Internet DRAFT - draft-ietf-mboned-interdomain-peering-bcp
draft-ietf-mboned-interdomain-peering-bcp
MBONED Working Group P. Tarapore, Ed.
Internet-Draft R. Sayko
Intended status: Best Current Practice AT&T
Expires: May 3, 2018 G. Shepherd
Cisco
T. Eckert, Ed.
Huawei
R. Krishnan
SupportVectors
October 30, 2017
Use of Multicast Across Inter-Domain Peering Points
draft-ietf-mboned-interdomain-peering-bcp-14
Abstract
This document examines the use of Source Specific Multicast (SSM)
across inter-domain peering points for a specified set of deployment
scenarios. The objective is to describe the setup process for
multicast-based delivery across administrative domains for these
scenarios and document supporting functionality to enable this
process.
Status of This Memo
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This Internet-Draft will expire on May 3, 2018.
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
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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 . . . . . . . . . . . . . . . . . . . . 7
3.2. Peering Point Enabled with GRE Tunnel . . . . . . . . . . 8
3.3. Peering Point Enabled with an AMT - Both Domains
Multicast Enabled . . . . . . . . . . . . . . . . . . . . 10
3.4. Peering Point Enabled with an AMT - AD-2 Not Multicast
Enabled . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. AD-2 Not Multicast Enabled - Multiple AMT Tunnels Through
AD-2 . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4. Functional Guidelines . . . . . . . . . . . . . . . . . . . . 16
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 . . . . . . . . . . . . . . . . . . . . . . . 23
4.3.1. Provisioning Guidelines . . . . . . . . . . . . . . . 24
4.3.2. Interdomain 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 . . . . . . . . . . . . . . . 29
6. Security Considerations . . . . . . . . . . . . . . . . . . . 30
6.1. DoS attacks (against state and bandwidth) . . . . . . . . 30
6.2. Content Security . . . . . . . . . . . . . . . . . . . . 32
6.3. Peering Encryption . . . . . . . . . . . . . . . . . . . 34
6.4. Operational Aspects . . . . . . . . . . . . . . . . . . . 34
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 35
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
10. Change log [RFC Editor: Please remove] . . . . . . . . . . . 37
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11. References . . . . . . . . . . . . . . . . . . . . . . . . . 39
11.1. Normative References . . . . . . . . . . . . . . . . . . 39
11.2. Informative References . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
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 of utilization of resources in
any given administrative domain. End user 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 objective of this Best Current Practices document is 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.
o Catalog all required information exchange 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 End
Users (EUs) in one or more Administrative Domain 2 (AD-2). AD-1
and AD-2 want to use IP multicast to allow supporting large and
growing EU populations with minimum amount of duplicated traffic
to send across network links.
o This document does not detail the case where EUs are
originating content. To support that additional service, it is
recommended to use some method (outside the scope of this
document) by which the content from EUs is transmitted to the
application in AD-1 that this document refers to as the
multicast source and let it 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 EU to AD-1.
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o This document does not detail the case where AD-1 and AD-2 are
not directly connected to each other but only via one or more
AD-3 (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") control for
example would be different. Other additional issues will
likely exist as well in such scenarios. This is for further
study.
o For the purpose 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, the peering point is assumed to be 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
(IXP). See Section 4.2.2 for more details about that option.
o Administrative Domain 1 (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 PIM-SM and Protocol Independent Multicast -
Source Specific Multicast (PIM-SSM) [RFC7761], Internet Group
Management Protocol (IGMP) [RFC3376], and Multicast Listener
Discovery (MLD) [RFC3810].
o As described in Section 2, the source IP address of the multicast
stream in the originating AD (AD-1) is known. Under this
condition, PIM-SSM use is beneficial as it allows the receiver's
upstream router to directly send a JOIN message to the source
without the need of invoking an intermediate Rendezvous Point
(RP). 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 to use only SSM
protocols; the setup of inter- domain peering for ASM (Any-Source
Multicast) is not in scope for this document.
o The rest of the document assumes that PIM-SSM and BGP are used
across the peering point plus AMT and/or GRE according to
scenario. The use of other protocols is beyond the scope of this
document.
o An Automatic Multicast Tunnel (AMT) [RFC7450] is setup 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
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client for multicast delivery. The selection of an optimal AMT
relay by a client is out of scope for this document. Note that
AMT use is necessary only when native 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 The collection of billing data is assumed to be done at the
application level and is not considered to be a networking issue.
The settlements process for end user 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 it is connected by one of two
possible tunnel types:
o A Generic Routing Encapsulation (GRE) Tunnel [RFC2784] allowing
multicast tunneling across the peering point, or
o An Automatic Multicast Tunnel (AMT) [RFC7450].
o A service provider controls one or more application sources in
AD-1 which 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, etc.), and
that the packet streams will carried by a suitable multicast
transport protocol.
o An End User (EU) controls a device connected to AD-2, which runs
an application client compatible with the service provider's
application source.
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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
(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 domain 2 may be an independent network domain (e.g.: Tier 1
network operator domain). Alternately, domain 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 the Enterprise case.
The Use Cases describing various architectural configurations for the
multicast distribution along with associated requirements is
described in section 3. Unique aspects related to the Enterprise
network possibility will be described in this section. 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 the application transport.
Note that domain 2 may be an independent network domain (e.g., Tier 1
network operator domain). Alternately, domain 2 could also be an
Enterprise network domain operated by a single customer.
The Use Cases describing various architectural configurations for the
multicast distribution along with associated requirements is
described in Section 3. The peering point architecture and
requirements may have some unique aspects associated with the
Enterprise case. These unique aspects will also be 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 the application transport.
3. Inter-domain Peering Point Requirements for Multicast
The transport of applications using multicast requires that the
inter-domain peering point is enabled to support such a process.
There are five Use Cases for consideration in this document.
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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.
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Multicast Enabled) \
/ \ / \
| +----+ | | |
| | | +------+ | | +------+ | +----+
| | AS |------>| BR |-|---------|->| BR |-------------|-->| EU |
| | | +------+ | I1 | +------+ |I2 +----+
\ +----+ / \ /
\ / \ /
\ / \ /
------------------- -------------------
AD = Administrative Domain (Independent Autonomous System)
AS = Application (e.g., Content) Multicast Source
BR = Border Router
I1 = AD-1 and AD-2 Multicast Interconnection (e.g., MBGP)
I2 = AD-2 and EU Multicast Connection
Figure 1: Content Distribution via End to End Native Multicast
Advantages of this configuration are:
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 into 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
End Users 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 such 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:
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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
multicast traffic. If this is not the case, then the multicast
traffic must support rate-adaption (see [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. Relevant information on multicast streams delivered to End Users
in AD-2 is assumed to be 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 Generic Routing Encapsulation Tunnel provisioned over the
peering point. See Figure 2.
