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Internet Engineering Task Force (IETF) P. Tarapore, Ed.
Request for Comments: 8313 R. Sayko
BCP: 213 AT&T
Category: Best Current Practice G. Shepherd
ISSN: 2070-1721 Cisco
T. Eckert, Ed.
Huawei
R. Krishnan
SupportVectors
December 2017
Use of Multicast across Inter-domain Peering Points
Abstract
This document examines the use of Source-Specific Multicast (SSM)
across inter-domain peering points for a specified set of deployment
scenarios. The objectives are to (1) describe the setup process for
multicast-based delivery across administrative domains for these
scenarios and (2) document supporting functionality to enable this
process.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8313.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Tarapore, et al. Best Current Practice [Page 1]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of Inter-domain Multicast Application Transport . . 5
3. Inter-domain Peering Point Requirements for Multicast . . . . 6
3.1. Native Multicast . . . . . . . . . . . . . . . . . . . . 6
3.2. Peering Point Enabled with GRE Tunnel . . . . . . . . . . 8
3.3. Peering Point Enabled with AMT - Both Domains Multicast
Enabled . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4. Peering Point Enabled with AMT - AD-2 Not Multicast
Enabled . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5. AD-2 Not Multicast Enabled - Multiple AMT Tunnels through
AD-2 . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4. Functional Guidelines . . . . . . . . . . . . . . . . . . . . 15
4.1. Network Interconnection Transport Guidelines . . . . . . 16
4.1.1. Bandwidth Management . . . . . . . . . . . . . . . . 16
4.2. Routing Aspects and Related Guidelines . . . . . . . . . 18
4.2.1. Native Multicast Routing Aspects . . . . . . . . . . 19
4.2.2. GRE Tunnel over Interconnecting Peering Point . . . . 19
4.2.3. Routing Aspects with AMT Tunnels . . . . . . . . . . 20
4.2.4. Public Peering Routing Aspects . . . . . . . . . . . 22
4.3. Back-Office Functions - Provisioning and Logging
Guidelines . . . . . . . . . . . . . . . . . . . . . . . 24
4.3.1. Provisioning Guidelines . . . . . . . . . . . . . . . 24
4.3.2. Inter-domain Authentication Guidelines . . . . . . . 25
4.3.3. Log-Management Guidelines . . . . . . . . . . . . . . 26
4.4. Operations - Service Performance and Monitoring
Guidelines . . . . . . . . . . . . . . . . . . . . . . . 27
4.5. Client Reliability Models / Service Assurance Guidelines 29
4.6. Application Accounting Guidelines . . . . . . . . . . . . 29
5. Troubleshooting and Diagnostics . . . . . . . . . . . . . . . 30
6. Security Considerations . . . . . . . . . . . . . . . . . . . 31
6.1. DoS Attacks (against State and Bandwidth) . . . . . . . . 31
6.2. Content Security . . . . . . . . . . . . . . . . . . . . 32
6.3. Peering Encryption . . . . . . . . . . . . . . . . . . . 34
6.4. Operational Aspects . . . . . . . . . . . . . . . . . . . 35
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 36
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.1. Normative References . . . . . . . . . . . . . . . . . . 37
9.2. Informative References . . . . . . . . . . . . . . . . . 39
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40
Tarapore, et al. Best Current Practice [Page 2]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
1. Introduction
Content and data from several types of applications (e.g., live video
streaming, software downloads) are well suited for delivery via
multicast means. The use of multicast for delivering such content or
other data offers significant savings in terms of utilization of
resources in any given administrative domain. End User (EU) demand
for such content or other data is growing. Often, this requires
transporting the content or other data across administrative domains
via inter-domain peering points.
The objectives of this document are twofold:
o Describe the technical process and establish guidelines for
setting up multicast-based delivery of application content or
other data across inter-domain peering points via a set of
use cases (where "Use Case 3.1" corresponds to Section 3.1,
"Use Case 3.2" corresponds to Section 3.2, etc.).
o Catalog all required exchanges of information between the
administrative domains to support multicast-based delivery. This
enables operators to initiate necessary processes to support
inter-domain peering with multicast.
