Use of Multicast Across Inter-Domain Peering Points

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: 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. 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: 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. 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. 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. 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 for more details about that option. Administrative Domain 1 (AD-1) is enabled with native multicast. A peering point exists between AD-1 and AD-2. It is understood that several protocols are available for this purpose including PIM-SM and Protocol Independent Multicast - Source Specific Multicast (PIM-SSM) , Internet Group Management Protocol (IGMP) , and Multicast Listener Discovery (MLD) . As described in , 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 . 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. 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. An Automatic Multicast Tunnel (AMT) 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 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). 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. 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.

A multicast-based application delivery scenario is as follows: Two independent administrative domains are interconnected via a peering point. 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: A Generic Routing Encapsulation (GRE) Tunnel allowing multicast tunneling across the peering point, or An Automatic Multicast Tunnel (AMT) . 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 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. An End User (EU) controls a device connected to AD-2, which runs an application client compatible with the service provider's application source. 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. 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 . The peering point architecture and requirements may have some unique aspects associated with the Enterprise case. These unique aspects will also be described in . 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.

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.

This Use Case involves end-to-end Native Multicast between the two administrative domains and the peering point is also native multicast enabled - see .

| 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 ]]> Advantages of this configuration are: Most efficient use of bandwidth in both domains. 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: Dual homing for peering points between domains is recommended as a way to ensure reliability with full BGP table visibility. 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 ). 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. 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.

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 .

|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 ]]> In this case, the interconnection I1 between AD-1 and AD-2 in is multicast enabled via a Generic Routing Encapsulation Tunnel (GRE) 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 . 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: Highly efficient use of bandwidth in both domains, although not as efficient as the fully native multicast Use Case. Fewer devices in the path traversed by the multicast stream when compared to an AMT enabled peering point. 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 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). GRE is an existing technology and is relatively simple to implement. Disadvantages of this configuration: Per Use Case 3.1, current router technology cannot count the number of end users or the number bytes transmitted. GRE tunnel requires manual configuration. The GRE must be established prior to stream starting. 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: GRE tunnels are typically configured manually between peering points to support multicast delivery between domains. 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).

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.

|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 ]]> Advantages of this configuration: Highly efficient use of bandwidth in AD-1. AMT is an existing technology and is relatively simple to implement. Attractive properties of AMT include the following: Dynamic interconnection between Gateway-Relay pair across the peering point. Ability to serve clients and servers with differing policies. Disadvantages of this configuration: 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. Additional devices (AMT Gateway and Relay pairs) may be introduced into the path if these services are not incorporated in the existing routing nodes. 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, 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.

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.

|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. ]]> 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. Advantages of this configuration: Efficient use of bandwidth in AD-1 (The closer AR is to uBR, the more efficient). 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. 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. AMT is an existing technology and is relatively simple to implement. Attractive properties of AMT include the following: Dynamic interconnection between Gateway-Relay pair across the peering point. Ability to serve clients and servers with differing policies. 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: Additional devices (AMT Gateway and Relay pairs) are introduced into the transport path. 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. 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. 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.

This is a variation of Use Case 3.4 as follows:

|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 ]]> 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: 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. One such node is at the AD-2 side of the peering point (node AGAR1 in above Figure). 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. 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. 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. 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. 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. 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.

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.

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. Number of Peering Points. Peering Point Addresses and Locations. Connection Type - Dedicated for Multicast delivery or shared with other services. Connection Mode - Direct connectivity between the two AD's or via another ISP. 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 and MBGP . 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. QoS Requirements - Delay and/or latency specifications that need to be specified in an SLA. AD Roles and Responsibilities - the role played by each AD for provisioning and maintaining the set of peering points to support multicast delivery.

Like IP unicast traffic, IP multicast traffic carried across non-controlled networks must comply to Congestion Control Principles as described in and explained in detail for UDP IP multicast in . 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 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.

The main objective for multicast delivery routing is to ensure that the End User receives the multicast stream from the "most optimal" source which typically: Maximizes the multicast portion of the transport and minimizes any unicast portion of the delivery, and 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: To be scalable, To avoid or minimize new protocol development or modifications, and To be robust enough to achieve high reliability and automatically adjust to changes and problems in the multicast infrastructure. 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.

