draft-ietf-softwire-mesh-multicast-13.txt   draft-ietf-softwire-mesh-multicast-14.txt 
Softwire WG M. Xu Softwire WG M. Xu
Internet-Draft Y. Cui Internet-Draft Y. Cui
Intended status: Standards Track J. Wu Intended status: Standards Track J. Wu
Expires: November 23, 2016 S. Yang Expires: May 17, 2017 S. Yang
Tsinghua University Tsinghua University
C. Metz C. Metz
G. Shepherd G. Shepherd
Cisco Systems Cisco Systems
May 22, 2016 November 13, 2016
Softwire Mesh Multicast Softwire Mesh Multicast
draft-ietf-softwire-mesh-multicast-13 draft-ietf-softwire-mesh-multicast-14
Abstract Abstract
The Internet needs to support IPv4 and IPv6 packets. Both address The Internet needs to support IPv4 and IPv6 packets. Both address
families and their related protocol suites support multicast of the families and their related protocol suites support multicast of the
single-source and any-source varieties. During IPv6 transition, single-source and any-source varieties. During IPv6 transition,
there will be scenarios where a backbone network running one IP there will be scenarios where a backbone network running one IP
address family internally (referred to as internal IP or I-IP) will address family internally (referred to as internal IP or I-IP) will
provide transit services to attached client networks running another provide transit services to attached client networks running another
IP address family (referred to as external IP or E-IP). It is IP address family (referred to as external IP or E-IP). It is
expected that the I-IP backbone will offer unicast and multicast expected that the I-IP backbone will offer unicast and multicast
transit services to the client E-IP networks. transit services to the client E-IP networks.
Softwire Mesh is a solution to E-IP unicast and multicast support Softwire Mesh is a solution providing E-IP unicast and multicast
across an I-IP backbone. This document describes the mechanism for support across an I-IP backbone. This document describes the
supporting Internet-style multicast across a set of E-IP and I-IP mechanism for supporting Internet-style multicast across a set of
networks supporting softwire mesh. E-IP and I-IP networks supporting softwire mesh.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 23, 2016. This Internet-Draft will expire on May 17, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3.2. IPv6-over-IPv4 . . . . . . . . . . . . . . . . . . . . . 7 3.2. IPv6-over-IPv4 . . . . . . . . . . . . . . . . . . . . . 7
4. IPv4-over-IPv6 Mechanism . . . . . . . . . . . . . . . . . . 9 4. IPv4-over-IPv6 Mechanism . . . . . . . . . . . . . . . . . . 9
4.1. Mechanism Overview . . . . . . . . . . . . . . . . . . . 9 4.1. Mechanism Overview . . . . . . . . . . . . . . . . . . . 9
4.2. Group Address Mapping . . . . . . . . . . . . . . . . . . 9 4.2. Group Address Mapping . . . . . . . . . . . . . . . . . . 9
4.3. Source Address Mapping . . . . . . . . . . . . . . . . . 10 4.3. Source Address Mapping . . . . . . . . . . . . . . . . . 10
4.4. Routing Mechanism . . . . . . . . . . . . . . . . . . . . 11 4.4. Routing Mechanism . . . . . . . . . . . . . . . . . . . . 11
5. IPv6-over-IPv4 Mechanism . . . . . . . . . . . . . . . . . . 12 5. IPv6-over-IPv4 Mechanism . . . . . . . . . . . . . . . . . . 12
5.1. Mechanism Overview . . . . . . . . . . . . . . . . . . . 12 5.1. Mechanism Overview . . . . . . . . . . . . . . . . . . . 12
5.2. Group Address Mapping . . . . . . . . . . . . . . . . . . 12 5.2. Group Address Mapping . . . . . . . . . . . . . . . . . . 12
5.3. Source Address Mapping . . . . . . . . . . . . . . . . . 12 5.3. Source Address Mapping . . . . . . . . . . . . . . . . . 12
5.4. Routing Mechanism . . . . . . . . . . . . . . . . . . . . 13 5.4. Routing Mechanism . . . . . . . . . . . . . . . . . . . . 14
6. Control Plane Functions of AFBR . . . . . . . . . . . . . . . 14 6. Control Plane Functions of AFBR . . . . . . . . . . . . . . . 14
6.1. E-IP (*,G) State Maintenance . . . . . . . . . . . . . . 14 6.1. E-IP (*,G) State Maintenance . . . . . . . . . . . . . . 14
6.2. E-IP (S,G) State Maintenance . . . . . . . . . . . . . . 14 6.2. E-IP (S,G) State Maintenance . . . . . . . . . . . . . . 14
6.3. I-IP (S',G') State Maintenance . . . . . . . . . . . . . 14 6.3. I-IP (S',G') State Maintenance . . . . . . . . . . . . . 15
6.4. E-IP (S,G,rpt) State Maintenance . . . . . . . . . . . . 15 6.4. E-IP (S,G,rpt) State Maintenance . . . . . . . . . . . . 15
6.5. Inter-AFBR Signaling . . . . . . . . . . . . . . . . . . 15 6.5. Inter-AFBR Signaling . . . . . . . . . . . . . . . . . . 15
6.6. SPT Switchover . . . . . . . . . . . . . . . . . . . . . 17 6.6. SPT Switchover . . . . . . . . . . . . . . . . . . . . . 17
6.7. Other PIM Message Types . . . . . . . . . . . . . . . . . 17 6.7. Other PIM Message Types . . . . . . . . . . . . . . . . . 17
6.8. Other PIM States Maintenance . . . . . . . . . . . . . . 17 6.8. Other PIM States Maintenance . . . . . . . . . . . . . . 17
7. Data Plane Functions of AFBR . . . . . . . . . . . . . . . . 17 7. Data Plane Functions of the AFBR . . . . . . . . . . . . . . 18
7.1. Process and Forward Multicast Data . . . . . . . . . . . 17 7.1. Process and Forward Multicast Data . . . . . . . . . . . 18
7.2. Selecting a Tunneling Technology . . . . . . . . . . . . 18 7.2. Selecting a Tunneling Technology . . . . . . . . . . . . 18
7.3. TTL . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.3. TTL . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.4. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 18 7.4. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 18
8. Packet Format and Translation . . . . . . . . . . . . . . . . 18 8. Packet Format and Translation . . . . . . . . . . . . . . . . 18
9. Softwire Mesh Multicast Encapsulation . . . . . . . . . . . . 19 9. Softwire Mesh Multicast Encapsulation . . . . . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . 20 12.1. Normative References . . . . . . . . . . . . . . . . . . 20
12.2. Informative References . . . . . . . . . . . . . . . . . 21 12.2. Informative References . . . . . . . . . . . . . . . . . 21
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1. Introduction 1. Introduction
The Internet needs to support IPv4 and IPv6 packets. Both address The Internet needs to support IPv4 and IPv6 packets. Both address
families and their related protocol suites support multicast of the families and their related protocol suites support multicast of the
single-source and any-source varieties. During IPv6 transition, single-source and any-source varieties. During IPv6 transition,
there will be scenarios where a backbone network running one IP there will be scenarios where a backbone network running one IP
address family internally (referred to as internal IP or I-IP) will address family internally (referred to as internal IP or I-IP) will
provide transit services to attached client networks running another provide transit services to attached client networks running another
IP address family (referred to as external IP or E-IP). IP address family (referred to as external IP or E-IP).
The preferred solution is to leverage the multicast functions One solution is to leverage the multicast functions inherent in the
inherent in the I-IP backbone, to efficiently forward client E-IP I-IP backbone, to efficiently forward client E-IP multicast packets
multicast packets inside an I-IP core tree, which roots at one or inside an I-IP core tree, which is rooted at one or more ingress AFBR
more ingress AFBR nodes and branches out to one or more egress AFBR nodes and branches out to one or more egress AFBR leaf nodes.
leaf nodes.
[RFC4925] outlines the requirements for the softwires mesh scenario [RFC4925] outlines the requirements for the softwires mesh scenario
including the multicast. It is straightforward to envisage that and includes support for multicast traffic. It is likely that client
client E-IP multicast sources and receivers will reside in different E-IP multicast sources and receivers will reside in different client
client E-IP networks connected to an I-IP backbone network. This E-IP networks connected to an I-IP backbone network. This requires
requires that the client E-IP source-rooted or shared tree should the client E-IP source-rooted or shared tree to traverse the I-IP
traverse the I-IP backbone network. backbone network.