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------------------- -------------------
/ 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 = Application (e.g., Content) Multicast 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., MBGP)
I2 = AD-2 and EU Multicast Connection
Figure 2: Content Distribution via GRE Tunnel
In this case, the interconnection I1 between AD-1 and AD-2 in
Figure 2 is multicast enabled via a Generic Routing Encapsulation
Tunnel (GRE) [RFC2784] between the two BR and encapsulating the
multicast protocols across it.
Normally, this approach is choosen if the uBR physcially connected to
the peering link can or should not be enabled for IP multicast. This
approach may also be beneficial if BR and uBR are the same device,
but the peering link is a broadcast domain (IXP), see Figure 6.
The routing configuration is basically unchanged: Instead of BGP
(SAFI2) across the native IP multicast link between AD-1 and AD-2,
BGP (SAFI2) 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.
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(s) between AS/BR
(AD-1) and BR/EU (AD-2) need to be multicast enabled. The uBRs
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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 be more acceptable at least
initially. 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 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 end users or the number bytes transmitted.
o GRE tunnel requires manual configuration.
o The GRE must be established prior to stream starting.
o The GRE tunnel is often left pinned up.
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 is 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 (e.g., if application - e.g.,
content - is not part of an agreed inter-domain partnership).
3.3. Peering Point Enabled with an AMT - Both Domains Multicast Enabled
Both administrative domains in this Use Case are assumed to be native
multicast enabled here; however, the peering point is not.
The peering point is enabled with an Automatic Multicast Tunnel. The
basic configuration is depicted in Figure 2.
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------------------- -------------------
/ 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 = Application (e.g., Content) Multicast Source
AR = AMT Relay
AG = AMT Gateway
uBR = unicast Border Router - not multicast enabled
otherwise AR=uBR (AD-1), 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
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:
o Dynamic interconnection between Gateway-Relay pair across the
peering point.
o 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 end users or the number of
bytes transmitted to all end users.
o Additional devices (AMT Gateway and Relay pairs) may be introduced
into the path if these services are not incorporated in the
existing routing nodes.
o Currently undefined mechanisms for the AG to automatically select
the optimal AR.
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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 an AMT - AD-2 Not Multicast Enabled
In this AMT Use Case, the second administrative domain AD-2 is not
multicast enabled. Hence, the interconnection between AD-2 and the
End User is also not multicast enabled. This Use Case is depicted in
Figure 3.
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Non Multicast \
/ \ / Enabled) \ N(large)
| +----+ +---+ | | +---+ | #EU
| | | +--+ |uBR|-|--------|-|uBR| | +----+
| | AS |-->|AR| +---+-| | +---+ ................>|EU/G|
| | | +--+ <.......|........|........... |I2 +----+
\ +----+ / N x AMT\ /
\ / Tunnel \ /
\ / \ /
------------------- -------------------
AS = Application Multicast 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 End Users 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 End User.
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Advantages of this configuration:
o Efficient use of bandwidth in AD-1 (The closer AR is to uBR, the
more efficient).
o Ability for AD-1 to introduce IP multicast based content delivery
without any support by network devices in AD-2: Only application
side in the EU device needs to perform AMT gateway library
functionality to receive traffic from AMT relay.
o Allows for AD-2 to "upgrade" to Use Case 3.5 (see below) 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:
o Dynamic interconnection between Gateway-Relay pair across the
peering point.
o Ability to serve clients and servers with differing policies.
o Each AMT tunnel serves as a count for each End User 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.
d. It is necessary that proper procedures are implemented such that
the AMT Gateway at the End User 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
use of anycast gateway addresses, anycast DNS names, explicit
configuration that is mapping (S,G) to a relay address or letting
the application in the EU/G provide the relay address to the
embedded AMT gateway function.
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e. The AMT tunnel capabilities are expected to be sufficient for the
purpose of collecting relevant information on the multicast
streams delivered to End Users in AD-2.
3.5. AD-2 Not Multicast Enabled - Multiple AMT Tunnels Through AD-2
This is a variation of Use Case 3.4 as follows:
------------------- -------------------
/ AD-1 \ / AD-2 \
/ (Multicast Enabled) \ / (Non 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
otherwise AR=uBR (AD-1) or ubr=AGAR1 (AD-2)
AS = 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 GW in AGAR1 in AD-2
AGAR2 = AMT Gateway/Relay node at AD-2 Network Edge
I2 = AMT Tunnel Connecting Relay in AGAR1 to GW 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 Relay 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 End Users,
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 AD-2. An
AMT node comprises co-location of an AMT Gateway and an AMT Relay.
No change is required by AD-1 compared to 3.4. This can be done
whenever AD-2 seems fit (too much traffic across peering point.
o One such node is at the AD-2 side of the peering point (node AGAR1
in above Figure).
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o Single AMT tunnel established across peering point linking AMT
Relay in AD-1 to the AMT Gateway in the AMT node AGAR1 in AD-2.
o AMT tunnels linking AMT node AGAR1 at peering point in AD-2 to
other AMT nodes located at the edges of AD-2: e.g., AMT tunnel I2
linking AMT Relay in AGAR1 to AMT Gateway in AMT node AGAR2 in
Figure 4.
o AMT tunnels linking EU device (via Gateway client embedded in
device) and AMT Relay in appropriate AMT node at edge of AD-2:
e.g., I3 linking EU Gateway in device to AMT Relay in AMT node
AGAR2.
o In the most simple option (not shown), AD-2 only deploys a single
AGAR1 and lets 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 need to support more AMT
tunnels to EU/G, then additional AGAR2 nodes can be deployed by
AD-2.
The advantage for 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.
d. It is necessary that proper procedures are implemented such that
the various AMT Gateways (at the End User 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 use of anycast
gateway addresses, anycast DNS names, or explicit configuration
that is mapping (S,G) to a relay address. On the EU/G, this
mapping information may come from the application.
e. The AMT tunnel capabilities are expected to be sufficient for the
purpose of collecting relevant information on the multicast
streams delivered to End Users in AD-2.
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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
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 will need to be
agreed to between the two administrative domains 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 AD's 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 protocols include eBGP [RFC4760] and MBGP
[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 to Congestion Control Principles as
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described in [BCP41] and explained in detail for UDP IP multicast in
[BCP145].
Non-controlled networks (such as the Internet) are those where there
is no policy for managing bandwidth other than best effort with fair
share of bandwidth under congestion. As a simplified rule of thumb,
complying to congestion control principles means to reduce bandwidth
under congestion in a way that is fair to competing competing
(typically TCP) flow ("rate adaptive").
In many instances, multicast content delivery evolves from intra-
domain deployments where it is handled as a controlled network
service and of not complyng to 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 interdomain
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 and subject to congestion, this will not work: Under
congestion, some amount of that traffic will be dropped, rendering
the remaining packets often as undecodeable garbage clogging up the
network in AD-2 and because this 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 frusted by extremely bad
quality of both their IP multicast and other (e.g.: TCP) traffic.
