Network Working Group D. Thaler
Internet-Draft M. Talwar
Intended status: Standards Track A. Aggarwal
Expires: September 8, 2010 Microsoft Corporation
L. Vicisano
Qualcomm Inc.
T. Pusateri
!j
March 7, 2010
Automatic IP Multicast Without Explicit Tunnels (AMT)
draft-ietf-mboned-auto-multicast-10
Abstract
Automatic Multicast Tunneling (AMT) allows multicast communication
amongst isolated multicast-enabled sites or hosts, attached to a
network which has no native multicast support. It also enables them
to exchange multicast traffic with the native multicast
infrastructure and does not require any manual configuration. AMT
uses an encapsulation interface so that no changes to a host stack or
applications are required, all protocols (not just UDP) are handled,
and there is no additional overhead in core routers.
Status of this Memo
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This Internet-Draft will expire on September 8, 2010.
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements notation . . . . . . . . . . . . . . . . . . . . 7
4. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. AMT Pseudo-Interface . . . . . . . . . . . . . . . . . . . 8
4.2. AMT Gateway . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. AMT Site . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.4. AMT Relay Router . . . . . . . . . . . . . . . . . . . . . 8
4.5. AMT Relay Anycast Prefix . . . . . . . . . . . . . . . . . 9
4.6. AMT Relay Anycast Address . . . . . . . . . . . . . . . . 9
4.7. AMT Subnet Anycast Prefix . . . . . . . . . . . . . . . . 9
4.8. AMT Gateway Anycast Address . . . . . . . . . . . . . . . 9
5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Receiving Multicast in an AMT Site . . . . . . . . . . . . 10
5.1.1. Scalability Considerations . . . . . . . . . . . . . . 11
5.1.2. Spoofing Considerations . . . . . . . . . . . . . . . 11
5.1.3. Protocol Sequence for a Gateway Joining SSM
Receivers to a Relay . . . . . . . . . . . . . . . . . 12
5.2. Sourcing Multicast from an AMT site . . . . . . . . . . . 14
5.2.1. Supporting Site-MBone Multicast . . . . . . . . . . . 15
5.2.2. Supporting Site-Site Multicast . . . . . . . . . . . . 16
6. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 17
6.1. AMT Relay Discovery . . . . . . . . . . . . . . . . . . . 17
6.1.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.1.2. Reserved . . . . . . . . . . . . . . . . . . . . . . . 17
6.1.3. Discovery Nonce . . . . . . . . . . . . . . . . . . . 17
6.2. AMT Relay Advertisement . . . . . . . . . . . . . . . . . 17
6.2.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.2.2. Reserved . . . . . . . . . . . . . . . . . . . . . . . 18
6.2.3. Discovery Nonce . . . . . . . . . . . . . . . . . . . 18
6.2.4. Relay Address . . . . . . . . . . . . . . . . . . . . 18
6.3. AMT Request . . . . . . . . . . . . . . . . . . . . . . . 18
6.3.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.3.2. Reserved . . . . . . . . . . . . . . . . . . . . . . . 19
6.3.3. Request Nonce . . . . . . . . . . . . . . . . . . . . 19
6.4. AMT Membership Query . . . . . . . . . . . . . . . . . . . 19
6.4.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.4.2. Reserved . . . . . . . . . . . . . . . . . . . . . . . 20
6.4.3. Response MAC . . . . . . . . . . . . . . . . . . . . . 20
6.4.4. Request Nonce . . . . . . . . . . . . . . . . . . . . 20
6.4.5. IGMP/MLD Query (including IP Header) . . . . . . . . . 20
6.5. AMT Membership Update . . . . . . . . . . . . . . . . . . 21
6.5.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.5.2. Reserved . . . . . . . . . . . . . . . . . . . . . . . 22
6.5.3. Response MAC . . . . . . . . . . . . . . . . . . . . . 22
6.5.4. Request Nonce . . . . . . . . . . . . . . . . . . . . 22
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6.5.5. IGMP/MLD Message (including IP Header) . . . . . . . . 22
6.6. AMT IP Multicast Data . . . . . . . . . . . . . . . . . . 22
6.6.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.6.2. Reserved . . . . . . . . . . . . . . . . . . . . . . . 23
6.6.3. IP Multicast Data . . . . . . . . . . . . . . . . . . 23
6.7. AMT Membership Teardown . . . . . . . . . . . . . . . . . 23
6.7.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.7.2. Reserved . . . . . . . . . . . . . . . . . . . . . . . 24
6.7.3. Original Response MAC . . . . . . . . . . . . . . . . 24
6.7.4. Original Request Nonce . . . . . . . . . . . . . . . . 24
6.7.5. Original Source Port . . . . . . . . . . . . . . . . . 24
6.7.6. Source AFI . . . . . . . . . . . . . . . . . . . . . . 24
6.7.7. Original Source Address . . . . . . . . . . . . . . . 25
6.7.8. IGMP/MLD Message (including IP Header) . . . . . . . . 25
7. AMT Gateway Details . . . . . . . . . . . . . . . . . . . . . 26
7.1. At Startup Time . . . . . . . . . . . . . . . . . . . . . 26
7.2. Gateway Group and Source Addresses . . . . . . . . . . . . 26
7.2.1. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.2.2. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.3. Joining Groups with MBone Sources . . . . . . . . . . . . 28
7.4. Responding to Relay Changes . . . . . . . . . . . . . . . 28
7.5. Joining SSM Groups with AMT Gateway Sources . . . . . . . 29
7.6. Receiving AMT Membership Updates by the Gateway . . . . . 29
7.7. Sending data to SSM groups . . . . . . . . . . . . . . . . 29
8. Relay Router Details . . . . . . . . . . . . . . . . . . . . . 30
8.1. At Startup time . . . . . . . . . . . . . . . . . . . . . 30
8.2. Receiving Relay Discovery messages sent to the Anycast
Address . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.3. Receiving Membership Updates from AMT Gateways . . . . . . 30
8.4. Receiving (S,G) Joins from the Native Side, for AMT
Sources . . . . . . . . . . . . . . . . . . . . . . . . . 31
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
9.1. IPv4 and IPv6 Anycast Prefix Allocation . . . . . . . . . 32
9.1.1. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.1.2. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.2. IPv4 and IPv6 AMT Subnet Prefix Allocation . . . . . . . . 32
9.2.1. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.2.2. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.3. UDP Port number . . . . . . . . . . . . . . . . . . . . . 32
10. Security Considerations . . . . . . . . . . . . . . . . . . . 33
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 34
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
13.1. Normative References . . . . . . . . . . . . . . . . . . . 36
13.2. Informative References . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
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1. Introduction
The primary goal of this document is to foster the deployment of
native IP multicast by enabling a potentially large number of nodes
to connect to the already present multicast infrastructure.