One method to accomplish this is to re-use the multicast VPN approach One method of accomplishing this is to re-use the multicast VPN
outlined in [RFC6513]. MVPN-like schemes can support the softwire approach outlined in [RFC6513]. MVPN-like schemes can support the
mesh scenario and achieve a "many-to-one" mapping between the E-IP softwire mesh scenario and achieve a "many-to-one" mapping between
client multicast trees and the transit core multicast trees. The the E-IP client multicast trees and the transit core multicast trees.
advantage of this approach is that the number of trees in the I-IP The advantage of this approach is that the number of trees in the
backbone network scales less than linearly with the number of E-IP I-IP backbone network scales less than linearly with the number of
client trees. Corporate enterprise networks and by extension E-IP client trees. Corporate enterprise networks and by extension
multicast VPNs have been known to run applications that create too multicast VPNs have been known to run applications that create too
many (S,G) states. Aggregation at the edge contains the (S,G) states many (S,G) states. Aggregation at the edge contains the (S,G) states
that need to be maintained by the network operator supporting the for customer's VPNs and these need to be maintained by the network
customer VPNs. The disadvantage of this approach is the possible operator. The disadvantage of this approach is the possibility of
inefficient bandwidth and resource utilization when multicast packets inefficient bandwidth and resource utilization when multicast packets
are delivered to a receiver AFBR with no attached E-IP receivers. are delivered to a receiving AFBR with no attached E-IP receivers.
Internet-style multicast is somewhat different in that the trees are Internet-style multicast is somewhat different in that the trees are
relatively sparse and source-rooted. The need for multicast source-rooted and relatively sparse. The need for multicast
aggregation at the edge (where many customer multicast trees are aggregation at the edge (where many customer multicast trees are
mapped into a few or one backbone multicast trees) does not exist and mapped into one or more backbone multicast trees) does not exist and
to date has not been identified. Thus the need for a basic or closer to date has not been identified. Thus the need for a basic or closer
alignment with E-IP and I-IP multicast procedures emerges. alignment with E-IP and I-IP multicast procedures emerges.
A framework on how to support such methods is described in [RFC5565]. [RFC5565] describes the "Softwire Mesh Framework". This document
In this document, a more detailed discussion supporting the "one-to- provides a more detailed description of how one-to-one mapping
one" mapping schemes for the IPv6 over IPv4 and IPv4 over IPv6 schemes ([RFC5565], Section 11.1) for IPv6 over IPv4 and IPv4 over
scenarios will be discussed. IPv6 can be achieved.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Terminology 2. Terminology
An example of a softwire mesh network supporting multicast is Figure 1 shows an example of how a softwire mesh network can support
illustrated in Figure 1. A multicast source S is located in one E-IP multicast traffic. A multicast source S is located in one E-IP
client network, while candidate E-IP group receivers are located in client network, while candidate E-IP group receivers are located in
the same or different E-IP client networks that all share a common the same or different E-IP client networks that all share a common
I-IP transit network. When E-IP sources and receivers are not local I-IP transit network. When E-IP sources and receivers are not local
to each other, they can only communicate with each other through the to each other, they can only communicate with each other through the
I-IP core. There may be several E-IP sources for some multicast I-IP core. There may be several E-IP sources for a single multicast
group residing in different client E-IP networks. In the case of group residing in different client E-IP networks. In the case of
shared trees, the E-IP sources, receivers and RPs might be located in shared trees, the E-IP sources, receivers and RPs might be located in
different client E-IP networks. In a simple case the resources of different client E-IP networks. In the simplest case, a single
the I-IP core are managed by a single operator although the inter- operator manages the resources of the I-IP core, although the inter-
provider case is not precluded. operator case is also possible and so not precluded.
._._._._. ._._._._. ._._._._. ._._._._.
| | | | -------- | | | | --------
| E-IP | | E-IP |--|Source S| | E-IP | | E-IP |--|Source S|
| network | | network | -------- | network | | network | --------
._._._._. ._._._._. ._._._._. ._._._._.
| | | |
AFBR upstream AFBR AFBR upstream AFBR
| | | |
__+____________________+__ __+____________________+__
/ : : : : \ / : : : : \
| : : : : | E-IP Multicast | : : : : | E-IP Multicast
| : I-IP transit core : | packets MUST | : I-IP transit core : | packets are forwarded
| : : : : | get across the | : : : : | across the I-IP
| : : : : | I-IP transit core | : : : : | transit core
\_._._._._._._._._._._._._./ \_._._._._._._._._._._._._./
+ + + +
downstream AFBR downstream AFBR downstream AFBR downstream AFBR
| | | |
._._._._ ._._._._ ._._._._ ._._._._
-------- | | | | -------- -------- | | | | --------
|Receiver|-- | E-IP | | E-IP |--|Receiver| |Receiver|-- | E-IP | | E-IP |--|Receiver|
-------- |network | |network | -------- -------- |network | |network | --------
._._._._ ._._._._ ._._._._ ._._._._
Figure 1: Softwire Mesh Multicast Framework Figure 1: Softwire Mesh Multicast Framework
Terminologies used in this document: Terminology used in this document:
o Address Family Border Router (AFBR) - A router interconnecting two o Address Family Border Router (AFBR) - A router interconnecting two
or more networks using different IP address families. In the context or more networks using different IP address families. In the context
of softwire mesh multicast, the AFBR runs E-IP and I-IP control of softwire mesh multicast, the AFBR runs E-IP and I-IP control
planes to maintain E-IP and I-IP multicast states respectively and planes to maintain E-IP and I-IP multicast states respectively and
performs the appropriate encapsulation/decapsulation of client E-IP performs the appropriate encapsulation/decapsulation of client E-IP
multicast packets for transport across the I-IP core. An AFBR will multicast packets for transport across the I-IP core. An AFBR will
act as a source and/or receiver in an I-IP multicast tree. act as a source and/or receiver in an I-IP multicast tree.
o Upstream AFBR: The AFBR router that is located on the upper reaches o Upstream AFBR: The AFBR router that is located on the upper reaches
of a multicast data flow. of a multicast data flow.
o Downstream AFBR: The AFBR router that is located on the lower o Downstream AFBR: The AFBR router that is located on the lower
reaches of a multicast data flow. reaches of a multicast data flow.
o I-IP (Internal IP): This refers to the form of IP (i.e., either o I-IP (Internal IP): This refers to IP address family (i.e., either
IPv4 or IPv6) that is supported by the core (or backbone) network. IPv4 or IPv6) that is supported by the core (or backbone) network.
An I-IPv6 core network runs IPv6 and an I-IPv4 core network runs An I-IPv6 core network runs IPv6 and an I-IPv4 core network runs
IPv4. IPv4.
o E-IP (External IP): This refers to the form of IP (i.e. either IPv4 o E-IP (External IP): This refers to the IP address family (i.e.
or IPv6) that is supported by the client network(s) attached to the either IPv4 or IPv6) that is supported by the client network(s)
I-IP transit core. An E-IPv6 client network runs IPv6 and an E-IPv4 attached to the I-IP transit core. An E-IPv6 client network runs
client network runs IPv4. IPv6 and an E-IPv4 client network runs IPv4.
o I-IP core tree: A distribution tree rooted at one or more AFBR o I-IP core tree: A distribution tree rooted at one or more AFBR
source nodes and branched out to one or more AFBR leaf nodes. An source nodes and branched out to one or more AFBR leaf nodes. An
I-IP core tree is built using standard IP or MPLS multicast signaling I-IP core tree is built using standard IP or MPLS multicast signaling
protocols operating exclusively inside the I-IP core network. An protocols operating exclusively inside the I-IP core network. An
I-IP core tree is used to forward E-IP multicast packets belonging to I-IP core tree is used to forward E-IP multicast packets belonging to
E-IP trees across the I-IP core. Another name for an I-IP core tree E-IP trees across the I-IP core. Another name for an I-IP core tree
is multicast or multipoint softwire. is multicast or multipoint softwire.