Note that this is not an IP multicast technology issue, but solely a
transport/application layer issue: The problem would equally happen
if AD-1 would send non-rate adaptive unicast traffic,, for example
legacy IPTV video-on-demand traffic which typically is also non
congestion aware. Because rate adaption in IP unicast video is
commonplace today because of ABR (Adaptive Bitrate Video), it is very
unlikely for this to happen though in reality with IP unicast.
While the rules for traffic management apply whether or not 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 EU/G
on the other hand scale with the number of EUs. In the vicinity of
the AMT relay they can introduce very large amount of replicated
traffic and it is not always feasible to provision enough bandwidth
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for all possible EU 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 to use
IP multicast rate adaptation even inside controlled networks when
using AMT tunnels directly to 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 adaptive bitrate streaming over TCP.
Migration from non rate-adaptive to rate adaptive bitrate in IP
multicast does therefore also change the dynamic (S,G) join behavior
in the network resulting in potentially higher performance
requirement for IP multicast protocols (IGMP/PIM), especially on the
last hops where dynamic changes occur (including AMT gateway/relays):
In non rate-adaptive IP multicast, only "channel change" causes state
change, in rate-adaptive also the congestion situation 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 IP multicast traffic tunneled must be rate
adaptive to not violate BCP41 across those transit ADs.
4.2. Routing Aspects and Related Guidelines
The main objective for multicast delivery routing is to ensure that
the End User 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 network(s) route distance.
This routing objective applies to both Native and AMT; the actual
methodology of the solution will be different for each. Regardless,
the routing solution is expected:
o To be scalable,
o To avoid or minimize new protocol development or modifications,
and
o To be robust enough to achieve high reliability and automatically
adjust to changes and problems in the multicast infrastructure.
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For both Native and AMT environments, having a source as close as
possible to the EU network is most desirable; therefore, in some
cases, an AD may prefer to have multiple sources near different
peering points. However, that is entirely an implementation issue.
4.2.1. Native Multicast Routing Aspects
Native multicast simply requires that the Administrative Domains
coordinate and advertise the correct source address(es) at their
network interconnection peering points(i.e., border routers). An
example of multicast delivery via a Native Multicast process across
two Administrative Domains is as follows assuming that the
interconnecting peering points are also multicast enabled:
o Appropriate information is obtained by the EU client who is a
subscriber to AD-2 (see Use Case 3.1). This information is in the
form of metadata and it contains instructions directing the EU
client to launch an appropriate application if necessary, as well
as additional information for the application about the source
location and the group (or stream) id in the form of the "S,G"
data. The "S" portion provides the name or IP address of the
source of the multicast stream. The metadata may also contain
alternate delivery information such as specifying the unicast
address of the stream.
o The client uses the join message with S,G to join the multicast
stream [RFC4604]. To facilitate this process, the two AD's need
to do the following:
o Advertise the source id(s) over the Peering Points.
o Exchange relevant Peering Point information such as Capacity
and Utilization.
o Implement compatible multicast protocols to ensure proper
multicast delivery across the peering points.
4.2.2. GRE Tunnel over Interconnecting Peering Point
If the interconnecting peering point is not multicast enabled and
both AD's are multicast enabled, then a simple solution is to
provision a GRE tunnel between the two AD's - see Use Case 3.2.2.
The termination points of the tunnel will usually be a network
engineering decision, but generally will be between the border
routers or even between the AD 2 border router and the AD 1 source
(or source access router). The GRE tunnel would allow end-to-end
native multicast or AMT multicast to traverse the interface.
Coordination and advertisement of the source IP is still required.
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The two AD's need to follow the same process as described in 4.2.1 to
facilitate multicast delivery across the Peering Points.
4.2.3. Routing Aspects with AMT Tunnels
Unlike Native Multicast (with or without GRE), an AMT Multicast
environment is more complex. It presents a dual layered problem
because there are two criteria that should be simultaneously met:
o Find the closest AMT relay to the end-user that also has multicast
connectivity to the content source, and
o Minimize the AMT unicast tunnel distance.
There are essentially two components to the AMT specification
AMT Relays: These serve the purpose of tunneling UDP multicast
traffic to the receivers (i.e., End-Points). The AMT Relay will
receive the traffic natively from the multicast media source and
will replicate the stream on behalf of the downstream AMT
Gateways, encapsulating the multicast packets into unicast packets
and sending them over the tunnel toward the AMT Gateway. In
addition, the AMT Relay may perform various usage and activity
statistics collection. This results in moving the replication
point closer to the end user, and cuts down on traffic across the
network. Thus, the linear costs of adding unicast subscribers can
be avoided. However, unicast replication is still required for
each requesting End-Point within the unicast-only network.
AMT Gateway (GW): The Gateway will reside on an End-Point - this
could be any type of IP host such as a Personal Computer (PC),
mobile phone, Set Top Box (STB) or appliances. The AMT Gateway
receives join and leave requests from the Application via an
Application Programming Interface (API). In this manner, the
Gateway allows the End-Point to conduct itself as a true Multicast
End-Point. The AMT Gateway will encapsulate AMT messages into UDP
packets and send them through a tunnel (across the unicast-only
infrastructure) to the AMT Relay.
The simplest AMT Use Case (section 3.3) involves peering points that
are not multicast enabled between two multicast enabled AD's. An AMT
tunnel is deployed between an AMT Relay on the AD 1 side of the
peering point and an AMT Gateway on the AD 2 side of the peering
point. One advantage to this arrangement is that the tunnel is
established on an as needed basis and need not be a provisioned
element. The two AD's can coordinate and advertise special AMT Relay
Anycast addresses with each other. Alternately, they may decide to
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simply provision Relay addresses, though this would not be an optimal
solution in terms of scalability.
Use Cases 3.4 and 3.5 describe more complicated AMT situations as
AD-2 is not multicast enabled. For these cases, the End User device
needs to be able to setup an AMT tunnel in the most optimal manner.
There are many methods by which relay selection can be done including
the use of DNS based queries and static lookup tables [RFC7450]. The
choice of the method is implementation dependent and is up to the
network operators. Comparison of various methods is out of scope for
this document; it is for further study.
An illustrative example of a relay selection based on DNS queries and
Anycast IP addresses process for Use Cases 3.4 and 3.5 is described
here. Using an Anycast IP address for AMT Relays allows for all AMT
Gateways to find the "closest" AMT Relay - the nearest edge of the
multicast topology of the source. Note that this is strictly
illustrative; the choice of the method is up to the network
operators. The basic process is as follows:
o Appropriate metadata is obtained by the EU client application.