Therefore, the techniques discussed here should be viewed as an
interim solution to help in the various stages of the transition to a
native multicast network.
To allow fast deployment, the solution presented here only requires
small and concentrated changes to the network infrastructure, and no
changes at all to user applications or to the socket API of end-
nodes' operating systems. The protocol introduced in this
specification can be deployed in a few strategically-placed network
nodes and in user-installable software modules (pseudo device drivers
and/or user-mode daemons) that reside underneath the socket API of
end-nodes' operating systems. This mechanism is very similar to that
used by "6to4" [RFC3056], [RFC3068] to get automatic IPv6
connectivity.
Effectively, AMT treats the unicast-only inter-network as a large
non-broadcast multi-access (NBMA) link layer, over which we require
the ability to multicast. To do this, multicast packets being sent
to or from a site must be encapsulated in unicast packets. If the
group has members in multiple sites, AMT encapsulation of the same
multicast packet will take place multiple times by necessity.
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2. Applicability
AMT is not a substitute for native multicast or a statically
configured multicast tunnel for high traffic flow. Unicast
replication is required to reach multiple receivers that are not part
of the native multicast infrastructure. Unicast replication is also
required by non-native sources to different parts of the native
multicast infrastructure. However, this is no worse than regular
unicast distribution of streams and in most cases much better.
The following problems are addressed:
1. Allowing isolated sites/hosts to receive the SSM flavor of
multicast ([RFC4607]).
2. Allowing isolated non-NAT sites/hosts to transmit the SSM flavor
of multicast.
3. Allowing isolated sites/hosts to receive general multicast (ASM
[RFC1112]).
This document does not address allowing isolated sites/hosts to
transmit general multicast. We expect that other solutions (e.g.,
Tunnel Brokers, a la [RFC3053]) will be used for sites that desire
this capability.
Implementers should be aware that site administrators may have
configured administratively scoped multicast boundaries and a remote
gateway may provide a means to circumvent administrative boundaries.
Therefore, implementations should allow for the configuration of such
boundaries on relays and gateways and perform filtering as needed.
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3. Requirements notation
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 [RFC2119].
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4. Definitions
+---------------+ Internet +---------------+
| AMT Site | | Native MCast |
| | | |
| +------+----+ AMT +----+----+ AMT |
| |AMT Gateway| Anycast |AMT Relay| Subnet |
| | +-----+-+ Prefix +-+-----+ | Prefix |
| | |AMT IF | <------------|AMT IF | |--------> |
| | +-----+-+ +-+-----+ | |
| +------+----+ +----+----+ |
| | | |
+---------------+ +---------------+
4.1. AMT Pseudo-Interface
AMT encapsulation of multicast packets inside unicast packets occurs
at a point that is logically equivalent to an interface, with the
link layer being the unicast-only network. This point is referred to
as a pseudo-interface. Some implementations may treat it exactly
like any other interface and others may treat it like a tunnel end-
point.
4.2. AMT Gateway
A host, or a site gateway router, supporting an AMT Pseudo-
Interface. It does not have native multicast connectivity to the
native multicast backbone infrastructure. It is simply referred to
in this document as a "gateway".
4.3. AMT Site
A multicast-enabled network not connected to the multicast backbone
served by an AMT Gateway. It could also be a stand- alone AMT
Gateway.
4.4. AMT Relay Router
A multicast router configured to support transit routing between AMT
Sites and the native multicast backbone infrastructure. The relay
router has one or more interfaces connected to the native multicast
infrastructure, zero or more interfaces connected to the non-
multicast capable inter-network, and an AMT pseudo-interface. It is
simply referred to in this document as a "relay".
As with [RFC3056], we assume that normal multicast routers do not
want to be tunnel endpoints (especially if this results in high fan
out), and similarly that service providers do not want encapsulation
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to arbitrary routers. Instead, we assume that special-purpose
routers will be deployed that are suitable for serving as relays.
4.5. AMT Relay Anycast Prefix
A well-known address prefix used to advertise (into the unicast
routing infrastructure) a route to an available AMT Relay Router.
This could also be private (i.e., not well-known) for a private
relay.
Prefixes for both IPv4 and IPv6 will be assigned in a future version
of this draft.
4.6. AMT Relay Anycast Address
An anycast address which is used to reach the nearest AMT Relay
Router.
This address corresponds to the setting the low-order octet of the
AMT Relay Anycast Prefix to 1 (for both IPv4 and IPv6).
4.7. AMT Subnet Anycast Prefix
A well-known address prefix used to advertise (into the M-RIB of the
native multicast-enabled infrastructure) a route to AMT Sites. This
prefix will be used to enable sourcing SSM traffic from an AMT
Gateway.
4.8. AMT Gateway Anycast Address
An anycast address in the AMT Subnet Anycast Prefix range, which is
used by an AMT Gateway to enable sourcing SSM traffic from local
applications.
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5. Overview
5.1. Receiving Multicast in an AMT Site
Internet
+---------------+ +---------------+
| AMT Site | 2. 3-way Membership | MBone |
| | Handshake | |
| 1. Join +---+---+ =================> +---+---+ |
| +---->|Gateway| | Relay | |
| | +---+---+ <================= +---+---+ |
| R-+ | 3. Receive Data | |
+---------------+ +---------------+
Receiving Multicast in an AMT Site
AMT relays and gateways cooperate to transmit multicast traffic
sourced within the native multicast infrastructure to AMT sites:
relays receive the traffic natively and unicast-encapsulate it to
gateways; gateways decapsulate the traffic and possibly forward it
into the AMT site.