The scope and assumptions for this document are as follows:
o Administrative Domain 1 (AD-1) sources content to one or more EUs
in one or more Administrative Domain 2 (AD-2) entities. AD-1 and
AD-2 want to use IP multicast to allow support for large and
growing EU populations, with a minimum amount of duplicated
traffic to send across network links.
* This document does not detail the case where EUs are
originating content. To support that additional service, it is
recommended that some method (outside the scope of this
document) be used by which the content from EUs is transmitted
to the application in AD-1 and AD-1 can send out the traffic as
IP multicast. From that point on, the descriptions in this
document apply, except that they are not complete because they
do not cover the transport or operational aspects of the leg
from the EU to AD-1.
* This document does not detail the case where AD-1 and AD-2 are
not directly connected to each other and are instead connected
via one or more other ADs (as opposed to a peering point) that
serve as transit providers. The cases described in this
document where tunnels are used between AD-1 and AD-2 can be
applied to such scenarios, but SLA ("Service Level Agreement")
Tarapore, et al. Best Current Practice [Page 3]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
control, for example, would be different. Additional issues
will likely exist as well in such scenarios. This topic is
left for further study.
o For the purposes of this document, the term "peering point" refers
to a network connection ("link") between two administrative
network domains over which traffic is exchanged between them.
This is also referred to as a Network-to-Network Interface (NNI).
Unless otherwise noted, it is assumed that the peering point is a
private peering point, where the network connection is a
physically or virtually isolated network connection solely between
AD-1 and AD-2. The other case is that of a broadcast peering
point, which is a common option in public Internet Exchange Points
(IXPs). See Section 4.2.4 for more details.
o AD-1 is enabled with native multicast. A peering point exists
between AD-1 and AD-2.
o It is understood that several protocols are available for this
purpose, including Protocol-Independent Multicast - Sparse Mode
(PIM-SM) and Protocol-Independent Multicast - Source-Specific
Multicast (PIM-SSM) [RFC7761], the Internet Group Management
Protocol (IGMP) [RFC3376], and Multicast Listener Discovery (MLD)
[RFC3810].
o As described in Section 2, the source IP address of the (so-called
"(S,G)") multicast stream in the originating AD (AD-1) is known.
Under this condition, using PIM-SSM is beneficial, as it allows
the receiver's upstream router to send a join message directly to
the source without the need to invoke an intermediate Rendezvous
Point (RP). The use of SSM also presents an improved threat
mitigation profile against attack, as described in [RFC4609].
Hence, in the case of inter-domain peering, it is recommended that
only SSM protocols be used; the setup of inter-domain peering for
ASM (Any-Source Multicast) is out of scope for this document.
o The rest of this document assumes that PIM-SSM and BGP are used
across the peering point, plus Automatic Multicast Tunneling (AMT)
[RFC7450] and/or Generic Routing Encapsulation (GRE), according to
the scenario in question. The use of other protocols is beyond
the scope of this document.
o AMT is set up at the peering point if either the peering point or
AD-2 is not multicast enabled. It is assumed that an AMT relay
will be available to a client for multicast delivery. The
selection of an optimal AMT relay by a client is out of scope for
this document. Note that using AMT is necessary only when native
Tarapore, et al. Best Current Practice [Page 4]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
multicast is unavailable in the peering point (Use Case 3.3) or in
the downstream administrative domain (Use Cases 3.4 and 3.5).
o It is assumed that the collection of billing data is done at the
application level and is not considered to be a networking issue.
The settlements process for EU billing and/or inter-provider
billing is out of scope for this document.
o Inter-domain network connectivity troubleshooting is only
considered within the context of a cooperative process between the
two domains.
This document also attempts to identify ways by which the peering
process can be improved. Development of new methods for improvement
is beyond the scope of this document.