o E-IP client tree: A distribution tree rooted at one or more hosts o E-IP client tree: A distribution tree rooted at one or more hosts
or routers located inside a client E-IP network and branched out to or routers located inside a client E-IP network and branched out to
one or more leaf nodes located in the same or different client E-IP one or more leaf nodes located in the same or different client E-IP
networks. networks.
o uPrefix64: The /96 unicast IPv6 prefix for constructing o uPrefix64: The /96 unicast IPv6 prefix for constructing an
IPv4-embedded IPv6 source address in IPv6-over-IPv4 scenario. IPv4-embedded IPv6 source address in IPv6-over-IPv4 scenario.
o uPrefix46: The /96 unicast IPv6 prefix for constructing o uPrefix46: The /96 unicast IPv6 prefix for constructing an
IPv4-embedded IPv6 source address in IPv4-over-IPv6 scenario. IPv4-embedded IPv6 source address in IPv4-over-IPv6 scenario.
o mPrefix46: The /96 multicast IPv6 prefix for constructing o mPrefix46: The /96 multicast IPv6 prefix for constructing an
IPv4-embedded IPv6 multicast address in IPv4-over-IPv6 scenario. IPv4-embedded IPv6 multicast address in IPv4-over-IPv6 scenario.
o Inter-AFBR signaling: A mechanism used by downstream AFBRs to send o Inter-AFBR signaling: A mechanism used by downstream AFBRs to send
PIM messages to the upstream AFBR. PIM messages to the upstream AFBR.
3. Scenarios of Interest 3. Scenarios of Interest
This section describes the two different scenarios where softwires This section describes the two different scenarios that softwires
mesh multicast will apply. mesh multicast is appliacable to.
3.1. IPv4-over-IPv6 3.1. IPv4-over-IPv6
._._._._. ._._._._. ._._._._. ._._._._.
| IPv4 | | IPv4 | -------- | IPv4 | | IPv4 | --------
| Client | | Client |--|Source S| | Client | | Client |--|Source S|
| network | | network | -------- | network | | network | --------
._._._._. ._._._._. ._._._._. ._._._._.
| | | |
AFBR upstream AFBR AFBR upstream AFBR
| | | |
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downstream AFBR downstream AFBR downstream AFBR downstream AFBR
| | | |
._._._._ ._._._._ ._._._._ ._._._._
-------- | IPv4 | | IPv4 | -------- -------- | IPv4 | | IPv4 | --------
|Receiver|-- | Client | | Client |--|Receiver| |Receiver|-- | Client | | Client |--|Receiver|
-------- | network| | network| -------- -------- | network| | network| --------
._._._._ ._._._._ ._._._._ ._._._._
Figure 2: IPv4-over-IPv6 Scenario Figure 2: IPv4-over-IPv6 Scenario
In this scenario, the E-IP client networks run IPv4 and I-IP core In Figure 2, the E-IP client networks run IPv4 and the I-IP core runs
runs IPv6. This scenario is illustrated in Figure 2. IPv6.
Because of the much larger IPv6 group address space, it will not be a Because of the much larger IPv6 group address space, the client
problem to map individual client E-IPv4 tree to a specific I-IPv6 E-IPv4 tree can be mapped to a specific I-IPv6 core tree. This
core tree. This simplifies operations on the AFBR because it becomes simplifies operations on the AFBR because it becomes possible to
possible to algorithmically map an IPv4 group/source address to an algorithmically map an IPv4 group/source address to an IPv6 group/
IPv6 group/source address and vice-versa. source address and vice-versa.
The IPv4-over-IPv6 scenario is an emerging requirement as network The IPv4-over-IPv6 scenario is an emerging requirement as network
operators build out native IPv6 backbone networks. These networks operators build out native IPv6 backbone networks. These networks
naturally support native IPv6 services and applications but it is support native IPv6 services and applications but in many cases,
with near 100% certainty that legacy IPv4 networks handling unicast support for legacy IPv4 unicast and multicast services will also need
and multicast MUST be accommodated. to be accomodated.
3.2. IPv6-over-IPv4 3.2. IPv6-over-IPv4
._._._._. ._._._._. ._._._._. ._._._._.
| IPv6 | | IPv6 | -------- | IPv6 | | IPv6 | --------
| Client | | Client |--|Source S| | Client | | Client |--|Source S|
| network | | network | -------- | network | | network | --------
._._._._. ._._._._. ._._._._. ._._._._.
| | | |
AFBR upstream AFBR AFBR upstream AFBR
| | | |
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downstream AFBR downstream AFBR downstream AFBR downstream AFBR
| | | |
._._._._ ._._._._ ._._._._ ._._._._
-------- | IPv6 | | IPv6 | -------- -------- | IPv6 | | IPv6 | --------
|Receiver|-- | Client | | Client |--|Receiver| |Receiver|-- | Client | | Client |--|Receiver|
-------- | network| | network| -------- -------- | network| | network| --------
._._._._ ._._._._ ._._._._ ._._._._
Figure 3: IPv6-over-IPv4 Scenario Figure 3: IPv6-over-IPv4 Scenario
In this scenario, the E-IP Client Networks run IPv6 while the I-IP In Figure 3, the E-IP Client Networks run IPv6 while the I-IP core
core runs IPv4. This scenario is illustrated in Figure 3. runs IPv4.
IPv6 multicast group addresses are longer than IPv4 multicast group IPv6 multicast group addresses are longer than IPv4 multicast group
addresses. It will not be possible to perform an algorithmic IPv6 - addresses so it is not possible to perform an algorithmic IPv6 to
to - IPv4 address mapping without the risk of multiple IPv6 group IPv4 address mapping without the risk of multiple IPv6 group
addresses mapped to the same IPv4 address resulting in unnecessary addresses mapped to the same IPv4 address, resulting in unnecessary
bandwidth and resource consumption. Therefore additional efforts bandwidth and resource consumption.Therefore, additional efforts will
will be REQUIRED to ensure that client E-IPv6 multicast packets can be required to ensure that client E-IPv6 multicast packets can be
be injected into the correct I-IPv4 multicast trees at the AFBRs. injected into the correct I-IPv4 multicast trees at the AFBRs. This
This clear mismatch in IPv6 and IPv4 group address lengths means that clear mismatch in IPv6 and IPv4 group address lengths means that it
it will not be possible to perform a one-to-one mapping between IPv6 will not be possible to perform a one-to-one mapping between IPv6 and
and IPv4 group addresses unless the IPv6 group address is scoped. IPv4 group addresses unless the IPv6 group address is scoped, such as
applying a "Well-Known" prefix or an ISP-defined prefix.
As mentioned earlier, this scenario is common in the MVPN As mentioned earlier, this scenario is common in the MVPN
environment. As native IPv6 deployments and multicast applications environment. As native IPv6 deployments and multicast applications
emerge from the outer reaches of the greater public IPv4 Internet, it emerge from the outer reaches of the greater public IPv4 Internet, it
is envisaged that the IPv6 over IPv4 softwire mesh multicast scenario is envisaged that the IPv6 over IPv4 softwire mesh multicast scenario
will be a necessary feature supported by network operators. will be a necessary feature supported by network operators.
4. IPv4-over-IPv6 Mechanism 4. IPv4-over-IPv6 Mechanism
4.1. Mechanism Overview 4.1. Mechanism Overview
Routers in the client E-IPv4 networks contain routes to all other Routers in the client E-IPv4 networks have routes to all other client
client E-IPv4 networks. Through the set of known and deployed E-IPv4 networks. Through PIM messages, E-IPv4 hosts and routers have
mechanisms, E-IPv4 hosts and routers have discovered or learnt of discovered or learnt of (S,G) or (*,G) IPv4 addresses. Any I-IPv6
(S,G) or (*,G) IPv4 addresses. Any I-IPv6 multicast state multicast state instantiated in the core is referred to as (S',G') or
instantiated in the core is referred to as (S',G') or (*,G') and is (*,G') and is certainly separated from E-IPv4 multicast state.
certainly separated from E-IPv4 multicast state.