The metadata contains instructions directing the EU client to an
ordered list of particular destinations to seek the requested
stream and, for multicast, specifies the source location and the
group (or stream) ID in the form of the "S,G" data. The "S"
portion provides the URI (name or IP address) of the source of the
multicast stream and the "G" identifies the particular stream
originated by that source. The metadata may also contain
alternate delivery information such as the address of the unicast
form of the content to be used, for example, if the multicast
stream becomes unavailable.
o Using the information from the metadata, and possibly information
provisioned directly in the EU client, a DNS query is initiated in
order to connect the EU client/AMT Gateway to an AMT Relay.
o Query results are obtained, and may return an Anycast address or a
specific unicast address of a relay. Multiple relays will
typically exist. The Anycast address is a routable "pseudo-
address" shared among the relays that can gain multicast access to
the source.
o If a specific IP address unique to a relay was not obtained, the
AMT Gateway then sends a message (e.g., the discovery message) to
the Anycast address such that the network is making the routing
choice of particular relay - e.g., closest relay to the EU.
Details are outside the scope for this document. See [RFC4786].
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o The contacted AMT Relay then returns its specific unicast IP
address (after which the Anycast address is no longer required).
Variations may exist as well.
o The AMT Gateway uses that unicast IP address to initiate a three-
way handshake with the AMT Relay.
o AMT Gateway provides "S,G" to the AMT Relay (embedded in AMT
protocol messages).
o AMT Relay receives the "S,G" information and uses the S,G to join
the appropriate multicast stream, if it has not already subscribed
to that stream.
o AMT Relay encapsulates the multicast stream into the tunnel
between the Relay and the Gateway, providing the requested content
to the EU.
4.2.4. Public Peering Routing Aspects
AD-1a AD-1b
BR BR
| |
--+-+---------------+-+-- broadcast peering point LAN
| |
BR BR
AD-2a AD-2b
Figure 6: Broadcast Peering Point
A broadcast peering point is an L2 subnet connecting 3 or more ADs.
It is common in IXPs and usually consists of ethernet switch(es)
operated by the IXP connecting to BRs operated by the ADs.
In an example setup domain AD-2a peers with AD-1a and wants to
receive IP multicast from it. Likewise AD-2b peers with AD-1b and
wants to receive IP multicast from it.
Assume one or more IP multicast (S,G) traffic streams can be served
by both AD-1a and AD-1b, for example because both AD-1a and AD-1b do
contract this content from the same content source.
In this case, AD-2a and AD-2b can not control anymore which upstream
domain, AD-1a or AD-1b will forward this (S,G) into the LAN. AD-2a
BR requests the (S,G) from AD-1a BR and AD-2b BR requests the same
(S,G) from AD-1b BR. To avoid duplicate packets, an (S,G) can be
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forwarded by only one router onto the LAN, and PIM-SM/PIM-SSM detects
requests for duplicate transmission and resolve it via the so-called
"assert" protocol operation which results in only one BR forwarding
the traffic. Assume this is AD-1a BR. AD-2b will then receive the
multicast traffic unexpectedly from a provider with whom it does not
have a mutual agreement for the traffic. Quality issues in EUs
behind AD-2b caused by AD-1a will cause a lot of responsiblity and
troubleshooting issues.
In face of this technical issues, we describe the following options
how IP multicast can be carried across broadcast peering point LANs:
1. IP multicast is tunneled across the LAN. Any of the GRE/AMT
tunneling solutions mentioned in this document are applicable.
This is the one case where specifically a GRE tunnel between the
upstream BR (e.g.: AD-1a) and downstream BR (e.g.: AD-2a) is
recommended as opposed to tunneling across uBRs which are not the
actual BRs.
2. The LAN has only one upstream AD that is sourcing IP multicast
and native IP multicast is used. This is an efficient way to
distribute the same IP multicast content to multiple downstream
ADs. Misbehaving downstream BRs can still disrupt the delivery
of IP multicast from the upstream BR to other downstream BRs,
therefore strict rules must be follow to prohibit that case. The
downstream BRs must ensure that they will always consider only
the upstream BR as a source for multicast traffic: e.g.: no BGP
SAFI-2 peerings between the downstream ADs across the peering
point LAN, so that only the upstream BR is the only possible
next-hop reachable across this LAN. And routing policies
configured to avoid fall back to the use of SAFI-1 (unicast)
routes for IP multicast if unicast BGP peering is not limited in
the same way.
3. The LAN has multiple upstreams, but they are federated and agree
on a consistent policy for IP multicast traffic across the LAN.
One policy is that each possible source is only announced by one
upstream BR. Another policy is that sources are redundantly
announced (problematic case mentioned in above example), but the
upstream domains also provide mutual operational insight to help
troubleshooting (outside the scope of this document).
4.3. Back Office Functions - Provisioning and Logging Guidelines
Back Office refers to the following:
o Servers and Content Management systems that support the delivery
of applications via multicast and interactions between AD's.
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o Functionality associated with logging, reporting, ordering,
provisioning, maintenance, service assurance, settlement, etc.
4.3.1. Provisioning Guidelines
Resources for basic connectivity between AD's Providers need to be
provisioned as follows:
o Sufficient capacity must be provisioned to support multicast-based
delivery across AD's.
o Sufficient capacity must be provisioned for connectivity between
all supporting back-offices of the AD's as appropriate. This
includes activating proper security treatment for these back-
office connections (gateways, firewalls, etc) as appropriate.
o Routing protocols as needed, e.g. configuring routers to support
these.
Provisioning aspects related to Multicast-Based inter-domain delivery
are as follows.
The ability to receive requested application via multicast is
triggered via receipt of the necessary metadata. Hence, this
metadata must be provided to the EU regarding multicast URL - and
unicast fallback if applicable. AD-2 must enable the delivery of
this metadata to the EU and provision appropriate resources for this
purpose.
Native multicast functionality is assumed to be available across many
ISP backbones, peering and access networks. If, however, native
multicast is not an option (Use Cases 3.4 and 3.5), then:
o EU must have multicast client to use AMT multicast obtained either
from Application Source (per agreement with AD-1) or from AD-1 or
AD-2 (if delegated by the Application Source).
o If provided by AD-1/AD-2, then the EU could be redirected to a
client download site (note: this could be an Application Source
site). If provided by the Application Source, then this Source
would have to coordinate with AD-1 to ensure the proper client is
provided (assuming multiple possible clients).
o Where AMT Gateways support different application sets, all AD-2
AMT Relays need to be provisioned with all source & group
addresses for streams it is allowed to join.
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o DNS across each AD must be provisioned to enable a client GW to
locate the optimal AMT Relay (i.e. longest multicast path and
shortest unicast tunnel) with connectivity to the content's
multicast source.
Provisioning Aspects Related to Operations and Customer Care are
stated as follows.
Each AD provider is assumed to provision operations and customer care
access to their own systems.