Each gateway has an AMT pseudo-interface that serves as a default
multicast route. Requests to join a multicast session are sent to
this interface and encapsulated to a particular relay reachable
across the unicast-only infrastructure.
Each relay has an AMT pseudo-interface too. Multicast traffic sent
on this interface is encapsulated to zero or more gateways that have
joined to the relay. The AMT recipient-list is determined for each
multicast session. This requires the relay to keep state for each
gateway which has joined a particular group or (source, group) pair.
Multicast packets from the native infrastructure behind the relay
will be sent to each gateway which has requested them.
All multicast packets (data and control) are encapsulated in unicast
packets. UDP encapsulation is used for all AMT control and data
packets using the IANA reserved UDP port number for AMT.
Each relay, plus the set of all gateways using the relay, together
are thought of as being on a separate logical NBMA link. This
implies that the AMT recipient-list is a list of "link layer"
addresses which are (IP address, UDP port) pairs.
Since the number of gateways using a relay can be quite large, and we
expect that most sites will not want to receive most groups, an
explicit-joining protocol is required for gateways to communicate
group membership information to a relay. The two most likely
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candidates are the IGMP/MLD protocol [RFC3376], [RFC3810], and the
PIM-Sparse Mode protocol [RFC4601]. Since an AMT gateway may be a
host, and hosts typically do not implement routing protocols,
gateways will use IGMP/MLD as described in Section 7 below. This
allows a host kernel (or a pseudo device driver) to easily implement
AMT gateway behavior, and obviates the relay from the need to know
whether a given gateway is a host or a router. From the relay's
perspective, all gateways are indistinguishable from hosts on an NBMA
leaf network.
5.1.1. Scalability Considerations
It is possible that millions of hosts will enable AMT gateway
functionality and so an important design goal is not to create
gateway state in each relay until the gateway joins a multicast
group. But even the requirement that a relay keep group state per
gateway that has joined a group introduces potential scalability
concerns.
Scalability of AMT can be achieved by adding more relays, and using
an appropriate relay discovery mechanism for gateways to discover
relays. The solution we adopt is to assign addresses in anycast
fashion to relays [RFC1546], [RFC4291]. However, simply sending
periodic membership reports to an anycast address can cause
duplicates. Specifically, if routing changes such that a different
relay receives a periodic membership report, both the new and old
relays will encapsulate data to the AMT site until the old relay's
state times out. This is obviously undesirable. Instead, we use the
anycast address merely to find the unicast address of a relay to
which membership reports are sent.
Since adding another relay has the result of adding another
independent NBMA link, this allows the gateways to be spread out
among more relays so as to keep the number of gateways per relay at a
reasonable level.
5.1.2. Spoofing Considerations
An attacker could affect the group state in the relay or gateway by
spoofing the source address in the join or leave reports. This can
be used to launch reflection or denial of service attacks on the
target. Such attacks can be mitigated by using a three way handshake
between the gateway and the relay for each multicast membership
report or leave.
When a gateway or relay wants to send a membership report, it first
sends an AMT Request with a request nonce in it. The receiving side
(the respondent) can calculate a message authentication code (MAC)
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based on (for example) the source IP address of the Request, the
source UDP port, the request nonce, and a secret key known only to
the respondent. The algorithm and the input used to calculate the
MAC does not have to be standardized since the respondent generates
and verifies the MAC and the originator simply echoes it.
An AMT Membership Query is sent back including the request nonce and
the MAC to the originator of the Request. The originator then sends
the IGMP/MLD Membership/Listener Report or Leave/Done (including the
IP Header) along with the request nonce and the received MAC back to
the respondent finalizing the 3-way handshake.
Upon reception, the respondent can recalculate the MAC based on the
source IP address, the source UDP port, the request nonce, and the
local secret. The IGMP/MLD message is only accepted if the received
MAC matches the calculated MAC.
The local secret never has to be shared with the other side. It is
only used to verify return routability of the originator.
Since the same Request Nonce and source IP address can be re-used,
the receiver SHOULD change its secret key at least once per hour.
However, AMT Membership updates received with the previous secret
MUST be accepted for up to the IGMP/MLD Query Interval.
The condition might occur where the gateway or relay that initially
sent the AMT Request dynamically changes its IP address. This might
occur due to a change in wireless networks, a DHCP assignment, or
another network failure. When this occurs, it is no longer possible
to verify the MAC using the source address and source port. Though,
in order to reduce state, it is desirable to tear down the state that
was created with the old source address. A Teardown message with
special considerations for calculating the MAC is described below to
perform this function.
5.1.3. Protocol Sequence for a Gateway Joining SSM Receivers to a Relay
This description assumes the Gateway can be a host joining as a
receiver or a network device acting as a Gateway when a directly
connected host joins as a receiver.
o Receiver at AMT site sends IGMPv3/MLDv2 report joining (S1,G1).
o Gateway receives report. If it has no tunnel state with a Relay,
it originates an AMT Relay Discovery message addressed to the
Anycast Relay IP address. The AMT Relay Discovery message can be
sent on demand if no relay is known at this time or at startup and
be periodically refreshed.