2. Overview of Inter-domain Multicast Application Transport
A multicast-based application delivery scenario is as follows:
o Two independent administrative domains are interconnected via a
peering point.
o The peering point is either multicast enabled (end-to-end native
multicast across the two domains) or connected by one of two
possible tunnel types:
* A GRE tunnel [RFC2784] allowing multicast tunneling across the
peering point, or
* AMT [RFC7450].
o A service provider controls one or more application sources in
AD-1 that will send multicast IP packets via one or more (S,G)s
(multicast traffic flows; see Section 4.2.1 if you are unfamiliar
with IP multicast). It is assumed that the service being provided
is suitable for delivery via multicast (e.g., live video streaming
of popular events, software downloads to many devices) and that
the packet streams will be carried by a suitable multicast
transport protocol.
o An EU controls a device connected to AD-2, which runs an
application client compatible with the service provider's
application source.
o The application client joins appropriate (S,G)s in order to
receive the data necessary to provide the service to the EU. The
mechanisms by which the application client learns the appropriate
Tarapore, et al. Best Current Practice [Page 5]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
(S,G)s are an implementation detail of the application and are out
of scope for this document.
The assumption here is that AD-1 has ultimate responsibility for
delivering the multicast-based service on behalf of the content
source(s). All relevant interactions between the two domains
described in this document are based on this assumption.
Note that AD-2 may be an independent network domain (e.g., a Tier 1
network operator domain). Alternately, AD-2 could also be an
enterprise network domain operated by a single customer of AD-1. The
peering point architecture and requirements may have some unique
aspects associated with enterprise networks; see Section 3.
The use cases describing various architectural configurations for
multicast distribution, along with associated requirements, are
described in Section 3. Section 4 contains a comprehensive list of
pertinent information that needs to be exchanged between the two
domains in order to support functions to enable application
transport.
3. Inter-domain Peering Point Requirements for Multicast
The transport of applications using multicast requires that the
inter-domain peering point be enabled to support such a process.
This section presents five use cases for consideration.
3.1. Native Multicast
This use case involves end-to-end native multicast between the two
administrative domains, and the peering point is also native
multicast enabled. See Figure 1.
Tarapore, et al. Best Current Practice [Page 6]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ | | |
| | | +------+ | | +------+ | +----+
| | AS |------>| BR |-|---------|->| BR |-------------|-->| EU |
| | | +------+ | I1 | +------+ |I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
AD = Administrative Domain (independent autonomous system)
AS = multicast (e.g., content) Application Source
BR = Border Router
I1 = AD-1 and AD-2 multicast interconnection (e.g., MP-BGP)
I2 = AD-2 and EU multicast connection
Figure 1: Content Distribution via End-to-End Native Multicast
Advantages of this configuration:
o Most efficient use of bandwidth in both domains.
o Fewer devices in the path traversed by the multicast stream when
compared to an AMT-enabled peering point.
From the perspective of AD-1, the one disadvantage associated with
native multicast to AD-2 instead of individual unicast to every EU in
AD-2 is that it does not have the ability to count the number of EUs
as well as the transmitted bytes delivered to them. This information
is relevant from the perspective of customer billing and operational
logs. It is assumed that such data will be collected by the
application layer. The application-layer mechanisms for generating
this information need to be robust enough so that all pertinent
requirements for the source provider and the AD operator are
satisfactorily met. The specifics of these methods are beyond the
scope of this document.
Architectural guidelines for this configuration are as follows:
a. Dual homing for peering points between domains is recommended as
a way to ensure reliability with full BGP table visibility.
b. If the peering point between AD-1 and AD-2 is a controlled
network environment, then bandwidth can be allocated accordingly
by the two domains to permit the transit of non-rate-adaptive
Tarapore, et al. Best Current Practice [Page 7]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
multicast traffic. If this is not the case, then the multicast
traffic must support congestion control via any of the mechanisms
described in Section 4.1 of [BCP145].
c. The sending and receiving of multicast traffic between two
domains is typically determined by local policies associated with
each domain. For example, if AD-1 is a service provider and AD-2
is an enterprise, then AD-1 may support local policies for
traffic delivery to, but not traffic reception from, AD-2.