AD-1's operations and customer care functions must have visibility to
what is happening in AD-2's network or to the service provided by AD-
2, sufficient to verify their mutual goals and operations, e.g. to
know how the EU's are being served. This can be done in two ways:
o Automated interfaces are built between AD-1 and AD-2 such that
operations and customer care continue using their own systems.
This requires coordination between the two AD's with appropriate
provisioning of necessary resources.
o AD-1's operations and customer care personnel are provided access
directly to AD-2's system. In this scenario, additional
provisioning in these systems will be needed to provide necessary
access. Additional provisioning must be agreed to by the two AD's
to support this option.
4.3.2. Interdomain Authentication Guidelines
All interactions between pairs of AD's can be discovered and/or be
associated with the account(s) utilized for delivered applications.
Supporting guidelines are as follows:
o A unique identifier is recommended to designate each master
account.
o AD-2 is expected to set up "accounts" (logical facility generally
protected by credentials such as login passwords) for use by AD-1.
Multiple accounts and multiple types or partitions of accounts can
apply, e.g. customer accounts, security accounts, etc.
The reason to specifically mention the need for AD-1 to initiate
interactions with AD-2 (and use some account for that), as opposed to
the opposite direction is based on the recommended workflow initiated
by customers (see Section 4.4): The customer contacts content source
(part of AD-1), when AD-1 sees the need to propagate the issue, it
will interact with AD-2 using the aforementioned guidelines.
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4.3.3. Log Management Guidelines
Successful delivery (in terms of user experience) of applications or
content via multicast between pairs of interconnecting AD's can be
improved through the ability to exchange appropriate logs for various
workflows - troubleshooting, accounting and billing, traffic and
content transmission optimization, content and application
development optimization and so on.
The basic model as explained in before is that the content source and
on its behalf AD-1 take over primary responsibility for customer
experience and the AD-2's support this. The application/content
owner is the only participant who has and needs full insight into the
application level and can map the customer application experience to
the network traffic flows - which it then with the help of AD-2 or
logs from AD-2 can analyze and interpret.
The main difference between unicast delivery and multicast delivery
is that the content source can infer a lot more about downstream
network problems from a unicasted stream than from a multicasted
stream: The multicasted stream is not per-EU except after the last
replication, which is in most cases not in AD-1. Logs from the
application, including the receiver side at the EU, can provide
insight, but can not help to fully isolate network problems because
of the IP multicast per-application operational state built across
AD-1 and AD-2 (aka: the (S,G) state and any other feature operational
state such as DiffServ QoS).
See Section 7 for more discussions about the privacy considerations
of the model described here.
Different type of logs are known to help support operations in AD-1
when provided by AD-2. This could be done as part of AD-1/AD-2
contracts. Note that except for implied multicast specific elements,
the options listed here are not unique or novel for IP multicast, but
they are more important for services novel to the operators than for
operationally well established services (such as unicast). Therefore
we detail them as follows:
o Usage information logs at aggregate level.
o Usage failure instances at an aggregate level.
o Grouped or sequenced application access. performance, behavior
and failure at an aggregate level to support potential Application
Provider-driven strategies. Examples of aggregate levels include
grouped video clips, web pages, and sets of software download.
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o Security logs, aggregated or summarized according to agreement
(with additional detail potentially provided during security
events, by agreement).
o Access logs (EU), when needed for troubleshooting.
o Application logs (what is the application doing), when needed for
shared troubleshooting.
o Syslogs (network management), when needed for shared
troubleshooting.
The two AD's may supply additional security logs to each other as
agreed to by contract(s). Examples include the following:
o Information related to general security-relevant activity which
may be of use from a protective or response perspective, such as
types and counts of attacks detected, related source information,
related target information, etc.
o Aggregated or summarized logs according to agreement (with
additional detail potentially provided during security events, by
agreement).
4.4. Operations - Service Performance and Monitoring Guidelines
Service Performance refers to monitoring metrics related to multicast
delivery via probes. The focus is on the service provided by AD-2 to
AD-1 on behalf of all multicast application sources (metrics may be
specified for SLA use or otherwise). Associated guidelines are as
follows:
o Both AD's are expected to monitor, collect, and analyze service
performance metrics for multicast applications. AD-2 provides
relevant performance information to AD-1; this enables AD-1 to
create an end-to-end performance view on behalf of the multicast
application source.
o Both AD's are expected to agree on the type of probes to be used
to monitor multicast delivery performance. For example, AD-2 may
permit AD-1's probes to be utilized in the AD-2 multicast service
footprint. Alternately, AD-2 may deploy its own probes and relay
performance information back to AD-1.
Service Monitoring generally refers to a service (as a whole)
provided on behalf of a particular multicast application source
provider. It thus involves complaints from End Users when service
problems occur. EUs direct their complaints to the source provider;
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in turn the source provider submits these complaints to AD-1. The
responsibility for service delivery lies with AD-1; as such AD-1 will
need to determine where the service problem is occurring - its own
network or in AD-2. It is expected that each AD will have tools to
monitor multicast service status in its own network.
o Both AD's will determine how best to deploy multicast service
monitoring tools. Typically, each AD will deploy its own set of
monitoring tools; in which case, both AD's are expected to inform
each other when multicast delivery problems are detected.
o AD-2 may experience some problems in its network. For example,
for the AMT Use Cases, one or more AMT Relays may be experiencing
difficulties. AD-2 may be able to fix the problem by rerouting
the multicast streams via alternate AMT Relays. If the fix is not
successful and multicast service delivery degrades, then AD-2
needs to report the issue to AD-1.
o When problem notification is received from a multicast application
source, AD-1 determines whether the cause of the problem is within
its own network or within the AD-2 domain. If the cause is within
the AD-2 domain, then AD-1 supplies all necessary information to
AD-2. Examples of supporting information include the following:
o Kind of problem(s).
o Starting point & duration of problem(s).
o Conditions in which problem(s) occur.
o IP address blocks of affected users.
o ISPs of affected users.
o Type of access e.g., mobile versus desktop.
o Network locations of affected EUs.
o Both AD's conduct some form of root cause analysis for multicast
service delivery problems. Examples of various factors for
consideration include:
o Verification that the service configuration matches the product
features.
o Correlation and consolidation of the various customer problems
and resource troubles into a single root service problem.
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o Prioritization of currently open service problems, giving
consideration to problem impact, service level agreement, etc.
o Conduction of service tests, including one time tests or a
series of tests over a period of time.
o Analysis of test results.
o Analysis of relevant network fault or performance data.
o Analysis of the problem information provided by the customer
(CP).
o Once the cause of the problem has been determined and the problem
has been fixed, both AD's need to work jointly to verify and
validate the success of the fix.
4.5. Client Reliability Models/Service Assurance Guidelines
There are multiple options for instituting reliability architectures,
most are at the application level. Both AD's should work those out
with their contract or agreement and with the multicast application
source providers.