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o The closest Relay topologically receives the AMT Relay Discovery
message and returns the nonce from the Discovery in an AMT Relay
Advertisement message so the Gateway can learn of the Relay's
unique IP address.
o When the Gateway receives the AMT Relay Advertisement message, it
now has an address to use for all subsequent (S,G) entries it will
join on behalf of attached receivers (or itself).
o If the gateway has a valid Response MAC from a previous AMT Query
message, it can send an AMT Membership Update message as described
below. Otherwise, the Gateway sends an AMT Request message to the
Relay's unique IP address to begin the process of joining the
(S,G). The gateway also SHOULD initialize a timer used to send
periodic Requests to a random value from the interval [0, [Query
Interval]] before sending the first periodic report, in order to
prevent startup synchronization.
o The Relay responds to the AMT Request message by returning the
nonce from the Request in a AMT Query message. The Query message
contains an IGMP/MLD QUERY indicating how often the Gateway should
repeat AMT Request messages so the (S,G) state can stay refreshed
in the Relay. The Query message also includes an opaque security
code which is generated locally (with no external coordination).
o When the Gateway receives the AMT Query message it responds by
copying the security code from the AMT Query message into a AMT
Membership Update message. The Update message contains (S1,G1) in
an IGMPv3/MLDv2 formatted packet with an IP header. The nonce
from the AMT Request is also included in the AMT Membership Update
message.
o When the Relay receives the AMT Membership Update, it will add the
tunnel to the Gateway in it's outgoing interface list for it's
(S1,G1) entry stored in the multicast routing table. If the
(S1,G1) entry was created do to this interaction, the multicast
routing protocol running on the Relay will trigger a Join message
towards source S1 to build a native multicast tree in the native
multicast infrastructure.
o As packets are sent from the host S1, they will travel natively
down the multicast tree associated with (S1,G1) in the native
multicast infrastructure to the Relay. The Relay will replicate
to all interfaces in it's outgoing interface list as well as the
tunnel outgoing interface, which is encapsulated in a unicast AMT
Multicast Data message.
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o When the Gateway receives the AMT Multicast Data message, it will
accept the packet since it was received over the pseudo-interface
associated with the tunnel to the Relay it had attached to, and
forward the packet to the outgoing interfaces joined by any
attached receiver hosts (or deliver the packet to the application
when the Gateway is the receiver).
o If later (S2,G2) is joined by a receiver, a 3-way handshake of
Request/ Query/Update occurs for this entry. The Discovery/
Advertisement exchange is not required.
o To keep the state for (S1,G1) and (S2,G2) alive in the Relay, the
Gateway will send periodic AMT Membership Updates. The Membership
Update can be sent directly if the sender has a valid nonce from a
previous Request. If not, an AMT Request messages should be sent
to solicit a Query Message. When sending a periodic state
refresh, all joined state in the Gateway is packed in the fewest
number of AMT Membership Update messages.
o When the Gateway leaves all (S,G) entries, the Relay can free
resources associated with the tunnel. It is assumed that when the
Gateway would want to join an (S,G) again, it would start the
Discovery/Advertisement tunnel establishment process over again.
This same procedure would be used for receivers who operate in Any-
Source Multicast (ASM) mode.
5.2. Sourcing Multicast from an AMT site
Two cases are discussed below: multicast traffic sourced in an AMT
site and received in the MBone, and multicast traffic sourced in an
AMT site and received in another AMT site.
In both cases only SSM sources are supported. Furthermore this
specification only deals with the source residing directly in the
gateway. To enable a generic node in an AMT site to source
multicast, additional coordination between the gateway and the
source-node is required.
The gateway SHOULD allow for filtering link-local and site-local
traffic.
The general mechanism used to join towards AMT sources is based on
the following:
1. Applications residing in the gateway use addresses in the AMT
Subnet Anycast Prefix to send multicast, as a result of sourcing
traffic on the AMT pseudo-interface.
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2. The AMT Subnet Anycast Prefix is advertised for RPF reachability
in the M-RIB by relays and gateways.
3. Relays or gateways that receive a join for a source/group pair
use information encoded in the address pair to rebuild the
address of the gateway (source) to which to encapsulate the join
(see Section 7.2 for more details). The membership reports use
the same three way handshake as outlined in Section 5.1.2
5.2.1. Supporting Site-MBone Multicast
Internet
+---------------+ +---------------+
| AMT Site | 2. 3-way Membership | MBone |
| | Handshake | |
| +---+---+ <================= +---+---+ 1. Join |
| |Gateway| | Relay |<-----+ |
| +---+---+ =================> +---+---+ | |
| | 3. Receive Data | +-R |
+---------------+ +---------------+
Site-MBone Multicast
If a relay receives an explicit join from the native infrastructure,
for a given (source, group) pair where the source address belongs to
the AMT Subnet Anycast Prefix, then the relay will periodically
(using the rules specified in Section 5.1.2) encapsulate membership
updates for the group to the gateway. The gateway must keep state
per relay from which membership reports have been sent, and forward
multicast traffic from the site to all relays from which membership
reports have been received. The choice of whether this state and
replication is done at the link-layer (i.e., by the tunnel interface)
or at the network-layer is implementation dependent.
If there are multiple relays present, this ensures that data from the
AMT site is received via the closest relay to the receiver. This is
necessary when the routers in the native multicast infrastructure
employ Reverse-Path Forwarding (RPF) checks against the source
address, such as occurs when PIM Sparse-Mode [RFC4601] is used by the
multicast infrastructure.
The solution above will scale to an arbitrary number of relays, as
long at the number of relays requiring multicast traffic from a given
AMT site remains reasonable enough to not overly burden the site's
gateway.
A source at or behind an AMT gateway requires the gateway to do the
replication to one or more relays and receiving gateways. If this
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places too much of a burden on the sourcing gateway, the source
should join the native multicast infrastructure through a permanent
tunnel so that replication occurs within the native multicast
infrastructure.
5.2.2. Supporting Site-Site Multicast
Internet
+---------------+ +---------------+
| AMT Site | 2. 3-way Membership | AMT Site |
| | Handshake | |
| +---+---+ <================= +---+---+ 1. Join |
| |Gateway| |Gateway|<-----+ |
| +---+---+ =================> +---+---+ | |
| | 3. Receive Data | +-R |
+---------------+ +---------------+
Site-Site Multicast
Since we require gateways to accept membership reports, as described
above, it is also possible to support multicast among AMT sites,
without requiring assistance from any relays.
When a gateway wants to join a given (source, group) pair, where the
source address belongs to the AMT Subnet Anycast Prefix, then the
gateway will periodically unicast encapsulate an IGMPv3/MLDv2 Report
[RFC3376], [RFC3810] (including IP Header) directly to the site
gateway for the source.
We note that this can result in a significant amount of state at a
site gateway sourcing multicast to a large number of other AMT sites.