Suppose a downstream AFBR receives an E-IPv4 PIM Join/Prune message Suppose a downstream AFBR receives an E-IPv4 PIM Join/Prune message
from the E-IPv4 network for either an (S,G) tree or a (*,G) tree. from the E-IPv4 network for either an (S,G) tree or a (*,G) tree.
The AFBR can translate the E-IPv4 PIM message into an I-IPv6 PIM The AFBR can translate the E-IPv4 PIM message into an I-IPv6 PIM
message with the latter being directed towards I-IP IPv6 address of message with the latter being directed towards the I-IP IPv6 address
the upstream AFBR. When the I-IPv6 PIM message arrives at the of the upstream AFBR. When the I-IPv6 PIM message arrives at the
upstream AFBR, it MUST be translated back into an E-IPv4 PIM message. upstream AFBR, it MUST be translated back into an E-IPv4 PIM message.
The result of these actions is the construction of E-IPv4 trees and a The result of these actions is the construction of E-IPv4 trees and a
corresponding I-IP tree in the I-IP network. corresponding I-IP tree in the I-IP network. An example of the
packet format and traslation is provided in Section 8.
In this case, it is incumbent upon the AFBR routers to perform PIM In this case, it is incumbent upon the AFBR routers to perform PIM
message conversions in the control plane and IP group address message conversions in the control plane and IP group address
conversions or mappings in the data plane. It becomes possible to conversions or mappings in the data plane. The AFBRs perform an
devise an algorithmic one-to-one IPv4-to-IPv6 address mapping at algorithmic, one-to-one mapping of IPv4-to-IPv6.
AFBRs.
4.2. Group Address Mapping 4.2. Group Address Mapping
For IPv4-over-IPv6 scenario, a simple algorithmic mapping between For the IPv4-over-IPv6 scenario, a simple algorithmic mapping between
IPv4 multicast group addresses and IPv6 group addresses is supported. IPv4 multicast group addresses and IPv6 group addresses is performed.
[RFC7371] has already defined an applicable format. Figure 4 is the Figure 4 shows the reminder of the format:
reminder of the format:
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0-------------32--40--48--56--64--72--80--88--96-----------127| | 0-------------32--40--48--56--64--72--80--88--96-----------127|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| mPrefix46 |group address | | mPrefix46 |group address |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 4: IPv4-Embedded IPv6 Multicast Address Format Figure 4: IPv4-Embedded IPv6 Multicast Address Format
The mPrefix46 for SSM mode is also defined in Section 4.1 of An IPv6 multicast prefix (mPrefix46) is assigned to each AFBR. AFBRs
[RFC7371] : will prepend the prefix to an IPv4 multicast group address when
translating it to an IPv6 multicast group address.
o ff3x:0:8000::/96 ('x' is any valid scope) The mPrefix46 for SSM mode is also defined in Section 4.1 of
[RFC7371]
With this scheme, each IPv4 multicast address can be mapped into an With this scheme, each IPv4 multicast address can be mapped into an
IPv6 multicast address (with the assigned prefix), and each IPv6 IPv6 multicast address (with the assigned prefix), and each IPv6
multicast address with the assigned prefix can be mapped into IPv4 multicast address with the assigned prefix can be mapped into an IPv4
multicast address. multicast address.
4.3. Source Address Mapping 4.3. Source Address Mapping
There are two kinds of multicast --- ASM and SSM. Considering that There are two kinds of multicast: ASM and SSM. Considering that I-IP
I-IP network and E-IP network may support different kind of network and E-IP network may support different kinds of multicast,
multicast, the source address translation rules could be very complex the source address translation rules needed to support all possible
to support all possible scenarios. But since SSM can be implemented scenarios may become very complex. But since SSM can be implemented
with a strict subset of the PIM-SM protocol mechanisms [RFC7761], we with a strict subset of the PIM-SM protocol mechanisms [RFC7761], we
can treat I-IP core as SSM-only to make it as simple as possible, can treat the I-IP core as SSM-only to make it as simple as possible.
then there remains only two scenarios to be discussed in detail: There then remain only two scenarios to be discussed in detail:
o E-IP network supports SSM o E-IP network supports SSM
One possible way to make sure that the translated I-IPv6 PIM One possible way to make sure that the translated I-IPv6 PIM
message reaches upstream AFBR is to set S' to a virtual IPv6 message reaches upstream AFBR is to set S' to a virtual IPv6
address that leads to the upstream AFBR. Figure 5 is the address that leads to the upstream AFBR. Figure 5 is the
recommended address format based on [RFC6052]: recommended address format based on [RFC6052]:
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0-------------32--40--48--56--64--72--80--88--96-----------127| | 0-------------32--40--48--56--64--72--80--88--96-----------127|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| prefix |v4(32) | u | suffix |source address | | prefix |v4(32) | u | suffix |source address |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|<------------------uPrefix46------------------>| |<------------------uPrefix46------------------>|
Figure 5: IPv4-Embedded IPv6 Virtual Source Address Format Figure 5: IPv4-Embedded IPv6 Virtual Source Address Format
In this address format, the "prefix" field contains a "Well-Known" In this address format,
prefix or an ISP-defined prefix. An existing "Well-Known" prefix
is 64:ff9b, which is defined in [RFC6052]; "v4" field is the IP * The "prefix" field contains a "Well-Known" prefix or an ISP-
address of one of upstream AFBR's E-IPv4 interfaces; "u" field is defined prefix. An existing "Well-Known" prefix is 64:ff9b,
defined in [RFC4291], and MUST be set to zero; "suffix" field is which is defined in [RFC6052];
reserved for future extensions and SHOULD be set to zero; "source
address" field stores the original S. We call the overall /96 * The "v4" field is the IP address of one of upstream AFBR's
prefix ("prefix" field and "v4" field and "u" field and "suffix" E-IPv4 interfaces;
field altogether) "uPrefix46".
* The "u" field is defined in [RFC4291], and MUST be set to zero;
* The "suffix" field is reserved for future extensions and SHOULD
be set to zero;
* The "source address" field stores the original S.
We call the overall /96 prefix ("prefix" field and "v4" field and
"u" field and "suffix" field altogether) "uPrefix46".
o E-IP network supports ASM o E-IP network supports ASM
The (S,G) source list entry and the (*,G) source list entry only The (S,G) source list entry and the (*,G) source list entry only
differ in that the latter has both the WC and RPT bits of the differ in that the latter has both the WC and RPT bits of the
Encoded-Source-Address set, while the former is all cleared (See Encoded-Source-Address set, while the former is all cleared (See
Section 4.9.5.1 of [RFC7761]). So we can translate source list Section 4.9.5.1 of [RFC7761]). So we can translate source list
entries in (*,G) messages into source list entries in (S'G') entries in (*,G) messages into source list entries in (S'G')
messages by applying the format specified in Figure 5 and clearing messages by applying the format specified in Figure 5 and clearing
both the WC and RPT bits at downstream AFBRs, and translate them both the WC and RPT bits at downstream AFBRs, and vice-versa for
back at upstream AFBRs vice-versa. the reverse translation at upstream AFBRs.
4.4. Routing Mechanism 4.4. Routing Mechanism
In the mesh multicast scenario, routing information is REQUIRED to be In the mesh multicast scenario, routing information is REQUIRED to be
distributed among AFBRs to make sure that PIM messages that a distributed among AFBRs to make sure that the PIM messages that a
downstream AFBR propagates reach the right upstream AFBR. downstream AFBR propagates reach the right upstream AFBR.