Network reliability can also be enhanced by the two AD's by
provisioning alternate delivery mechanisms via unicast means.
4.6. Application Accounting Guidelines
Application level accounting needs to be handled differently in the
application than in IP unicast because the source side does not
directly deliver packets to individual receivers. Instead, this
needs to be signalled back by the receiver to the source.
For network transport diagnostics, AD-1 and AD-2 should have
mechanisms in place to ensure proper accounting for the volume of
bytes delivered through the peering point and separately the number
of bytes delivered to EUs.
5. Troubleshooting and Diagnostics
Any service provider supporting multicast delivery of content should
have the capability to collect diagnostics as part of multicast
troubleshooting practices and resolve network issues accordingly.
Issues may become apparent or identified either through network
monitoring functions or by customer reported problems as described in
section 4.4.
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It is recommended that multicast diagnostics will be performed
leveraging established operational practices such as those documented
in [MDH-04]. However, given that inter-domain multicast creates a
significant interdependence of proper networking functionality
between providers there does exist a need for providers to be able to
signal (or otherwise alert) each other if there are any issues noted
by either one.
Service providers may also wish to allow limited read-only
administrative access to their routers to their AD peers for
troubleshooting. Of specific interest are access to active
troubleshooting tools especially [Traceroute] and
[I-D.ietf-mboned-mtrace-v2].
Another option is to include this functionality into the IP multicast
receiver application on the EU device and allow for these diagnostics
to be remotely used by support operations. Note though that AMT does
not allow to pass traceroute or mtrace requests, therefore
troubleshooting in the presence of AMT does not work as well end-to-
end as it can with native (or even GRE encapsulated) IP multicast,
especially wrt. to traceroute and mtrace. Instead, troubleshooting
directly on the actual network devices is then more likely necessary.
The specifics of the notification and alerts are beyond the scope of
this document, but general guidelines are similar to those described
in section 4.4 (Service Performance and Monitoring). Some general
communications issues are stated as follows.
o Appropriate communications channels will be established between
the customer service and operations groups from both AD's to
facilitate information sharing related to diagnostic
troubleshooting.
o A default resolution period may be considered to resolve open
issues. Alternately, mutually acceptable resolution periods could
be established depending on the severity of the identified
trouble.
6. Security Considerations
6.1. DoS attacks (against state and bandwidth)
Reliable operations of IP multicast requires some basic protection
against DoS (Denial of Service) attacks.
SSM IP multicast is self protecting against attacks from illicit
sources. Their traffic will not be forwarded beyond the first hop
router because that would require (S,G) memership reports from
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receiver. Traffic from sources will only be forwarded from the valid
source because RPF ("Reverse Path Forwarding") is part of the
protocols. One can say that [BCP38] style protection against spoofed
source traffic is therefore built into PIM-SM/PIM-SSM.
Receivers can attack SSM IP multicast by originating such (S,G)
membership reports. This can result in a DoS attack against state
through the creation of a large number of (S,G) states that create
high control plane load or even inhibit later creation of valid
(S,G). In conjunction with collaborating illicit sources it can also
result in illicit sources traffic being forwarded.
Today, these type of attacks are usually mitigated by explicitly
defining the set of permissible (S,G) on e.g.: the last hop routers
in replicating IP multicast to EUs; For example via (S,G) Access
Control Lists applied to IGMP/MLD membership state creation. Each AD
is expected to prohibit (S,G) state creation for invalid sources
inside their own AD.
In the peering case, AD-2 is without further information not aware of
the set of valid (S,G) from AD-1, so this set needs to be
communicated via operational procedures from AD-1 to AD-2 to provide
protection against this type of DoS attacks. Future work could
signal this information in an automated way: BGP extensions, DNS
Resource Records or backend automation between AD-1 and AD-2.
Backend automation is the short term most viable solution because it
does not require router software extensions like the other two.
Observation of traffic flowing via (S,G) state could also be used to
automate recognition of invalid (S,G) state created by receivers in
the absence of explicit information from AD-1.
The second DoS attack through (S,G) membership reports is when
receivers create too much valid (S,G) state to attack bandwidth
available to other EU. Consider the uplink into a last-hop-router
connecting to 100 EU. If one EU joins to more multicast content than
what fits into this link, then this would impact also the quality of
the same content for the other 99 EU. If traffic is not rate
adaptive, the effects are even worse.
The mitigation is the same as what is often employed for unicast:
Policing of per-EU total amont of traffic. Unlike unicast though,
this can not be done anywhere along the path (e.g.: on an arbitrary
bottleneck link), but it has to happen at the point of last
replication to the different EU. Simple solutions such as limiting
the maximum number of joined (S,G) per EU are readily available,
solutions that consider bandwidth consumed exist as vendor specific
feature in routers. Note that this is primarily a non-peering issue
in AD-2, it only becomes a peering issue if the peering-link itself
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is not big enough to carry all possible content from AD-1 or in case
3.4 where the AMT relay in AD-1 is that last replication point.
Limiting the amount of (S,G) state per EU is also a good first
measure to prohibit too much undesired "empty" state to be built
(state not carrying traffic), but it would not suffice in case of
DDoS attack - viruses that impact a large number of EU devices.
6.2. Content Security
Content confidentiality, DRM (Digital Restrictions Management),
authentication and authorization are optional based on the content
delivered. For content that is "FTA" (Free To Air), the following
considerations can be ignored and content can be sent unencrypted and
without EU authentication and authorization. Note though that the
mechanisms described here may also be desireable by the application
source to better track users even if the content itself would not
require it.
For interdomain content, there are at least two models for content
confidentiality, DRM and end-user authentication and authorization:
In the classical (IP)TV model, responsibility is per-domain and
content is and can be passed on unencrypted. AD-1 delivers content
to AD-2, AD-2 can further process the content including features like
ad-insertion and AD-2 is the sole point of contact regarding the
contact for its EUs. In this document, we do not consider this case
because it typically involves higher than network layer service
aspects operated by AD-2 and this document focusses on the network
layer AD-1/AD-2 peering case, but not the application layer peering
case. Nevertheless, this model can be derived through additional
work from what is describe here.
The other case is the one in which content confidentiality, DRM, end-
user authentication and authorization are end-to-end:
responsibilities of the multicast application source provider and
receiver application. This is the model assumed here. It is also
the model used in Internet OTT video delivery. We discuss the
threads incurred in this model due to the use of IP multicast in AD-
1/AD-2 and across the peering.
End-to-end encryption enables end-to-end EU authentication and
authorization: The EU may be able to IGMP/MLD join and receive the
content, but it can only decrypt it when it receives the decryption
key from the content source in AD-1. The key is the authorization.
Keeping that key to itself and prohibiting playout of the decrypted
content to non-copy-protected interfaces are typical DRM features in
that receiver application or EU device operating system.