However, it is expected that this is not unreasonable for two
reasons. First, the gateway does not have native multicast
connectivity, and as a result is likely doing unicast replication at
present. The amount of state is thus the same as what such a site
already deals with. Secondly, any site expecting to source traffic
to a large number of sites could get a point-to-point tunnel to the
native multicast infrastructure, and use that instead of AMT.
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6. Message Formats
6.1. AMT Relay Discovery
The AMT Relay Discovery message is a UDP packet sent from the AMT
gateway unicast address to the AMT relay anycast address to discover
the unicast address of an AMT relay.
The UDP source port is uniquely selected by the local host operating
system. The UDP destination port is the IANA reserved AMT port
number. The UDP checksum MUST be valid in AMT control messages.
The payload of the UDP packet contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x1 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discovery Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AMT Relay Discovery
6.1.1. Type
The type of the message.
6.1.2. Reserved
A 24-bit reserved field. Sent as 0, ignored on receipt.
6.1.3. Discovery Nonce
A 32-bit random value generated by the gateway and replayed by the
relay.
6.2. AMT Relay Advertisement
The AMT Relay Advertisement message is a UDP packet sent from the AMT
relay anycast address to the source of the discovery message.
The UDP source port is the IANA reserved AMT port number and the UDP
destination port is the source port received in the Discovery
message. The UDP CHECKSUM MUST be valid in AMT control messages.
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The payload of the UDP packet contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x2 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discovery Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Relay Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AMT Relay Advertisement
6.2.1. Type
The type of the message.
6.2.2. Reserved
A 24-bit reserved field. Sent as 0, ignored on receipt.
6.2.3. Discovery Nonce
A 32-bit random value generated by the gateway and replayed by the
relay.
6.2.4. Relay Address
The unicast IPv4 or IPv6 address of the AMT relay. The family can be
determined by the length of the Advertisement.
6.3. AMT Request
A Request packet is sent to begin a 3-way handshake for sending an
IGMP/MLD Membership/Listener Report or Leave/Done. It can be sent
from a gateway to a relay, from a gateway to another gateway, or from
a relay to a gateway.
It is sent from the originator's unique unicast address to the
respondents' unique unicast address.
The UDP source port is uniquely selected by the local host operating
system. It can be different for each Request and different from the
source port used in Discovery messages but does not have to be. The
UDP destination port is the IANA reserved AMT port number. The UDP
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checksum MUST be valid in AMT control messages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x3 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AMT Relay Advertisement
6.3.1. Type
The type of the message.
6.3.2. Reserved
A 24-bit reserved field. Sent as 0, ignored on receipt.
6.3.3. Request Nonce
A 32-bit identifier used to distinguish this request.
6.4. AMT Membership Query
An AMT Membership Query packet is sent from the respondent back to
the originator to solicit an AMT Membership Update while confirming
the source of the original request. It contains a relay Message
Authentication Code (MAC) that is a cryptographic hash of a private
secret, the originators address, and the request nonce.
It is sent from the destination address received in the Request to
the source address received in the Request which is the same address
used in the Relay Advertisement.
The UDP source port is the IANA reserved AMT port number and the UDP
destination port is the source port received in the Request message.
The UDP checksum MUST be valid in AMT control messages.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x4 | Reserved | Response MAC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Response MAC (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IGMP Membership Query or MLD Listener Query |
| (including IP Header) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AMT Membership Query
6.4.1. Type
The type of the message.
6.4.2. Reserved
A 8-bit reserved field. Sent as 0, ignored on receipt.
6.4.3. Response MAC
A 48-bit hash generated by the respondent and sent to the originator
for inclusion in the AMT Membership Update. The algorithm used for
this is chosen by the respondent but an algorithm such as HMAC-MD5-48
[RFC2104] SHOULD be used at a minimum.
6.4.4. Request Nonce
A 32-bit identifier used to distinguish this request echoed back to
the originator.
6.4.5. IGMP/MLD Query (including IP Header)
The message contains either an IGMP Query or an MLD Multicast
Listener Query. The IGMP or MLD version sent should default to
IGMPv3 or MLDv2 unless explicitly configured to use IGMPv2 or MLDv1.
The IGMP/MLD Query includes a full IP Header. The IP source address
of the query would match the anycast address on the pseudo interface.
The TTL of the outer header should be sufficient to reach the tunnel
endpoint and not mimic the inner header TTL which is typically 1 for
IGMP/MLD messages.
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6.5. AMT Membership Update
An AMT Membership Update is sent to report a membership after a valid
Response MAC has been received. It contains the original IGMP/MLD
Membership/Listener Report or Leave/Done received over the AMT
pseudo-interface including the original IP header. It echoes the
Response MAC received in the AMT Membership Query so the respondent
can verify return routability to the originator.
It is sent from the destination address received in the Query to the
source address received in the Query which should both be the same as
the original Request.
The UDP source and destination port numbers should be the same ones
sent in the original Request.
The relay is not required to use the IP source address of the IGMP
Membership Report for any particular purpose.
The same Request Nonce and Response MAC can be used across multiple
AMT Membership Update messages without having to send individual AMT
Membership Query messages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x5 | Reserved | Response MAC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Response MAC (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IGMP or MLD Message (including IP header) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AMT Membership Update
6.5.1. Type
The type of the message.
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6.5.2. Reserved
A 8-bit reserved field. Sent as 0, ignored on receipt.
6.5.3. Response MAC
The 48-bit MAC received in the Membership Query and echoed back in
the Membership Update.
6.5.4. Request Nonce
A 32-bit identifier used to distinguish this request.
6.5.5. IGMP/MLD Message (including IP Header)
The message contains either an IGMP Membership Report, an IGMP
Membership Leave, an MLD Multicast Listener Report, or an MLD
Listener Done. The IGMP or MLD version sent should be in response
the version of the query received in the AMT Membership Query. The
IGMP/MLD Message includes a full IP Header.
6.6. AMT IP Multicast Data
The AMT Data message is a UDP packet encapsulating the IP Multicast
data requested by the originator based on a previous AMT Membership
Update message.