Another example is the use of a policy by which AD-1 delivers
specified content to AD-2 only if such delivery has been accepted
by contract.
d. It is assumed that relevant information on multicast streams
delivered to EUs in AD-2 is collected by available capabilities
in the application layer. The precise nature and formats of the
collected information will be determined by directives from the
source owner and the domain operators.
3.2. Peering Point Enabled with GRE Tunnel
The peering point is not native multicast enabled in this use case.
There is a GRE tunnel provisioned over the peering point. See
Figure 2.
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ +---+ | (I1) | +---+ |
| | | +--+ |uBR|-|--------|-|uBR| +--+ | +----+
| | AS |-->|BR| +---+-| | +---+ |BR| -------->|-->| EU |
| | | +--+<........|........|........>+--+ |I2 +----+
\ +----+ / I1 \ /
\ / GRE \ /
\ / Tunnel \ /
------------------- -------------------
AD = Administrative Domain (independent autonomous system)
AS = multicast (e.g., content) Application Source
uBR = unicast Border Router - not necessarily multicast enabled;
may be the same router as BR
BR = Border Router - for multicast
I1 = AD-1 and AD-2 multicast interconnection (e.g., MP-BGP)
I2 = AD-2 and EU multicast connection
Figure 2: Content Distribution via GRE Tunnel
Tarapore, et al. Best Current Practice [Page 8]
RFC 8313 Multicast for Inter-domain Peering Points December 2017
In this case, interconnection I1 between AD-1 and AD-2 in Figure 2 is
multicast enabled via a GRE tunnel [RFC2784] between the two BRs and
encapsulating the multicast protocols across it.
Normally, this approach is chosen if the uBR physically connected to
the peering link cannot or should not be enabled for IP multicast.
This approach may also be beneficial if the BR and uBR are the same
device but the peering link is a broadcast domain (IXP); see
Section 4.2.4.
The routing configuration is basically unchanged: instead of running
BGP (SAFI-2) ("SAFI" stands for "Subsequent Address Family
Identifier") across the native IP multicast link between AD-1 and
AD-2, BGP (SAFI-2) is now run across the GRE tunnel.
Advantages of this configuration:
o Highly efficient use of bandwidth in both domains, although not as
efficient as the fully native multicast use case (Section 3.1).
o Fewer devices in the path traversed by the multicast stream when
compared to an AMT-enabled peering point.
o Ability to support partial and/or incremental IP multicast
deployments in AD-1 and/or AD-2: only the path or paths between
the AS/BR (AD-1) and the BR/EU (AD-2) need to be multicast
enabled. The uBRs may not support IP multicast or enabling it
could be seen as operationally risky on that important edge node,
whereas dedicated BR nodes for IP multicast may (at least
initially) be more acceptable. The BR can also be located such
that only parts of the domain may need to support native IP
multicast (e.g., only the core in AD-1 but not edge networks
towards the uBR).
o GRE is an existing technology and is relatively simple to
implement.
Disadvantages of this configuration:
o Per Use Case 3.1, current router technology cannot count the
number of EUs or the number of bytes transmitted.
o The GRE tunnel requires manual configuration.
o The GRE tunnel must be established prior to starting the stream.
o The GRE tunnel is often left pinned up.
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RFC 8313 Multicast for Inter-domain Peering Points December 2017
Architectural guidelines for this configuration include the
following:
Guidelines (a) through (d) are the same as those described in
Use Case 3.1. Two additional guidelines are as follows:
e. GRE tunnels are typically configured manually between peering
points to support multicast delivery between domains.
f. It is recommended that the GRE tunnel (tunnel server)
configuration in the source network be such that it only
advertises the routes to the application sources and not to the
entire network. This practice will prevent unauthorized delivery
of applications through the tunnel (for example, if the
application (e.g., content) is not part of an agreed-upon
inter-domain partnership).
