv4-embedded IPv6 multicast prefix having a scope matching the IPv4 multicast address used to synthesize an IPv4-embedded IPv6 multicast address.
mAFTR MAY be configured to not preserve the scope when enforcing the address translation algorithm.
A part for multicast scoping considerations (see Section 6.5 and Section 7.5), this document does not introduce any new security concern in addition to what is discussed in Section 5 of [RFC6052], Section 10 of [RFC3810] and Section 6 of [RFC4601].
mB4 SHOULD be provided with appropriate configuration to enable preserving the scope of a multicast message when mapping an IPv4 multicast address into an IPv4-embedded IPv6 multicast address and vice versa.
The CPE that embeds the mB4 function SHOULD be configured to accept incoming MLD messages and traffic forwarded to multicast groups subscribed by receivers located in the customer premises.
The authors would like to thank Dan Wing for his guidance in the early discussions which initiated this work. We also thank Peng Sun, Jie Hu, Qiong Sun, Lizhong Jin, Alain Durand, Dean Cheng, Behcet Sarikaya, Tina Tsou, Rajiv Asati, Xiaohong Deng and S. Venaas for their valuable comments.
This document includes no request to IANA.
| [I-D.ietf-softwire-multicast-prefix-option] | Boucadair, M., Qin, J., Tsou, T. and X. Deng, "DHCPv6 Option for IPv4-Embedded Multicast and Unicast IPv6 Prefixes", Internet-Draft draft-ietf-softwire-multicast-prefix-option-09, August 2015. |
| [RFC2236] | Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, DOI 10.17487/RFC2236, November 1997. |
| [RFC6676] | Venaas, S., Parekh, R., Van de Velde, G., Chown, T. and M. Eubanks, "Multicast Addresses for Documentation", RFC 6676, DOI 10.17487/RFC6676, August 2012. |
| [RFC6890] | Cotton, M., Vegoda, L., Bonica, R. and B. Haberman, "Special-Purpose IP Address Registries", BCP 153, RFC 6890, DOI 10.17487/RFC6890, April 2013. |
IPTV generally includes two categories of service offerings:
Two players intervene in the delivery of this service:
Note that some contract agreements prevent a network provider from altering the content as sent by the content provider for various reasons. Under the contract, multicast streams should be delivered unaltered to the requesting users.
Many current IPTV contents are likely to remain IPv4-formatted and out of control of the network providers. Additionally, there are numerous legacy receivers (e.g., IPv4-only Set Top Boxes (STB)) that can't be upgraded or be easily replaced to support IPv6. As a consequence, IPv4 service continuity MUST be guaranteed during the transition period, including the delivery of multicast services such as Live TV Broadcasting to users.
mAFTR can embed the MLD Querier function (as well as the PIMv6 DR) for optimization. When mB4 sends MLD Report message to this mAFTR, the mAFTR should process the MLD Report message that contain IPv4-embedded IPv6 multicast group subscription information then send the corresponding PIMv4 Join message. (Figure 4)
+---------+
---------| mAFTR |---------
MLD |uPrefix64| PIMv4
|mPreifx64|
+---------+
Figure 4: MLD-PIMv4 Interworking Function
Discussions about the location of the mAFTR capability and related ASM or SSM multicast design considerations are out of the scope of this document.
If mAFTR is the DR of the original IPv4 source, it may simply use the uPrefix64 and mPrefix64 to build the IPv4-embedded IPv6 multicast traffic, the sending of PIMv4 Join message is not necessary.
Given the multiple versions of group membership management protocols, mismatch issues may be raised in the mB4 Function (refer to Section 6.1).
If IGMPv2 operates on the IPv4 receivers while MLDv2 operates on the MLD Querier, or if IGMPv3 operates on the IPv4 receivers while MLDv1 operates on the MLD Querier, the issue mentioned above will be encountered. To solve this problem, the mB4 SHOULD perform the router portion of IGMP which is of the same as the corresponding MLD version (IGMPv2 as of MLDv1, or IGMPv3 as of MLDv2) operating in the IPv6 domain, then the protocol interaction approach specified in Section 7 of [RFC3376] can be used to exchange signaling messages with the IPv4 receivers on which the different version of IGMP is operating.
For robustness and load distribution purposes, several nodes in the network can embed the mAFTR function. In such case, the same IPv6 prefixes (i.e., mPrefix64 and uPrefix64) and algorithm to build IPv4- embedded IPv6 addresses MUST be configured on those nodes.
For the sake of simplicity, it is RECOMMENDED to configure mAFTR as the RP for the IPv4-embedded IPv6 multicast groups it manages. No registration procedure is required under this configuration.
mAFTR may be configured with a list of IPv4 multicast groups and sources. Only multicast flows bound to the configured addresses should be handled by the mAFTR. Otherwise, packets are silently drooped.
To optimize the usage of network resources in current deployments, all multicast streams are conveyed in the core network while only popular ones are continuously conveyed in the aggregation/access network (static mode). Non-popular streams are conveyed in the access network upon request (dynamic mode). Depending on the location of the mAFTR in the network, two modes can be envisaged: static and dynamic.