To make it feasible, the /32 prefix in "IPv4-Embedded IPv6 Virtual Every AFBR MUST know the /32 prefix in "IPv4-Embedded IPv6 Virtual
Source Address Format" MUST be known to every AFBR, and every AFBR Source Address Format". To achieve this, every AFBR should announce
should not only announce the IP address of one of its E-IPv4 one of its E-IPv4 interfaces in the "v4" field, and the corresponding
interfaces presented in the "v4" field to other AFBRs by MPBGP, but uPrefix46. The announcement SHOULD be sent to the other AFBRs
also announce the corresponding uPrefix46 to the I-IPv6 network. through MBGP. Since every IP address of upstream AFBR's E-IPv4
Since every IP address of upstream AFBR's E-IPv4 interface is interface is different from each other, every uPrefix46 that AFBR
different from each other, every uPrefix46 that AFBR announces MUST announces MUST be different, and uniquely identifies each AFBR.
be different, and uniquely identifies each AFBR. "uPrefix46" is an "uPrefix46" is an IPv6 prefix, and the distribution mechanism is the
IPv6 prefix, and the distribution of it is the same as the same as the traditional mesh unicast scenario. But "v4" field is an
distribution in the traditional mesh unicast scenario. But since E-IPv4 address, and BGP messages are NOT tunneled through softwires
"v4" field is an E-IPv4 address, and BGP messages are NOT tunneled or any other mechanism specified in [RFC5565], AFBRs MUST be able to
through softwires or through any other mechanism as specified in transport and encode/decode BGP messages that are carried over
[RFC5565], AFBRs MUST be able to transport and encode/decode BGP I-IPv6, whose NLRI and NH are of E-IPv4 address family.
messages that are carried over I-IPv6, whose NLRI and NH are of
E-IPv4 address family.
In this way, when a downstream AFBR receives an E-IPv4 PIM (S,G) In this way, when a downstream AFBR receives an E-IPv4 PIM (S,G)
message, it can translate this message into (S',G') by looking up the message, it can translate this message into (S',G') by looking up the
IP address of the corresponding AFBR's E-IPv4 interface. Since the IP address of the corresponding AFBR's E-IPv4 interface. Since the
uPrefix46 of S' is unique, and is known to every router in the I-IPv6 uPrefix46 of S' is unique, and is known to every router in the I-IPv6
network, the translated message will eventually arrive at the network, the translated message will be forwarded to the
corresponding upstream AFBR, and the upstream AFBR can translate the corresponding upstream AFBR, and the upstream AFBR can translate the
message back to (S,G). When a downstream AFBR receives an E-IPv4 PIM message back to (S,G). When a downstream AFBR receives an E-IPv4 PIM
(*,G) message, S' can be generated according to the format specified (*,G) message, S' can be generated according to the format specified
in Figure 4, with "source address" field set to *(the IPv4 address of in Figure 4, with "source address" field set to *(the IPv4 address of
RP). The translated message will eventually arrive at the RP). The translated message will be forwarded to the corresponding
corresponding upstream AFBR. Since every PIM router within a PIM upstream AFBR. Since every PIM router within a PIM domain MUST be
domain MUST be able to map a particular multicast group address to able to map a particular multicast group address to the same RP (see
the same RP (see Section 4.7 of [RFC7761]), when this upstream AFBR Section 4.7 of [RFC7761]), when the upstream AFBR checks the "source
checks the "source address" field of the message, it will find the address" field of the message, it finds the IPv4 address of the RP,
IPv4 address of RP, so this upstream AFBR judges that this is and assertains that this is originally a (*,G) message. This is then
originally a (*,G) message, then it translates the message back to translated back to the (*,G) message and processed.
the (*,G) message and processes it.
5. IPv6-over-IPv4 Mechanism 5. IPv6-over-IPv4 Mechanism
5.1. Mechanism Overview 5.1. Mechanism Overview
Routers in the client E-IPv6 networks contain routes to all other Routers in the client E-IPv6 networks contain routes to all other
client E-IPv6 networks. Through the set of known and deployed client E-IPv6 networks. Through PIM messages, E-IPv6 hosts and
mechanisms, E-IPv6 hosts and routers have discovered or learnt of routers have discovered or learnt of (S,G) or (*,G) IPv6 addresses.
(S,G) or (*,G) IPv6 addresses. Any I-IP multicast state instantiated Any I-IP multicast state instantiated in the core is referred to as
in the core is referred to as (S',G') or (*,G') and is certainly (S',G') or (*,G') and is separated from E-IP multicast state.
separated from E-IP multicast state.
This particular scenario introduces unique challenges. Unlike the This particular scenario introduces unique challenges. Unlike the
IPv4-over-IPv6 scenario, it is impossible to map all of the IPv6 IPv4-over-IPv6 scenario, it is impossible to map all of the IPv6
multicast address space into the IPv4 address space to address the multicast address space into the IPv4 address space to address the
one-to-one Softwire Multicast requirement. To coordinate with the one-to-one Softwire Multicast requirement. To coordinate with the
"IPv4-over-IPv6" scenario and keep the solution as simple as "IPv4-over-IPv6" scenario and keep the solution as simple as
possible, one possible solution to this problem is to limit the scope possible, one possible solution to this problem is to limit the scope
of the E-IPv6 source addresses for mapping, such as applying a "Well- of the E-IPv6 source addresses for mapping, such as applying a "Well-
Known" prefix or an ISP-defined prefix. Known" prefix or an ISP-defined prefix.
5.2. Group Address Mapping 5.2. Group Address Mapping
To keep one-to-one group address mapping simple, the group address To keep one-to-one group address mapping simple, the group address
range of E-IP IPv6 can be reduced in a number of ways to limit the range of E-IP IPv6 can be reduced in a number of ways to limit the
scope of addresses that need to be mapped into the I-IP IPv4 space. scope of addresses that need to be mapped into the I-IP IPv4 space.
A recommended multicast address format is defined in [RFC7371]. The For example, the high order bits of the E-IPv6 address range will be
high order bits of the E-IPv6 address range will be fixed for mapping fixed for mapping purposes. With this scheme, each IPv4 multicast
purposes. With this scheme, each IPv4 multicast address can be address can be mapped into an IPv6 multicast address (with the
mapped into an IPv6 multicast address (with the assigned prefix), and assigned prefix), and each IPv6 multicast address with the assigned
each IPv6 multicast address with the assigned prefix can be mapped prefix can be mapped into an IPv4 multicast address.
into IPv4 multicast address.
5.3. Source Address Mapping 5.3. Source Address Mapping
There are two kinds of multicast --- ASM and SSM. Considering that There are two kinds of multicast --- ASM and SSM. Considering that
I-IP network and E-IP network may support different kind of I-IP network and E-IP network may support different kind of
multicast, the source address translation rules could be very complex multicast, the source address translation rules needed to support all
to support all possible scenarios. But since SSM can be implemented possible scenarios may become very complex. But since SSM can be
with a strict subset of the PIM-SM protocol mechanisms [RFC7761], we implemented with a strict subset of the PIM-SM protocol mechanisms
can treat I-IP core as SSM-only to make it as simple as possible, [RFC7761], we can treat the I-IP core as SSM-only to make it as
then there remains only two scenarios to be discussed in detail: simple as possible. There then remain only two scenarios to be
discussed in detail:
o E-IP network supports SSM o E-IP network supports SSM
To make sure that the translated I-IPv4 PIM message reaches the To make sure that the translated I-IPv4 PIM message reaches the
upstream AFBR, we need to set S' to an IPv4 address that leads to upstream AFBR, we need to set S' to an IPv4 address that leads to
the upstream AFBR. But due to the non-"one-to-one" mapping of the upstream AFBR. But due to the non-"one-to-one" mapping of
E-IPv6 to I-IPv4 unicast address, the upstream AFBR is unable to E-IPv6 to I-IPv4 unicast address, the upstream AFBR is unable to
remap the I-IPv4 source address to the original E-IPv6 source remap the I-IPv4 source address to the original E-IPv6 source
address without any constraints. address without any constraints.