3.3. Peering Point Enabled with AMT - Both Domains Multicast Enabled
It is assumed that both administrative domains in this use case are
native multicast enabled here; however, the peering point is not.
The peering point is enabled with AMT. The basic configuration is
depicted in Figure 3.
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ +---+ | I1 | +---+ |
| | | +--+ |uBR|-|--------|-|uBR| +--+ | +----+
| | AS |-->|AR| +---+-| | +---+ |AG| -------->|-->| EU |
| | | +--+<........|........|........>+--+ |I2 +----+
\ +----+ / AMT \ /
\ / Tunnel \ /
\ / \ /
------------------- -------------------
AD = Administrative Domain (independent autonomous system)
AS = multicast (e.g., content) Application Source
AR = AMT Relay
AG = AMT Gateway
uBR = unicast Border Router - not multicast enabled;
also, either AR = uBR (AD-1) or uBR = AG (AD-2)
I1 = AMT interconnection between AD-1 and AD-2
I2 = AD-2 and EU multicast connection
Figure 3: AMT Interconnection between AD-1 and AD-2
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Advantages of this configuration:
o Highly efficient use of bandwidth in AD-1.
o AMT is an existing technology and is relatively simple to
implement. Attractive properties of AMT include the following:
* Dynamic interconnection between the gateway-relay pair across
the peering point.
* Ability to serve clients and servers with differing policies.
Disadvantages of this configuration:
o Per Use Case 3.1 (AD-2 is native multicast), current router
technology cannot count the number of EUs or the number of bytes
transmitted to all EUs.
o Additional devices (AMT gateway and relay pairs) may be introduced
into the path if these services are not incorporated into the
existing routing nodes.
o Currently undefined mechanisms for the AG to automatically select
the optimal AR.
Architectural guidelines for this configuration are as follows:
Guidelines (a) through (d) are the same as those described in
Use Case 3.1. In addition,
e. It is recommended that AMT relay and gateway pairs be configured
at the peering points to support multicast delivery between
domains. AMT tunnels will then configure dynamically across the
peering points once the gateway in AD-2 receives the (S,G)
information from the EU.
3.4. Peering Point Enabled with AMT - AD-2 Not Multicast Enabled
In this AMT use case, AD-2 is not multicast enabled. Hence, the
interconnection between AD-2 and the EU is also not multicast
enabled. This use case is depicted in Figure 4.
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RFC 8313 Multicast for Inter-domain Peering Points December 2017
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Not Multicast \
/ \ / Enabled) \ N(large)
| +----+ +---+ | | +---+ | # EUs
| | | +--+ |uBR|-|--------|-|uBR| | +----+
| | AS |-->|AR| +---+-| | +---+ ................>|EU/G|
| | | +--+<........|........|........... |I2 +----+
\ +----+ / N x AMT\ /
\ / Tunnel \ /
\ / \ /
------------------- -------------------
AS = multicast (e.g., content) Application Source
uBR = unicast Border Router - not multicast enabled;
otherwise, AR = uBR (in AD-1)
AR = AMT Relay
EU/G = Gateway client embedded in EU device
I2 = AMT tunnel connecting EU/G to AR in AD-1 through
non-multicast-enabled AD-2
Figure 4: AMT Tunnel Connecting AD-1 AMT Relay and EU Gateway
This use case is equivalent to having unicast distribution of the
application through AD-2. The total number of AMT tunnels would be
equal to the total number of EUs requesting the application. The
peering point thus needs to accommodate the total number of AMT
tunnels between the two domains. Each AMT tunnel can provide the
data usage associated with each EU.