It is sent from the unicast destination address of the Membership
update to the source address of the Membership Update.
The UDP source and destination port numbers should be the same ones
sent in the original Query. The UDP checksum MUST be valid in AMT
control messages.
The payload of the UDP packet contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x6 | Reserved | IP Multicast Data ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AMT IP Multicast Data
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6.6.1. Type
The type of the message.
6.6.2. Reserved
An 8-bit reserved field. Sent as 0, ignored on receipt.
6.6.3. IP Multicast Data
The original IP Multicast data packet that is being replicated by the
relay to the gateways including the original IP header.
6.7. AMT Membership Teardown
An AMT Membership Teardown is sent to report an IGMP Membership Leave
or MLD Listener Done after a valid Response MAC has been received and
after the source address that was used to generate the Response MAC
is no longer available for sourcing packets.
An AMT Membership Teardown from the original source address and
source port is NOT valid and should be discarded if received. Use an
AMT Membership Update instead.
An AMT Membership Teardown can only contain either an IGMP Membership
Leave or an MLD Listener Done message. The encapsulated IGMP/MLD
message will have to be fabricated by the sender of the AMT
Membership Teardown in the case where there wasn't an original IGMP/
MLD message to be forwarded.
In order for the receiver to verify the Membership Teardown message,
it must contain the original source address and source port in
addition to the Original Request Nonce and Original Response MAC.
It is sent to the source address received in the original Query which
should be the same as the original Request.
The UDP destination port number should be the same one sent in the
original Request.
The relay is not required to use the IP source address of the IGMP
Membership Report for any particular purpose.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x7 | Reserved | Original Response MAC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original Response MAC (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original Request Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original Source Port | Source AFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Original Source Address |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IGMP Membership Leave or |
| MLD Listener Done (including IP header) |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AMT Membership Teardown
6.7.1. Type
The type of the message.
6.7.2. Reserved
A 8-bit reserved field. Sent as 0, ignored on receipt.
6.7.3. Original Response MAC
The 48-bit MAC received in the Membership Query and echoed back in
the Membership Update.
6.7.4. Original Request Nonce
A 32-bit identifier used to distinguish this request.
6.7.5. Original Source Port
The 16-bit port number used in the original AMT Membership update
that was used to generate the Original Response MAC.
6.7.6. Source AFI
A 16-bit Address Family Identifier (AFI) [RFC4760] used to determine
the protocol address family of the following Original Source Address.
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Presently defined values for the Address Family Identifier field are
specified in IANA's Address Family Numbers registry [IANA.AFN]
6.7.7. Original Source Address
The source address used in the original AMT Membership update that
was used to generate the Original Response MAC.
6.7.8. IGMP/MLD Message (including IP Header)
The message contains either an IGMP Membership Leave or an MLD
Listener Done. The IGMP or MLD version sent should be in response
the version of the query received in the original AMT Membership
Query. The IGMP/MLD Message includes a full IP Header.
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7. AMT Gateway Details
This section details the behavior of an AMT Gateway, which may be a
router serving an AMT site, or the site may consist of a single host,
serving as its own gateway.
7.1. At Startup Time
At startup time, the AMT gateway will bring up an AMT pseudo-
interface to be used for encapsulation. The gateway needs to
discover an AMT Relay to send Membership Requests. It can send an
AMT Relay Discovery at startup time or wait until it has a group
membership to report. The AMT Relay Discovery message is sent to the
AMT Relay Anycast Address. A unicast address (which is treated as a
link-layer address to the encapsulation interface) is received in the
AMT Relay Advertisement message. The discovery process SHOULD be
done periodically (e.g., once a day) to re-resolve the unicast
address of a close relay. To prevent startup synchronization, the
timer SHOULD use at least 10 percent jitter.
If the gateway is serving as a local router, it SHOULD also function
as an IGMP/MLD Proxy, as described in [RFC4605], with its IGMP/MLD
host-mode interface being the AMT pseudo-interface. This enables it
to translate group memberships on its downstream interfaces into
IGMP/MLD Reports. Hosts receiving multicast packets through an AMT
gateway acting as a proxy should ensure that their M-RIB accepts
multicast packets from the AMT gateway for the sources it is joining.
7.2. Gateway Group and Source Addresses
To support sourcing traffic to SSM groups by a gateway with a global
unicast address, the AMT Subnet Anycast Prefix is treated as the
subnet prefix of the AMT pseudo-interface, and an anycast address is
added on the interface. This anycast address is formed by
concatenating the AMT Subnet Anycast Prefix followed by the high bits
of the gateway's global unicast address.
The remaining bits of its global unicast address are appended to the
SSM prefix to create the group address and any spare bits may be
allocated using local policy.
If a gateway wants to source multicast traffic, it must select the
gateway source address and SSM group address in such a way that the
AMT relay can have enough information to reconstruct the gateway's
unicast address when it receives an SSM join for the source.
Note that multiple gateways might end up with the same anycast
address assigned to their pseudo-interfaces.
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7.2.1. IPv4
For example, if IANA assigns the IPv4 prefix x.y/16 as the AMT Subnet
Anycast Prefix, and the gateway has global unicast address a.b.c.d,
then the AMT Gateway's Anycast Source Address will be x.y.a.b. Since
the IPv4 SSM group range is 232/8, it MUST allocate IPv4 SSM groups
in the range 232.c.d/24.
Group:
8 16 8
+------------+------------------------+-------------+
| SSM prefix | Low 16 bits of | Local |
| 232/8 | real source address | Policy |
+------------+------------------------+-------------+
Source:
+-------------------------+-------------------------+
|16-bit AMT unicast prefix| high 16 bits of real src|
+-------------------------+-------------------------+
IPv4 format
This allows for 2^8 (256) IPv4 group addresses for use by each AMT
gateway.
7.2.2. IPv6
Similarly for IPv6, this is illustrated in the following figure.
Group:
32 64 32
+------------+------------------------+-------------+
| SSM prefix | Low 64 bits of | Local |
| FF3x::/32 | real source address | Policy |
+------------+------------------------+-------------+
Source:
+-------------------------+-------------------------+
|64-bit AMT unicast prefix| high 64 bits of real src|
+-------------------------+-------------------------+
IPv6 format
This allows for 2^32 (over 4 billion) IPv6 group addresses for use by
each AMT gateway.