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: 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. The client uses the join message with S,G to join the multicast stream . To facilitate this process, the two AD's need to do the following: Advertise the source id(s) over the Peering Points. Exchange relevant Peering Point information such as Capacity and Utilization. Implement compatible multicast protocols to ensure proper multicast delivery across the peering points.

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. The two AD's need to follow the same process as described in 4.2.1 to facilitate multicast delivery across the Peering Points.

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: Find the closest AMT relay to the end-user that also has multicast connectivity to the content source, and Minimize the AMT unicast tunnel distance. There are essentially two components to the AMT specification 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. 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 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 . 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: 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. 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. 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. 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 . 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. The AMT Gateway uses that unicast IP address to initiate a three- way handshake with the AMT Relay. AMT Gateway provides "S,G" to the AMT Relay (embedded in AMT protocol messages). 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. AMT Relay encapsulates the multicast stream into the tunnel between the Relay and the Gateway, providing the requested content to the EU.

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 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: 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. 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. 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).

Back Office refers to the following: Servers and Content Management systems that support the delivery of applications via multicast and interactions between AD's. Functionality associated with logging, reporting, ordering, provisioning, maintenance, service assurance, settlement, etc.

Resources for basic connectivity between AD's Providers need to be provisioned as follows: Sufficient capacity must be provisioned to support multicast-based delivery across AD's. 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. 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: 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). 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). 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. 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: 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. 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.

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: A unique identifier is recommended to designate each master account. 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 ): 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.

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 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: Usage information logs at aggregate level. Usage failure instances at an aggregate level. 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. Security logs, aggregated or summarized according to agreement (with additional detail potentially provided during security events, by agreement). Access logs (EU), when needed for troubleshooting. Application logs (what is the application doing), when needed for shared troubleshooting. 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: 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. Aggregated or summarized logs according to agreement (with additional detail potentially provided during security events, by agreement).

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: 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. 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; 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. 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. 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. 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:Kind of problem(s). Starting point & duration of problem(s). Conditions in which problem(s) occur. IP address blocks of affected users. ISPs of affected users. Type of access e.g., mobile versus desktop. Network locations of affected EUs. Both AD's conduct some form of root cause analysis for multicast service delivery problems. Examples of various factors for consideration include:Verification that the service configuration matches the product features. Correlation and consolidation of the various customer problems and resource troubles into a single root service problem. Prioritization of currently open service problems, giving consideration to problem impact, service level agreement, etc. Conduction of service tests, including one time tests or a series of tests over a period of time. Analysis of test results. Analysis of relevant network fault or performance data. Analysis of the problem information provided by the customer (CP). 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.

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.

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.

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. It is recommended that multicast diagnostics will be performed leveraging established operational practices such as those documented in . 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 and . 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. 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. 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.

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 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 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 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.

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. 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 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.

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.

discusses exchange of log information, this section discussed exchange of (S,G) information and 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: 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 , 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.

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. 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 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 could be used in conjunction with future work adding e.g.: dTLS 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 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.

No considerations identified in this document.

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

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: IESG feedback. Complete details in: https://raw.githubusercontent.com/toerless/peering-bcp/master/11-iesg-review-reply.txt Ben Campbell: Location information about EU (End User) is Network Locatio information 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. Introduction: moved up bullet points about exchanges and transit to clean up flow of assumptions. Ben Campbell: Added picture for the GRE case, visualized tunnels in all pictures. Ben Campbell: See 13-discus.txt on github for more details of changes for this review. Alissia Cooper: Added more explanation for Log Management, explained privacy context. Alissia Cooper: removed pre pre-RFC5378 disclaimer. Alissia Cooper: removed mentioning of potential mutual compensation between domains if the other violates SLA. 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). 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. Introduced section about broadcast peering points because there where too many places already where references to that case existed (4.2.4). Introduced section about privact considerations because of comment by Ben Campbell and Alissa Cooper. Rewrote security considerations and structured it into key aspects: DoS attacks, content protection, peering point encryption and operational aspects. Kathleen Moriarty: Added operational aspects to security section (also for Alissia), e.g.: covering securing the exchange of operational data between ADs. 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). Eric Roscorla: (fixed from other reviews already). Adam Roach: Fixed up text about MDH-04, added reference to RFC4786. -13: Fix for Mirja's review on must for congestion control.