Advantages of this configuration:
o Efficient use of bandwidth in AD-1 (the closer the AR is to the
uBR, the more efficient).
o Ability of AD-1 to introduce content delivery based on IP
multicast, without any support by network devices in AD-2: only
the application side in the EU device needs to perform AMT gateway
library functionality to receive traffic from the AMT relay.
o Allows AD-2 to "upgrade" to Use Case 3.5 (see Section 3.5) at a
later time, without any change in AD-1 at that time.
o AMT is an existing technology and is relatively simple to
implement. Attractive properties of AMT include the following:
* Dynamic interconnection between the AMT gateway-relay pair
across the peering point.
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RFC 8313 Multicast for Inter-domain Peering Points December 2017
* Ability to serve clients and servers with differing policies.
o Each AMT tunnel serves as a count for each EU and is also able to
track data usage (bytes) delivered to the EU.
Disadvantages of this configuration:
o Additional devices (AMT gateway and relay pairs) are introduced
into the transport path.
o Assuming multiple peering points between the domains, the EU
gateway needs to be able to find the "correct" AMT relay in AD-1.
Architectural guidelines for this configuration are as follows:
Guidelines (a) through (c) are the same as those described in
Use Case 3.1. In addition,
d. It is necessary that proper procedures be implemented such that
the AMT gateway at the EU device is able to find the correct AMT
relay for each (S,G) content stream. Standard mechanisms for
that selection are still subject to ongoing work. This includes
the use of anycast gateway addresses, anycast DNS names, or
explicit configuration that maps (S,G) to a relay address; or
letting the application in the EU/G provide the relay address to
the embedded AMT gateway function.
e. The AMT tunnel's capabilities are expected to be sufficient for
the purpose of collecting relevant information on the multicast
streams delivered to EUs in AD-2.
3.5. AD-2 Not Multicast Enabled - Multiple AMT Tunnels through AD-2
Figure 5 illustrates a variation of Use Case 3.4:
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RFC 8313 Multicast for Inter-domain Peering Points December 2017
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Not Multicast \
/ +---+ \ (I1) / +---+ Enabled) \
| +----+ |uBR|-|--------|-|uBR| |
| | | +--+ +---+ | | +---+ +---+ | +----+
| | AS |-->|AR|<........|.... | +---+ |AG/|....>|EU/G|
| | | +--+ | ......|.|AG/|..........>|AR2| |I3 +----+
\ +----+ / I1 \ |AR1| I2 +---+ /
\ / Single \+---+ /
\ / AMT Tunnel \ /
------------------- -------------------
uBR = unicast Border Router - not multicast enabled;
also, either AR = uBR (AD-1) or uBR = AGAR1 (AD-2)
AS = multicast (e.g., content) Application Source
AR = AMT Relay in AD-1
AGAR1 = AMT Gateway/Relay node in AD-2 across peering point
I1 = AMT tunnel connecting AR in AD-1 to gateway in AGAR1 in AD-2
AGAR2 = AMT Gateway/Relay node at AD-2 network edge
I2 = AMT tunnel connecting relay in AGAR1 to gateway in AGAR2
EU/G = Gateway client embedded in EU device
I3 = AMT tunnel connecting EU/G to AR in AGAR2
Figure 5: AMT Tunnel Connecting AMT Gateways and Relays
Use Case 3.4 results in several long AMT tunnels crossing the entire
network of AD-2 linking the EU device and the AMT relay in AD-1
through the peering point. Depending on the number of EUs, there is
a likelihood of an unacceptably high amount of traffic due to the
large number of AMT tunnels -- and unicast streams -- through the
peering point. This situation can be alleviated as follows:
o Provisioning of strategically located AMT nodes in AD-2. An
AMT node comprises co-location of an AMT gateway and an AMT relay.