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7.3. Joining Groups with MBone Sources
The IGMP/MLD protocol usually operates by having the Querier
multicast an IGMP/MLD Query message on the link. This behavior does
not work on NBMA links which do not support multicast. Since the set
of gateways is typically unknown to the relay (and potentially quite
large), unicasting the queries is also impractical. The following
behavior is used instead.
Applications residing in a gateway should join groups on the AMT
pseudo-interface, causing IGMP/MLD Membership/Listener Reports to be
sent over that interface. When UDP encapsulating the membership
reports (and in fact any other messages, unless specified otherwise
in this document), the destination address in the outer IP header is
the relay's unicast address. Robustness is provided by the
underlying IGMP/MLD protocol messages sent on the AMT pseudo-
interface. In other words, the gateway does not need to retransmit
IGMP/MLD Membership/Listener Reports and Leave/Done messages received
on the pseudo-interface since IGMP/MLD will already do this. The
gateway simply needs to encapsulate each IGMP/MLD Membership/Listener
Report and Leave/Done message it receives.
However, since periodic IGMP/MLD Membership/Listener Reports are sent
in response to IGMP/MLD Queries, a mechanism to trigger periodic
Membership/Listener Reports and Leave/Done messages is necessary.
The gateway should use a timer to trigger periodic AMT Membership
Updates.
If the gateway is behind a firewall device, the firewall may require
the gateway to periodically refresh the UDP state in the firewall at
a shorter interval than the standard IGMP/MLD Query interval. AMT
Requests can be sent periodically to solicit IGMP/MLD Queries. The
interval at which the AMT Requests are sent should be configurable to
ensure the firewall does not revert to blocking the UDP encapsulated
IP Multicast data packets. When the AMT Query is received, it can be
ignored unless it is time for a periodic AMT Membership Update.
The relay can use the Querier's Robustness Variable (QRV) defined in
[RFC3376] and [RFC3810] to adjust the number of Membership/Listener
Reports that are sent by the host joining the group.
7.4. Responding to Relay Changes
When a gateway determines that its current relay is unreachable
(e.g., upon receipt of an ICMP Unreachable message [RFC0792] for the
relay's unicast address), it may need to repeat relay address
discovery. However, care should be taken not to abandon the current
relay too quickly due to transient network conditions.
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7.5. Joining SSM Groups with AMT Gateway Sources
An IGMPv3/MLDv2 Report for a given (source, group) pair MAY be
encapsulated directly to the source, when the source address belongs
to the AMT Subnet Anycast Prefix.
The "link-layer" address to use as the destination address in the
outer IP header is obtained as follows. The source address in the
inclusion list of the IGMPv3/MLDv2 report will be an AMT Gateway
Anycast Address with the high bits of the address, and the remaining
bits will be in the middle of the group address.
Section 7.2 describes this format to recover the gateway source
address.
7.6. Receiving AMT Membership Updates by the Gateway
When an AMT Request is received by the gateway from another gateway
or relay, it follows the same 3-way handshake procedure a relay would
follow if it received the AMT Request. It generates a MAC and
responds with an AMT Membership Query. When the AMT Membership
Update is received, it verifies the MAC and then processes the IGMP/
MLD Membership/Listener Report or Leave/Done.
At the gateway, the IGMP/MLD packet should be an IGMPv3/MLDv2 source
specific (S,G) join or leave.
If S is not the AMT Gateway Anycast Address, the packet is silently
discarded. If G does not contain the low bits of the global unicast
address (as described above), the packet is also silently discarded.
The gateway adds the source address (from the outer IP header) and
UDP port of the report to a membership list for G. Maintaining this
membership list may be done in any implementation-dependent manner.
For example, it might be maintained by the "link-layer" inside the
AMT pseudo-interface, making it invisible to the normal IGMP/MLD
module.
7.7. Sending data to SSM groups
When multicast packets are sent on the AMT pseudo-interface, they are
encapsulated as follows. If the group address is not an SSM group,
then the packet is silently discarded (this memo does not currently
provide a way to send to non-SSM groups).
If the group address is an SSM group, then the packet is unicast
encapsulated to each remote node from which the gateway has received
an IGMPv3/MLDv2 report for the packet's (source, group) pair.
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8. Relay Router Details
8.1. At Startup time
At startup time, the relay router will bring up an NBMA-style AMT
pseudo-interface. It shall also add the AMT Relay Anycast Address on
some interface.
The relay router shall then advertise the AMT Relay Anycast Prefix
into the unicast-only Internet, as if it were a connection to an
external network. When the advertisement is done using BGP, the AS
path leading to the AMT Relay Anycast Prefix shall include the
identifier of the local AS.
The relay router shall also enable IGMPv3/MLDv2 on the AMT pseudo-
interface, except that it shall not multicast Queries (this might be
done, for example, by having the AMT pseudo-device drop them, or by
having the IGMP/MLD module not send them in the first place).
Finally, to support sourcing SSM traffic from AMT sites, the AMT
Subnet Anycast Prefix is assigned to the AMT pseudo-interface, and
the AMT Subnet Anycast Prefix is injected by the AMT Relay into the
M-RIB of MBGP.
8.2. Receiving Relay Discovery messages sent to the Anycast Address
When a relay receives an AMT Relay Discovery message directed to the
AMT Relay Anycast Address, it should respond with an AMT Relay
Advertisement containing its unicast address. The source and
destination addresses of the advertisement should be the same as the
destination and source addresses of the discovery message
respectively. Further, the nonce in the discovery message MUST be
copied into the advertisement message.
8.3. Receiving Membership Updates from AMT Gateways
The relay operates passively, sending no periodic IGMP/MLD Queries
but simply tracking membership information according to AMT Request/
Query/Membership Update tuples received. In addition, the relay must
also do explicit membership tracking, as to which gateways on the AMT
pseudo-interface have joined which groups. Once an AMT Membership
Update has been successfully received, it updates the forwarding
state for the appropriate group and source (if provided). When data
arrives for that group, the traffic must be encapsulated to each
gateway which has joined that group or (S,G).