We apply a fixed IPv6 prefix and static mapping to solve this We apply a fixed IPv6 prefix and static mapping to solve this
problem. A recommended source address format is defined in problem. A recommended source address format is defined in
[RFC6052]. Figure 6 is the reminder of the format: [RFC6052]. Figure 6 is the reminder of the format:
skipping to change at page 13, line 25 skipping to change at page 13, line 30
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0-------------32--40--48--56--64--72--80--88--96-----------127| | 0-------------32--40--48--56--64--72--80--88--96-----------127|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| uPrefix64 |source address | | uPrefix64 |source address |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 6: IPv4-Embedded IPv6 Source Address Format Figure 6: IPv4-Embedded IPv6 Source Address Format
In this address format, the "uPrefix64" field starts with a "Well- In this address format, the "uPrefix64" field starts with a "Well-
Known" prefix or an ISP-defined prefix. An existing "Well-Known" Known" prefix or an ISP-defined prefix. An existing "Well-Known"
prefix is 64:ff9b/32, which is defined in [RFC6052]; "source prefix is 64:ff9b/32, which is defined in [RFC6052]; The "source
address" field is the corresponding I-IPv4 source address. address" field is the corresponding I-IPv4 source address.
o E-IP network supports ASM o The E-IP network supports ASM
The (S,G) source list entry and the (*,G) source list entry only The (S,G) source list entry and the (*,G) source list entry only
differ in that the latter has both the WC and RPT bits of the differ in that the latter has both the WC and RPT bits of the
Encoded-Source-Address set, while the former is all cleared (See Encoded-Source-Address set, while the former is all cleared (See
Section 4.9.5.1 of [RFC7761]). So we can translate source list Section 4.9.5.1 of [RFC7761]). So we can translate source list
entries in (*,G) messages into source list entries in (S',G') entries in (*,G) messages into source list entries in (S',G')
messages by applying the format specified in Figure 5 and setting messages by applying the format specified in Figure 5 and setting
both the WC and RPT bits at downstream AFBRs, and translate them both the WC and RPT bits at downstream AFBRs, and vice-versa for
back at upstream AFBRs vice-versa. Here, the E-IPv6 address of RP the reverse translation at upstream AFBRs. Here, the E-IPv6
MUST follow the format specified in Figure 6. RP' is the upstream address of RP MUST follow the format specified in Figure 6. RP'
AFBR that locates between RP and the downstream AFBR. is the upstream AFBR that locates between RP and the downstream
AFBR.
5.4. Routing Mechanism 5.4. Routing Mechanism
In the mesh multicast scenario, routing information is REQUIRED to be In the mesh multicast scenario, routing information is REQUIRED to be
distributed among AFBRs to make sure that PIM messages that a distributed among AFBRs to make sure that PIM messages that a
downstream AFBR propagates reach the right upstream AFBR. downstream AFBR propagates reach the right upstream AFBR.
To make it feasible, the /96 uPrefix64 MUST be known to every AFBR, To make it feasible, the /96 uPrefix64 MUST be known to every AFBR,
every E-IPv6 address of sources that support mesh multicast MUST every E-IPv6 address of sources that support mesh multicast MUST
follow the format specified in Figure 6, and the corresponding follow the format specified in Figure 6, and the corresponding
upstream AFBR of this source MUST announce the I-IPv4 address in upstream AFBR of this source MUST announce the I-IPv4 address in
"source address" field of this source's IPv6 address to the I-IPv4 "source address" field of this source's IPv6 address to the I-IPv4
network. Since uPrefix64 is static and unique in IPv6-over-IPv4 network. Since uPrefix64 is static and unique in IPv6-over-IPv4
scenario, there is no need to distribute it using BGP. The scenario, there is no need to distribute it using BGP. The
distribution of "source address" field of multicast source addresses distribution of "source address" field of multicast source addresses
is a pure I-IPv4 process and no more specification is needed. is a pure I-IPv4 process and no more specification is needed.
In this way, when a downstream AFBR receives a (S,G) message, it can In this way, when a downstream AFBR receives a (S,G) message, it can
translate the message into (S',G') by simply taking off the prefix in translate the message into (S',G') by simply taking off the prefix in
S. Since S' is known to every router in I-IPv4 network, the S. Since S' is known to every router in I-IPv4 network, the
translated message will eventually arrive at the corresponding translated message will be forwarded to the corresponding upstream
upstream AFBR, and the upstream AFBR can translate the message back AFBR, and the upstream AFBR can translate the message back to (S,G)
to (S,G) by appending the prefix to S'. When a downstream AFBR by appending the prefix to S'. When a downstream AFBR receives a
receives a (*,G) message, it can translate it into (S',G') by simply (*,G) message, it can translate it into (S',G') by simply taking off
taking off the prefix in *(the E-IPv6 address of RP). Since S' is the prefix in *(the E-IPv6 address of RP). Since S' is known to
known to every router in I-IPv4 network, the translated message will every router in I-IPv4 network, the translated message will be
eventually arrive at RP'. And since every PIM router within a PIM forwarded to RP'. And since every PIM router within a PIM domain
domain MUST be able to map a particular multicast group address to MUST be able to map a particular multicast group address to the same
the same RP (see Section 4.7 of [RFC7761]), RP' knows that S' is the RP (see Section 4.7 of [RFC7761]), RP' knows that S' is the mapped
mapped I-IPv4 address of RP, so RP' will translate the message back I-IPv4 address of RP, so RP' will translate the message back to (*,G)
to (*,G) by appending the prefix to S' and propagate it towards RP. by appending the prefix to S' and propagate it towards RP.
6. Control Plane Functions of AFBR 6. Control Plane Functions of AFBR
The AFBRs are responsible for the following functions: AFBRs are responsible for the following functions:
6.1. E-IP (*,G) State Maintenance 6.1. E-IP (*,G) State Maintenance
When an AFBR wishes to propagate a Join/Prune(*,G) message to an I-IP When an AFBR wishes to propagate a Join/Prune(*,G) message to an I-IP
upstream router, the AFBR MUST translate Join/Prune(*,G) messages upstream router, the AFBR MUST translate Join/Prune(*,G) messages
into Join/Prune(S',G') messages following the rules specified above, into Join/Prune(S',G') messages following the rules specified above,
then send the latter. then send the latter.
6.2. E-IP (S,G) State Maintenance 6.2. E-IP (S,G) State Maintenance
When an AFBR wishes to propagate a Join/Prune(S,G) message to an I-IP When an AFBR wishes to propagate a Join/Prune(S,G) message to an I-IP
upstream router, the AFBR MUST translate Join/Prune(S,G) messages upstream router, the AFBR MUST translate Join/Prune(S,G) messages
into Join/Prune(S',G') messages following the rules specified above, into Join/Prune(S',G') messages following the rules specified above,
then send the latter. then send the latter.
6.3. I-IP (S',G') State Maintenance 6.3. I-IP (S',G') State Maintenance
It is possible that I-IP transit core runs other non-transit I-IP It is possible that the I-IP transit core runs another non-transit
PIM-SSM instance. Since the translated source address starts with I-IP PIM-SSM instance. Since the translated source address starts
the unique "Well-Known" prefix or the ISP-defined prefix that SHOULD with the unique "Well-Known" prefix or the ISP-defined prefix that
NOT be used otherwise, mesh multicast will not influence non-transit SHOULD NOT be used by other service provider, mesh multicast will not
PIM-SSM multicast at all. When one AFBR receives an I-IP (S',G') influence non-transit PIM-SSM multicast at all. When an AFBR
message, it MUST check S'. If S' starts with the unique prefix, it receives an I-IP (S',G') message, it MUST check S'. If S' starts
means that this message is actually a translated E-IP (S,G) or (*,G) with the unique prefix, then the message is actually a translated
message, then the AFBR MUST translate this message back to E-IP PIM E-IP (S,G) or (*,G) message, and the AFBR MUST translate this message
message and process it. back to E-IP PIM message and process it.
6.4. E-IP (S,G,rpt) State Maintenance 6.4. E-IP (S,G,rpt) State Maintenance
When an AFBR wishes to propagate a Join/Prune(S,G,rpt) message to an When an AFBR wishes to propagate a Join/Prune(S,G,rpt) message to an
I-IP upstream router, the AFBR MUST do as specified in Section 6.5 I-IP upstream router, the AFBR MUST operate as specified in
and Section 6.6. Section 6.5 and Section 6.6.