No change is required by AD-1, as compared to Use Case 3.4. This
can be done whenever AD-2 sees fit (e.g., too much traffic across
the peering point).
o One such node is on the AD-2 side of the peering point (AMT node
AGAR1 in Figure 5).
o A single AMT tunnel established across the peering point linking
the AMT relay in AD-1 to the AMT gateway in AMT node AGAR1
in AD-2.
o AMT tunnels linking AMT node AGAR1 at the peering point in AD-2 to
other AMT nodes located at the edges of AD-2: e.g., AMT tunnel I2
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linking the AMT relay in AGAR1 to the AMT gateway in AMT
node AGAR2 (Figure 5).
o AMT tunnels linking an EU device (via a gateway client embedded in
the device) and an AMT relay in an appropriate AMT node at the
edge of AD-2: e.g., I3 linking the EU gateway in the device to the
AMT relay in AMT node AGAR2.
o In the simplest option (not shown), AD-2 only deploys a single
AGAR1 node and lets the EU/G build AMT tunnels directly to it.
This setup already solves the problem of replicated traffic across
the peering point. As soon as there is a need to support more AMT
tunnels to the EU/G, then additional AGAR2 nodes can be deployed
by AD-2.
The advantage of such a chained set of AMT tunnels is that the total
number of unicast streams across AD-2 is significantly reduced, thus
freeing up bandwidth. Additionally, there will be a single unicast
stream across the peering point instead of, possibly, an unacceptably
large number of such streams per Use Case 3.4. However, this implies
that several AMT tunnels will need to be dynamically configured by
the various AMT gateways, based solely on the (S,G) information
received from the application client at the EU device. A suitable
mechanism for such dynamic configurations is therefore critical.
Architectural guidelines for this configuration are as follows:
Guidelines (a) through (c) are the same as those described in
Use Case 3.1. In addition,
d. It is necessary that proper procedures be implemented such that
the various AMT gateways (at the EU devices and the AMT nodes in
AD-2) are able to find the correct AMT relay in other AMT nodes
as appropriate. Standard mechanisms for that selection are still
subject to ongoing work. This includes the use of anycast
gateway addresses, anycast DNS names, or explicit configuration
that maps (S,G) to a relay address. On the EU/G, this mapping
information may come from the application.
e. The AMT tunnel's capabilities are expected to be sufficient for
the purpose of collecting relevant information on the multicast
streams delivered to EUs in AD-2.
4. Functional Guidelines
Supporting functions and related interfaces over the peering point
that enable the multicast transport of the application are listed in
this section. Critical information parameters that need to be
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exchanged in support of these functions are enumerated, along with
guidelines as appropriate. Specific interface functions for
consideration are as follows.
4.1. Network Interconnection Transport Guidelines
The term "network interconnection transport" refers to the
interconnection points between the two administrative domains. The
following is a representative set of attributes that the two
administrative domains will need to agree on to support multicast
delivery.
o Number of peering points.
o Peering point addresses and locations.
o Connection type - Dedicated for multicast delivery or shared with
other services.
o Connection mode - Direct connectivity between the two ADs or via
another ISP.
o Peering point protocol support - Multicast protocols that will be
used for multicast delivery will need to be supported at these
points. Examples of such protocols include External BGP (EBGP)
[RFC4760] peering via MP-BGP (Multiprotocol BGP) SAFI-2 [RFC4760].
o Bandwidth allocation - If shared with other services, then there
needs to be a determination of the share of bandwidth reserved for
multicast delivery. See Section 4.1.1 below for more details.
o QoS requirements - Delay and/or latency specifications that need
to be specified in an SLA.
o AD roles and responsibilities - The role played by each AD for
provisioning and maintaining the set of peering points to support
multicast delivery.
4.1.1. Bandwidth Management
Like IP unicast traffic, IP multicast traffic carried across
non-controlled networks must comply with congestion control
principles as described in [BCP41] and as explained in detail for UDP
IP multicast in [BCP145].
Non-controlled networks (such as the Internet) are networks where
there is no policy for managing bandwidth other than best effort with
a fair share of bandwidth under congestion. As a simplified rule of
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thumb, complying with congestion control principles means reducing
bandwidth under congestion in a way that is fair to competing
(typically TCP) flows ("rate adaptive").