The explicit membership tracking and unicast replication may be done
in any implementation-specific manner. Some examples are:
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1. The AMT pseudo-device driver might track the group information
and perform the replication at the "link-layer", with no changes
to a pre-existing IGMP/MLD module.
2. The IGMP/MLD module might have native support for explicit
membership tracking, especially if it supports other NBMA-style
interfaces.
If a relay wants to affect the rate at which the AMT Requests are
originated from a gateway, it can tune the membership timeout by
adjusting the Querier's Query Interval Code (QQIC) field in the IGMP/
MLD Query contained within the AMT Membership Query message. The
QQIC field is defined in [RFC3376] and [RFC3810]. However, since the
gateway may need to send AMT Requests frequently enough to prevent
firewall state from timing out, the relay may be limited in its
ability to spread out Requests coming from a gateway by adjusting the
QQIC field.
8.4. Receiving (S,G) Joins from the Native Side, for AMT Sources
The relay sends an IGMPv3/MLDv2 report to the AMT source as described
above in Section 5.1.2
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9. IANA Considerations
9.1. IPv4 and IPv6 Anycast Prefix Allocation
The IANA should allocate an IPv4 prefix and an IPv6 prefix dedicated
to the public AMT Relays to advertise to the native multicast
backbone. The prefix length should be determined by the IANA; the
prefix should be large enough to guarantee advertisement in the
default-free BGP networks.
9.1.1. IPv4
A prefix length of 16 will meet this requirement.
9.1.2. IPv6
A prefix length of 32 will meet this requirement. IANA has
previously set aside the range 2001::/16 for allocating prefixes for
this purpose.
9.2. IPv4 and IPv6 AMT Subnet Prefix Allocation
It should also be noted that this prefix length directly affects the
number of groups available to be created by the AMT gateway: in the
IPv4 case, a prefix length of 16 gives 256 groups, and a prefix
length of 8 gives 65536 groups.
All allocations are a one time effort and there will be no need for
any recurring assignment after this stage.
9.2.1. IPv4
As described above in Section 7.2.1 an IPv4 prefix with a length of
16 is requested for this purpose.
9.2.2. IPv6
As described above in Section 7.2.2 an IPv6 prefix with a length of
32 is requested.
9.3. UDP Port number
IANA has previously allocated UDP reserved port number 2268 for AMT
encapsulation.
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10. Security Considerations
The anycast technique introduces a risk that a rogue router or a
rogue AS could introduce a bogus route to the AMT Relay Anycast
prefix, and thus divert the traffic. Network managers have to
guarantee the integrity of their routing to the AMT Relay Anycast
prefix in much the same way that they guarantee the integrity of all
other routes.
Within the native MBGP infrastructure, there is a risk that a rogue
router or a rogue AS could inject a false route to the AMT Subnet
Anycast Prefix, and thus divert joins and cause RPF failures of
multicast traffic. As the AMT Subnet Anycast Prefix will be
advertised by multiple entities, guaranteeing the integrity of this
shared MBGP prefix is much more challenging than verifying the
correctness of a regular unicast advertisement. To mitigate this
threat, routing operators should configure the BGP sessions to filter
out any more specific advertisements for the AMT Subnet Anycast
Prefix.
Gateways and relays will accept and decapsulate multicast traffic
from any source from which regular unicast traffic is accepted. If
this is for any reason felt to be a security risk, then additional
source address based packet filtering MUST be applied:
1. To prevent a rogue sender (that can't do traditional spoofing
because of e.g. access lists deployed by its ISP) from making use
of AMT to send packets to an SSM tree, a relay that receives an
encapsulated multicast packet MUST discard the multicast packet
if the IP source address in the outer header does not match the
source address that would be extracted using the rules of
Section 7.2.
2. A gateway MUST discard encapsulated multicast packets if the
source address in the outer header is not the address to which
the encapsulated join message was sent. An AMT Gateway that
receives an encapsulated IGMPv3/MLDv2 (S,G)-Join MUST discard the
message if the IP destination address in the outer header does
not match the source address that would be extracted using the
rules of Section 7.2.
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11. Contributors
The following people provided significant contributions to earlier
versions of this draft.
Dirk Ooms
OneSparrow
Belegstraat 13; 2018 Antwerp; Belgium
EMail: dirk@onesparrow.com
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12. Acknowledgments
Most of the mechanisms described in this document are based on
similar work done by the NGTrans WG for obtaining automatic IPv6
connectivity without explicit tunnels ("6to4"). Tony Ballardie
provided helpful discussion that inspired this document.
In addition, extensive comments were received from Pekka Savola, Greg
Shepherd, Dino Farinacci, Toerless Eckert, Marshall Eubanks, John
Zwiebel, and Lenny Giuliano.
Juniper Networks was instrumental in funding several versions of this
draft as well as an open source implementation.
Greg Shepherd suggested the inclusion of the AMT Membership Teardown
message based on field experience.
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13. References
13.1. Normative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
13.2. Informative References
[IANA.AFN]
IANA, "Address Family Numbers", <http://www.iana.org/
assignments/address-family-numbers/
address-family-numbers.txt>.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.
[RFC1546] Partridge, C., Mendez, T., and W. Milliken, "Host
Anycasting Service", RFC 1546, November 1993.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3053] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
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[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, June 2001.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
January 2007.
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Authors' Addresses
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
USA
Phone: +1 425 703 8835
Email: dthaler@microsoft.com
Mohit Talwar
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
USA
Phone: +1 425 705 3131
Email: mohitt@microsoft.com
Amit Aggarwal
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
USA
Phone: +1 425 706 0593
Email: amitag@microsoft.com
Lorenzo Vicisano
Qualcomm Inc.
3165 Kifer Road
Santa Clara, CA 95051
USA
Email: vicisano@qualcomm.com
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Tom Pusateri
!j
2109 Mountain High Rd.
Wake Forest, NC 27587
USA
Email: pusateri@bangj.com
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