6.5. Inter-AFBR Signaling 6.5. Inter-AFBR Signaling
Assume that one downstream AFBR has joined a RPT of (*,G) and a SPT Assume that one downstream AFBR has joined a RPT of (*,G) and a SPT
of (S,G), and decide to perform a SPT switchover. According to of (S,G), and decide to perform a SPT switchover. According to
[RFC7761], it SHOULD propagate a Prune(S,G,rpt) message along with [RFC7761], it SHOULD propagate a Prune(S,G,rpt) message along with
the periodical Join(*,G) message upstream towards RP. Unfortunately, the periodical Join(*,G) message upstream towards RP. However,
routers in I-IP transit core are not supposed to understand (S,G,rpt) routers in the I-IP transit core do not process (S,G,rpt) messages
messages since I-IP transit core is treated as SSM-only. As a since the I-IP transit core is treated as SSM-only. As a result, the
result, this downstream AFBR is unable to prune S from this RPT, then downstream AFBR is unable to prune S from this RPT, so it will
it will receive two copies of the same data of (S,G). In order to receive two copies of the same data of (S,G). In order to solve this
solve this problem, we introduce a new mechanism for downstream AFBRs problem, we introduce a new mechanism for downstream AFBRs to inform
to inform upstream AFBRs of pruning any given S from RPT. upstream AFBRs of pruning any given S from an RPT.
When a downstream AFBR wishes to propagate a (S,G,rpt) message When a downstream AFBR wishes to propagate a (S,G,rpt) message
upstream, it SHOULD encapsulate the (S,G,rpt) message, then send the upstream, it SHOULD encapsulate the (S,G,rpt) message, then send the
encapsulated unicast message to the corresponding upstream AFBR, encapsulated unicast message to the corresponding upstream AFBR,
which we call "RP'". which we call "RP'".
When RP' receives this encapsulated message, it SHOULD decapsulate When RP' receives this encapsulated message, it SHOULD decapsulate
this message as what it does in the unicast scenario, and get the the message as in the unicast scenario, and retrieve the original
original (S,G,rpt) message. The incoming interface of this message (S,G,rpt) message. The incoming interface of this message may be
may be different from the outgoing interface which propagates different to the outgoing interface which propagates multicast data
multicast data to the corresponding downstream AFBR, and there may be to the corresponding downstream AFBR, and there may be other
other downstream AFBRs that need to receive multicast data of (S,G) downstream AFBRs that need to receive multicast data of (S,G) from
from this incoming interface, so RP' SHOULD NOT simply process this this incoming interface, so RP' SHOULD NOT simply process this
message as specified in [RFC7761] on the incoming interface. message as specified in [RFC7761] on the incoming interface.
To solve this problem and keep the solution as simple as possible, we To solve this problem as simply as possible, we introduce an
introduce an "interface agent" to process all the encapsulated "interface agent" to process all the encapsulated (S,G,rpt) messages
(S,G,rpt) messages the upstream AFBR receives, and prune S from the the upstream AFBR receives, and prune S from the RPT of group G when
RPT of group G when no downstream AFBR wants to receive multicast no downstream AFBR is subscribed to receive multicast data of (S,G)
data of (S,G) along the RPT. In this way, we do insure that along the RPT. In this way, we ensure that downstream AFBRs will not
downstream AFBRs will not miss any multicast data that they need, at miss any multicast data that they need, at the cost of duplicated
the cost of duplicated multicast data of (S,G) along the RPT received multicast data of (S,G) along the RPT received by SPT-switched-over
by SPT-switched-over downstream AFBRs, if there exists at least one downstream AFBRs, if at least one downstream AFBR exists that has not
downstream AFBR that has not yet sent Prune(S,G,rpt) messages to the yet sent Prune(S,G,rpt) messages to the upstream AFBR. The following
upstream AFBR. The following diagram shows an example of how an diagram shows an example of how an "interface agent" MAY be
"interface agent" MAY be implemented: implemented:
+----------------------------------------+ +----------------------------------------+
| | | |
| +-----------+----------+ | | +-----------+----------+ |
| | PIM-SM | UDP | | | | PIM-SM | UDP | |
| +-----------+----------+ | | +-----------+----------+ |
| ^ | | | ^ | |
| | | | | | | |
| | v | | | v |
| +----------------------+ | | +----------------------+ |
| | I/F Agent | | | | I/F Agent | |
| +----------------------+ | | +----------------------+ |
| PIM ^ | multicast | | PIM ^ | multicast |
| messages | | data | | messages | | data |
| | +-------------+---+ | | | +-------------+---+ |
skipping to change at page 16, line 34 skipping to change at page 16, line 39
| +--------- + +----------+ | | +--------- + +----------+ |
| | I-IP I/F | | I-IP I/F | | | | I-IP I/F | | I-IP I/F | |
| +----------+ +----------+ | | +----------+ +----------+ |
| ^ | ^ | | | ^ | ^ | |
| | | | | | | | | | | |
+--------|-----|----------|-----|--------+ +--------|-----|----------|-----|--------+
| v | v | v | v
Figure 7: Interface Agent Implementation Example Figure 7: Interface Agent Implementation Example
Figure 7 shows an example of interface agent implementation where we Figure 7 shows an example of interface agent implementation using UDP
choose UDP encapsulation. The interface agent has two encapsulation. The interface agent has two responsibilities: In the
responsibilities: In the control plane, it SHOULD work as a real control plane, it SHOULD work as a real interface that has joined
interface that has joined (*,G) in representative of all the I-IP (*,G), representing of all the I-IP interfaces which are outgoing
interfaces which are outgoing interfaces of (*,G) state machine, and interfaces of the (*,G) state machine, and process the (S,G,rpt)
process the (S,G,rpt) messages received from all the I-IP interfaces. messages received from all the I-IP interfaces. The interface agent
The interface agent maintains downstream (S,G,rpt) state machines of maintains downstream (S,G,rpt) state machines of every downstream
every downstream AFBR, and submits Prune(S,G,rpt) messages to the AFBR, and submits Prune (S,G,rpt) messages to the PIM-SM module only
PIM-SM module only when every (S,G,rpt) state machine is at Prune(P) when every (S,G,rpt) state machine is at Prune(P) or PruneTmp(P')
or PruneTmp(P') state, which means that no downstream AFBR wants to state, which means that no downstream AFBR is subscribed to receive
receive multicast data of (S,G) along the RPT of G. Once a (S,G,rpt) multicast data of (S,G) along the RPT of G. Once a (S,G,rpt) state
state machine changes to NoInfo(NI) state, which means that the machine changes to NoInfo(NI) state, which means that the
corresponding downstream AFBR has changed its mind to receive corresponding downstream AFBR has switched to receive multicast data
multicast data of (S,G) along the RPT again, the interface agent of (S,G) along the RPT again, the interface agent SHOULD send a Join
SHOULD send a Join(S,G,rpt) to PIM-SM module immediately; In the data (S,G,rpt) to the PIM-SM module immediately; In the data plane, upon
plane, upon receiving a multicast data packet, the interface agent receiving a multicast data packet, the interface agent SHOULD
SHOULD encapsulate it at first, then propagate the encapsulated encapsulate it at first, then propagate the encapsulated packet from
packet onto every I-IP interface. every I-IP interface.
NOTICE: There may exist an E-IP neighbor of RP' that has joined the NOTICE: It is possible that an E-IP neighbor of RP' that has joined
RPT of G, so the per-interface state machine for receiving E-IP Join/ the RPT of G, so the per-interface state machine for receiving E-IP
Prune(S,G,rpt) messages SHOULD still take effect. Join/Prune (S,G,rpt) messages SHOULD keep alive.
6.6. SPT Switchover 6.6. SPT Switchover
After a new AFBR expresses its interest in receiving traffic destined After a new AFBR expresses its interest in receiving traffic destined
for a multicast group, it will receive all the data from the RPT at for a multicast group, it will receive all the data from the RPT at
first. At this time, every downstream AFBR will receive multicast first. At this time, every downstream AFBR will receive multicast
data from any source from this RPT, in spite of whether they have data from any source from this RPT, in spite of whether they have
switched over to SPT of some source(s) or not. switched over to an SPT of some source(s) or not.
To minimize this redundancy, it is recommended that every AFBR's To minimize this redundancy, it is recommended that every AFBR's
SwitchToSptDesired(S,G) function employs the "switch on first packet" SwitchToSptDesired(S,G) function employs the "switch on first packet"
policy. In this way, the delay of switchover to SPT is kept as policy. In this way, the delay in switchover to SPT is kept as small
little as possible, and after the moment that every AFBR has as possible, and after the moment that every AFBR has performed the
performed the SPT switchover for every S of group G, no data will be SPT switchover for every S of group G, no data will be forwarded in
forwarded in the RPT of G, thus no more redundancy will be produced. the RPT of G, thus no more redundancy will be produced.