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End-to-end ecnryption is continuously attacked. Keys may be subject
to brute force attack so that content can be decrypted potentially
later, or keys are extracted from the EU application/device and
shared with other unauthenticated receivers. One important class of
content is where the value is in live consumption, such as sports or
other event (concert) streaming. Extraction of keying material from
compromised authenticated EU and sharing with unauthenticated EU is
not sufficient. It is also necessary for those unauthenticated EUs
to get a streaming copy of the content itself. In unicast streaming,
they can not get such a copy from the content source (because they
can not authenticate) and because of asymmetric bandwidths, it is
often impossible to get the content from compromised EUs to large
number of unauthenticated EUs. EUs behind classical 16 Mbps down, 1
Mbps up ADSL links are the best example. With increasing broadband
access speeds unicast peer-to-peer copying of content becomes easier,
but it likely will always be easily detectable by the ADs because of
its traffic patterns and volume.
When IP multicast is being used without additionals security, AD-2 is
not aware which EU is authenticated for which content. Any
unauthenticated EU in AD-2 could therefore get a copy of the
encrypted content without suspicion by AD-2 or AD-1 and either live-
deode it in the presence of compromised authenticated EU and key
sharing, or later decrypt it in the presence of federated brute force
key cracking.
To mitigate this issue, the last replication point that is creating
(S,G) copies to EUs would need to permit those copies only after
authentication of EUs. This would establish the same authenticated
EU only copy deliver thast is used in unicast.
Schemes for per EU IP multicast authentication/authorization (and in
result non-delivery/copying of per-content IP multicast traffic) have
been built in the past and are deployed in service providers for
intradomain IPTV services, but no standard exist for this. For
example, there is no standardized radius attribute for authenticating
the IGMP/MLD filter set, but implementations of this exist. The
authors are specifically also not aware of schemes where the same
authentication credentials used to get the encryption key from the
content source could also be used to authenticate and authorize the
network layer IP multicast replication for the content. Such schemes
are technically not difficult to build and would avoid creating and
maintaining a separate network forwarding authentication/
authorization scheme decoupled from the end-to-end authentication/
authorization system of the application.
If delivery of such high value content in conjunction with the
peering described here is desired, the short term recommendations are
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for sources to clearly isolate the source and group addresses used
for different content bundles, communicate those (S,G) patterns from
AD-1 to the AD-2 and let AD-2 leverage existing per-EU
authentication/ authorization mechanisms in network devices to
establish filters for (S,G) sets to each EU.
6.3. Peering Encryption
Encryption at peering points for multicast delivery may be used per
agreement between AD-1/AD-2.
In the case of a private peering link, IP multicast does not have
attack vectors on a peering link different from those of IP unicast,
but the content owner may have defined high bars against
unauthenticated copying of even the end-to-end encrypted content, and
in this case AD-1/AD-2 can agree on additional transport encryption
across that peering link. In the case of a broadcast peering
connection (e.g.: IXP), transport encryption is also the easiest way
to prohibit unauthenticated copies by other ADs on the same peering
point.
If peering is across a tunnel going across intermittent transit ADs
(not discused in detail in this document), then encryption of that
tunnel traffic is recommended. It not only prohibits possible
"leakage" of content, but also to protects the the information what
content is being consumed in AD-2 (aggregated privacy protection).
See the following subsection for reasons why the peering point may
also need to be encrypted for operational reasons.
6.4. Operational Aspects
Section 4.3.3 discusses exchange of log information, this section
discussed exchange of (S,G) information and Section 7 discusses
exhange of program information. All these operational pieces of data
should by default be exchanged via authenticated and encrypted peer-
to-peer communication protocols between AD-1 and AD-2 so that only
the intended recipient in the peers AD have access to it. Even
exposure of the least sensitive information to third parties opens up
attack vectors. Putting for example valid (S,G) information into DNS
(as opposed to passing it via secured channels from AD-1 to AD-2) to
allow easier filtering of invalid (S,G) would also allow attackers to
easier identify valid (S,G) and change their attack vector.
From the perspective of the ADs, security is most critical for the
log information as it provides operational insight into the
originating AD, but it also contains sensitive user data:
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Sensitive user data exported from AD-2 to AD-1 as part of logs could
be as much as the equivalent of 5-tuple unicast traffic flow
accounting (but not more, e.g.: no application level information).
As mentioned in Section 7, in unicast, AD-1 could capture these
traffic statistics itself because this is all about AD-1 originated
traffic flows to EU receivers in AD-2, and operationally passing it
from AD-2 to AD-1 may be necessary when IP multicast is used because
of the replication happening in AD-2.
Nevertheless, passing such traffic statistics inside AD-1 from a
capturing router to a backend system is likely less subject to third
party attacks then passing it interdomain from AD-2 to AD-1, so more
diligence needs to be applied to secure it.
If any protocols used for the operational information exchange are
not easily secured at transport layer or higher (because of the use
of legacy products or protocols in the network), then AD-1 and AD-2
can also consider to ensure that all operational data exchange goes
across the same peering point as the traffic and use network layer
encryption of the peering point as discussed in before to protect it.
End-to-end authentication and authorization of EU may involve some
kind of token authentication and is done at the application layer
independently of the two AD's. If there are problems related to
failure of token authentication when end-users are supported by AD-2,
then some means of validating proper working of the token
authentication process (e.g., back-end servers querying the multicast
application source provider's token authentication server are
communicating properly) should be considered. Implementation details
are beyond the scope of this document.
Security Breach Mitigation Plan - In the event of a security breach,
the two AD's are expected to have a mitigation plan for shutting down
the peering point and directing multicast traffic over alternative
peering points. It is also expected that appropriate information
will be shared for the purpose of securing the identified breach.
7. Privacy Considerations
The described flow of information about content and the end-user
described in this document aims to maintain privacy:
AD-1 is operating on behalf (or owns) the content source and is
therefore part of the content-consumption relationship with the end-
user. The privacy considerations between the EU and AD-1 are
therefore in general (exception see below) the same as if no IP
multicast was used, especially because for any privacy conscious
content, end-to-end encryption can and should be used.
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Interdomain multicast transport service related information is
provided by the AD-2 operators to AD-1. AD-2 is not required to gain
additional insight into the user behavior through this process that
it would not already have without the service collaboration with AD-1
- unless AD-1 and AD-2 agree on it and get approval from the EU.
For example, if it is deemed beneficial for EU to directly get
support from AD-2 then it would in general be necessary for AD-2 to
be aware of the mapping between content and network (S,G) state so
that AD-2 knows which (S,G) to troubleshoot when the EU complains
about problems with a specific content. The degree to which this
dissemination is done by AD-1 explicitly to meet privacy expectations
of EUs is typically easy to assess by AD-1. Two simple examples:
For a sports content bundle, every EU will happily click on the "i
approve that the content program information is shared with your
service provider" button, to ensure best service reliability because
service conscious AD-2 would likely also try to ensure that high
value content, such as the (S,G) for SuperBowl like content would be
the first to receive care in case of network issues.