In many instances, multicast content delivery evolves from
intra-domain deployments where it is handled as a controlled network
service and does not comply with congestion control principles. It
was given a reserved amount of bandwidth and admitted to the network
so that congestion never occurs. Therefore, the congestion control
issue should be given specific attention when evolving to an
inter-domain peering deployment.
In the case where end-to-end IP multicast traffic passes across the
network of two ADs (and their subsidiaries/customers), both ADs must
agree on a consistent traffic-management policy. If, for example,
AD-1 sources non-congestion-aware IP multicast traffic and AD-2
carries it as best-effort traffic across links shared with other
Internet traffic (subject to congestion), this will not work: under
congestion, some amount of that traffic will be dropped, often
rendering the remaining packets as undecodable garbage clogging up
the network in AD-2; because this traffic is not congestion aware,
the loss does not reduce this rate. Competing traffic will not get
their fair share under congestion, and EUs will be frustrated by the
extremely bad quality of both their IP multicast traffic and other
(e.g., TCP) traffic. Note that this is not an IP multicast
technology issue but is solely a transport-layer / application-layer
issue: the problem would just as likely happen if AD-1 were to send
non-rate-adaptive unicast traffic -- for example, legacy IPTV
video-on-demand traffic, which is typically also non-congestion
aware. Note that because rate adaptation in IP unicast video is
commonplace today due to the availability of ABR (Adaptive Bitrate)
video, it is very unlikely that this will happen in reality with IP
unicast.
While the rules for traffic management apply whether IP multicast is
tunneled or not, the one feature that can make AMT tunnels more
difficult is the unpredictability of bandwidth requirements across
underlying links because of the way they can be used: with native IP
multicast or GRE tunnels, the amount of bandwidth depends on the
amount of content -- not the number of EUs -- and is therefore easier
to plan for. AMT tunnels terminating in the EU/G, on the other hand,
scale with the number of EUs. In the vicinity of the AMT relay, they
can introduce a very large amount of replicated traffic, and it is
not always feasible to provision enough bandwidth for all possible
EUs to get the highest quality for all their content during peak
utilization in such setups -- unless the AMT relays are very close to
the EU edge. Therefore, it is also recommended that IP multicast
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rate adaptation be used, even inside controlled networks, when using
AMT tunnels directly to the EU/G.
Note that rate-adaptive IP multicast traffic in general does not mean
that the sender is reducing the bitrate but rather that the EUs that
experience congestion are joining to a lower-bitrate (S,G) stream of
the content, similar to ABR streaming over TCP. Therefore, migration
from a non-rate-adaptive bitrate to a rate-adaptive bitrate in IP
multicast will also change the dynamic (S,G) join behavior in the
network, resulting in potentially higher performance requirements for
IP multicast protocols (IGMP/PIM), especially on the last hops where
dynamic changes occur (including AMT gateways/relays): in non-rate-
adaptive IP multicast, only "channel change" causes state change, but
in rate-adaptive multicast, congestion also causes state change.
Even though not fully specified in this document, peerings that rely
on GRE/AMT tunnels may be across one or more transit ADs instead of
an exclusive (non-shared, L1/L2) path. Unless those transit ADs are
explicitly contracted to provide other than "best effort" transit for
the tunneled traffic, the tunneled IP multicast traffic must be
rate adaptive in order to not violate BCP 41 across those
transit ADs.
4.2. Routing Aspects and Related Guidelines
The main objective for multicast delivery routing is to ensure that
the EU receives the multicast stream from the "most optimal" source
[INF_ATIS_10], which typically:
o Maximizes the multicast portion of the transport and minimizes any
unicast portion of the delivery, and
o Minimizes the overall combined route distance of the network(s).
This routing objective applies to both native multicast and AMT; the
actual methodology of the solution will be different for each.
Regardless, the routing solution is expected to:
o Be scalable,
o Avoid or minimize new protocol development or modifications, and