6.7. Other PIM Message Types 6.7. Other PIM Message Types
Apart from Join or Prune, there exists other message types including Apart from Join or Prune, other message types exist, including
Register, Register-Stop, Hello and Assert. Register and Register- Register, Register-Stop, Hello and Assert. Register and Register-
Stop messages are sent by unicast, while Hello and Assert messages Stop messages are sent by unicast, while Hello and Assert messages
are only used between directly linked routers to negotiate with each are only used between directly linked routers to negotiate with each
other. It is not necessary to translate them for forwarding, thus other. It is not necessary to translate these for forwarding, thus
the process of these messages is out of scope for this document. the processing of these messages is out of scope for this document.
6.8. Other PIM States Maintenance 6.8. Other PIM States Maintenance
Apart from states mentioned above, there exists other states Apart from states mentioned above, other states exist, including
including (*,*,RP) and I-IP (*,G') state. Since we treat I-IP core (*,*,RP) and I-IP (*,G') state. Since we treat the I-IP core as SSM-
as SSM-only, the maintenance of these states is out of scope for this only, the maintenance of these states is out of scope for this
document. document.
7. Data Plane Functions of AFBR 7. Data Plane Functions of the AFBR
7.1. Process and Forward Multicast Data 7.1. Process and Forward Multicast Data
On receiving multicast data from upstream routers, the AFBR looks up On receiving multicast data from upstream routers, the AFBR checks
its forwarding table to check the IP address of each outgoing its forwarding table to find the IP address of each outgoing
interface. If there exists at least one outgoing interface whose IP interface. If there is at least one outgoing interface whose IP
address family is different from the incoming interface, the AFBR address family is different from the incoming interface, the AFBR
MUST encapsulate/decapsulate this packet and forward it to such MUST encapsulate/decapsulate this packet and forward it via the
outgoing interface(s), then forward the data to other outgoing outgoing interface(s), then forward the data via other outgoing
interfaces without encapsulation/decapsulation. interfaces without encapsulation/decapsulation.
When a downstream AFBR that has already switched over to SPT of S When a downstream AFBR that has already switched over to the SPT of S
receives an encapsulated multicast data packet of (S,G) along the receives an encapsulated multicast data packet of (S,G) along the
RPT, it SHOULD silently drop this packet. RPT, it SHOULD silently drop this packet.
7.2. Selecting a Tunneling Technology 7.2. Selecting a Tunneling Technology
Choosing tunneling technology depends on the policies configured at Choosing tunneling technology depends on the policies configured on
AFBRs. It is recommended that all AFBRs use the same technology, AFBRs. It is REQUIRED that all AFBRs use the same technology,
otherwise some AFBRs may not be able to decapsulate encapsulated otherwise some AFBRs SHALL not be able to decapsulate encapsulated
packets from other AFBRs that use a different tunneling technology. packets from other AFBRs that use a different tunneling technology.
7.3. TTL 7.3. TTL
Processing of TTL depends on the tunneling technology, and it is out Processing of TTL depends on the tunneling technology, and it is out
of scope of this document. of scope of this document.
7.4. Fragmentation 7.4. Fragmentation
The encapsulation performed by upstream AFBR will increase the size The encapsulation performed by an upstream AFBR will increase the
of packets. As a result, the outgoing I-IP link MTU may not size of packets. As a result, the outgoing I-IP link MTU may not
accommodate the extra size. As it is not always possible for core accommodate the larger packet size. As it is not always possible for
operators to increase the MTU of every link. Fragmentation and core operators to increase the MTU of every link. Fragmentation
reassembling of encapsulated packets MUST be supported by AFBRs. after encapsulation and reassembling of encapsulated packets MUST be
supported by AFBRs [RFC5565].
8. Packet Format and Translation 8. Packet Format and Translation
Because PIM-SM Specification is independent of the underlying unicast Because the PIM-SM Specification is independent of the underlying
routing protocol, the packet format in Section 4.9 of [RFC7761] unicast routing protocol, the packet format in Section 4.9 of
remains the same, except that the group address and source address [RFC7761] remains the same, except that the group address and source
MUST be translated when traversing AFBR. address MUST be translated when traversing AFBR.
For example, Figure 8 shows the register-stop message format in IPv4 For example, Figure 8 shows the register-stop message format in IPv4
and IPv6 address family. and IPv6 address family.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type | Reserved | Checksum | |PIM Ver| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Group Address (Encoded-Group format) | | IPv4 Group Address (Encoded-Group format) |
skipping to change at page 19, line 30 skipping to change at page 19, line 30
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Group Address (Encoded-Group format) | | IPv6 Group Address (Encoded-Group format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Source Address (Encoded-Unicast format) | | IPv6 Source Address (Encoded-Unicast format) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(2). IPv6 Register-Stop Message Format (2). IPv6 Register-Stop Message Format
Figure 8: Register-Stop Message Format Figure 8: Register-Stop Message Format
In Figure 8, the semantics of fields "PIM Ver", "Type", "Reserved", In Figure 8, the semantics of fields "PIM Ver", "Type", "Reserved",
"Checksum" remain the same. and "Checksum" remain the same.
IPv4 Group Address (Encoded-Group format): The encoded-group format IPv4 Group Address (Encoded-Group format): The encoded-group format
of the IPv4 group address mentioned in Section 4.2 and 5.2. of the IPv4 group address described in Section 4.2 and 5.2.
IPv4 Source Address (Encoded-Group format): The encoded-unicast IPv4 Source Address (Encoded-Group format): The encoded-unicast
format of the IPv4 source address mentioned in Section 4.3 and 5.3. format of the IPv4 source address described in Section 4.3 and 5.3.
IPv6 Group Address (Encoded-Group format): The encoded-group format IPv6 Group Address (Encoded-Group format): The encoded-group format
of the IPv6 group address mentioned in Section 4.2 and 5.2. of the IPv6 group address described in Section 4.2 and 5.2.
IPv6 Source Address (Encoded-Group format): The encoded-unicast IPv6 Source Address (Encoded-Group format): The encoded-unicast
format of the IPv6 source address mentioned in Section 4.3 and 5.3. format of the IPv6 source address described in Section 4.3 and 5.3.
9. Softwire Mesh Multicast Encapsulation 9. Softwire Mesh Multicast Encapsulation
Softwire mesh multicast encapsulation does not require the use of any Softwire mesh multicast encapsulation does not require the use of any
one particular encapsulation mechanism. Rather, it MUST accommodate one particular encapsulation mechanism. Rather, it must accommodate
a variety of different encapsulation mechanisms, and MUST allow the a variety of different encapsulation mechanisms, and allow the use of
use of encapsulation mechanisms mentioned in [RFC4925]. encapsulation mechanisms mentioned in [RFC4925]. Additionally, all
of the AFBRs attached to the I-IP network MUST implement the same
encapsulation mechanism.
10. Security Considerations 10. Security Considerations
Some schemes will place heavy burden on routers, which can be used by The security concerns raised in [RFC4925] and [RFC7761] are
attackers as a tool when they carry out DDoS attack. Compared with applicable here. In addition, the additional workload associated
[RFC4925], the security concerns SHOULD be considered more carefully. with some schemes could be exploited by an attacker to perform a out
The attackers can set up many multicast trees in the edge networks, DDoS attack. Compared with [RFC4925], the security concerns SHOULD
causing too many multicast states in the core network. be considered more carefully: an attacker could potentially set up
many multicast trees in the edge networks, causing too many multicast
Besides, this document does not introduce any new security concern in states in the core network.
addition to what is discussed in [RFC4925] and [RFC7761].
11. IANA Considerations 11. IANA Considerations
When AFBRs perform address mapping, they follow some predefined This document includes no request to IANA.
rules, especially the IPv6 prefix for source address mapping should
be predefined, such that ingress AFBRs and egress AFBRs can complete
the mapping procedure correctly. The IPv6 prefix for translation can
be unified within only the transit core, or within global area. In
the later condition, the prefix MUST be assigned by IANA.
12. References 12. References
12.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
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