If the content in question was one where the EU expected more
privacy, the EU should prefer a content bundle that included this
content in a large variety of other content, have all content end-to-
end encrypted and the programming information not be shared with AD-2
to maximize privacy. Nevertheless, the privacy of the EU against
AD-2 observing traffic would still be lower than in the equivalent
setup using unicast, because in unicast, AD-2 could not correlate
which EUs are watching the same content and use that to deduce the
content. Note that even the setup in Section 3.4 where AD-2 is not
involved in IP multicast at all does not provide privacy against this
level of analysis by AD-2 because there is no transport layer
encryption in AMT and therefore AD-2 can correlate by onpath traffic
analysis who is consuming the same content from an AMT relay from
both the (S,G) join messages in AMT and the identical content
segments (that where replicated at the AMT relay).
In summary: Because only content to be consumed by multiple EUs is
carried via IP multicast here, and all that content can be end-to-end
encrypted, the only IP multicast specific privacy consideration is
for AD-2 to know or reconstruct what content an EU is consuming. For
content for which this is undesirable, some form of protections as
explained above are possible, but ideally, the model of Section 3.4
could be used in conjunction with future work adding e.g.: dTLS
[RFC6347] encryption between AMT relay and EU.
Note that IP multicast by nature would permit the EU privacy against
the countent source operator because unlike unicast, the content
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source does not natively know which EU is consuming which content: In
all cases where AD-2 provides replication, only AD-2 does know this
directly. This document does not attempt to describe a model that
does maintain such level of privacy against the content source but
only against exposure to intermediate parties, in this case AD-2.
8. IANA Considerations
No considerations identified in this document.
9. Acknowledgments
The authors would like to thank the following individuals for their
suggestions, comments, and corrections:
Mikael Abrahamsson
Hitoshi Asaeda
Dale Carder
Tim Chown
Leonard Giuliano
Jake Holland
Joel Jaeggli
Albert Manfredi
Stig Venaas
Henrik Levkowetz
10. Change log [RFC Editor: Please remove]
Please see discussion on mailing list for changes before -11.
-11: version in IESG review.
-12: XML'ified version of -11, committed solely to make rfcdiff
easier. XML versions hosted on https://www.github.com/toerless/
peering-bcp
-13:
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o IESG feedback. Complete details in:
https://raw.githubusercontent.com/toerless/peering-bcp/master/11-
iesg-review-reply.txt
o Ben Campbell: Location information about EU (End User) is Network
Locatio information
o Ben Campbell: Added explanation of assumption to introduction that
traffic is sourced from AD-1 to (one or many) AD-2, mentioned that
sourcing from EU is out of scope.
o Introduction: moved up bullet points about exchanges and transit
to clean up flow of assumptions.
o Ben Campbell: Added picture for the GRE case, visualized tunnels
in all pictures.
o Ben Campbell: See 13-discus.txt on github for more details of
changes for this review.
o Alissia Cooper: Added more explanation for Log Management,
explained privacy context.
o Alissia Cooper: removed pre pre-RFC5378 disclaimer.
o Alissia Cooper: removed mentioning of potential mutual
compensation between domains if the other violates SLA.
o Mirja Kuehlewind: created section 4.1.1 to discuss congestion
control more detailled, adding reference to BCP145, removed stub
CC paragraphs from section 3.1 (principle applies to every section
3.x, and did not want to duplicate text between 3.x and 4.x).
o Mirja Kuehlewind: removed section 8 (conclusion). Text was not
very good, not important to hae conclusion, maybe bring back with
better text if strong interest.
o Introduced section about broadcast peering points because there
where too many places already where references to that case
existed (4.2.4).
o Introduced section about privact considerations because of comment
by Ben Campbell and Alissa Cooper.
o Rewrote security considerations and structured it into key
aspects: DoS attacks, content protection, peering point encryption
and operational aspects.
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o Kathleen Moriarty: Added operational aspects to security section
(also for Alissia), e.g.: covering securing the exchange of
operational data between ADs.
o Spencer Dawkins: Various editorial fixes. Removed BCP38 text from
section 3, superceeded be explanation of PIM-SM RPF check to
provide equvialent security to BCP38 in security section 7.1).
o Eric Roscorla: (fixed from other reviews already).
o Adam Roach: Fixed up text about MDH-04, added reference to
RFC4786.
-13: Fix for Mirja's review on must for congestion control.
11. References
11.1. Normative References
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
DOI 10.17487/RFC2784, March 2000,
<https://www.rfc-editor.org/info/rfc2784>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Protocol Version 2 (MLDv2) for Source-
Specific Multicast", RFC 4604, DOI 10.17487/RFC4604,
August 2006, <https://www.rfc-editor.org/info/rfc4604>.
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[RFC4609] Savola, P., Lehtonen, R., and D. Meyer, "Protocol
Independent Multicast - Sparse Mode (PIM-SM) Multicast
Routing Security Issues and Enhancements", RFC 4609,
DOI 10.17487/RFC4609, October 2006,
<https://www.rfc-editor.org/info/rfc4609>.
[RFC7450] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450,
DOI 10.17487/RFC7450, February 2015,
<https://www.rfc-editor.org/info/rfc7450>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[BCP38] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>.
[BCP41] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>.
[BCP145] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
11.2. Informative References
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
December 2006, <https://www.rfc-editor.org/info/rfc4786>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[INF_ATIS_10]
"CDN Interconnection Use Cases and Requirements in a
Multi-Party Federation Environment", ATIS Standard
A-0200010, December 2012.
[MDH-04] Thaler, D. and others, "Multicast Debugging Handbook",
IETF I-D draft-ietf-mboned-mdh-04.txt, May 2000.
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Internet-DraftMulticast Across Inter-Domain Peering Points October 2017
[Traceroute]
, <http://traceroute.org/#source%20code>.
[I-D.ietf-mboned-mtrace-v2]
Asaeda, H., Meyer, K., and W. Lee, "Mtrace Version 2:
Traceroute Facility for IP Multicast", draft-ietf-mboned-
mtrace-v2-20 (work in progress), October 2017.
Authors' Addresses
Percy S. Tarapore (editor)
AT&T
Phone: 1-732-420-4172
Email: tarapore@att.com
Robert Sayko
AT&T
Phone: 1-732-420-3292
Email: rs1983@att.com
Greg Shepherd
Cisco
Email: shep@cisco.com
Toerless Eckert (editor)
Futurewei Technologies Inc.
Email: tte+ietf@cs.fau.de
Ram Krishnan
SupportVectors
Email: ramkri123@gmail.com
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