INTERNET-DRAFT D. Qi, ed.
Intended status: Informational Bloomberg
Expires: January 03, 2018
N. Bitar, ed.
Nokia
T. Boyes
Bloomberg
S. Palislamovic
Nokia
A. Lohiya
Juniper
Expires: January 2018 July 03, 2017
Software-Defined Multicast Network Overlay Framework
draft-qi-bitar-intarea-sdn-multicast-overlay-01
Abstract
This document describes a framework for IP multicast based on
the software defined networking paradigm. The framework enables
flexible allocation of multicast responsibilities to designated
control and forwarding elements, and provides for multicast
path computation and programming of the forwarding plane. The
objective of this framework is to enable network operators to
support IP multicast in an IP/MPLS core free of Protocol-
Independent-Multicast (PIM) and MPLS multicast control. The
forwarding paradigm provides for multicast replication over
unicast and multicast overlays at designated edges, and for
native IP and MPLS multicast replication and forwarding in the
core.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance
with the provisions of BCP 78 and BCP 79.
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Conventions used in this document
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"OPTIONAL" in this document are to be interpreted as described
in RFC-2119 [RFC2119].
Table of Contents
1. Introduction ................................................ 4
2. Terminology ................................................ 4
3. Acronyms ...............................................5
4. Problem Statement ........................................... 6
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5. Multicast SDN Framework Benefits ............................ 8
6. Multicast SDN Framework Guiding Principles and Requirements .10
7. Multicast SDN Framework Architectural Components ............12
8. SDN Multicast Framework .....................................15
8.1. SDN Multicast Operational Models .......................16
8.1.1. Full Multicast SDN Model Operational Overview ......16
8.1.2. Hybrid Distributed-SDN Multicast Model Operational
Overview ..................................................18
8.1.3. Cut-Through Operational Mode .......................18
8.1.4. Summary of Control an Data Planes Applicable to the
SDN Multicast Models and Gaps .............................19
8.2. SDN Multicast Overlay Control Plane Functionalities ... 21
8.2.1. Unicast Topology Discovery .........................21
8.2.2. Multicast Topology Discovery .......................22
8.2.3. Resource Utilization Monitoring ....................22
8.2.4. Multicast Group Membership Discovery ...............22
8.2.5. Multicast Sender Discovery .........................23
8.2.6. Multicast distribution tree creation and
maintenance ...............................................23
8.2.7. Multicast forwarding programmability ...............24
8.2.8. Entitlement admission control ......................25
8.2.9. Bandwidth Admission control ........................25
8.3. Multicast Functional Components Implementation .........25
8.4. SDN Multicast Management Interfaces ....................26
8.4.1. North-Bound Interface ..............................26
8.4.2. Multicast SDN Functional Component Facing
Interfaces ................................................26
8.4.3. Traditional Underlay Network Element Interfaces ....26
8.4.4. Information Model and Data Model of Management
Interfaces ................................................27
9. SDN Control Plane ...........................................27
10. Multi-Party Multicast SDN Overlay Interaction ..............27
11. Security Considerations ....................................27
12. IANA Considerations ........................................28
13. References .................................................28
13.1. Normative References ..................................28
13.2. Informative References ................................28
14.0 Acknowledgments ...........................................30
Authors Addresses ..............................................30
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1. Introduction
Operators that enable multicast services in their network have
traditionally relied on host-based multicast protocols such as
Internet Group Management Protocol (IGMP), and core-based
multicast protocols such as Protocol Independent Multicast
(PIM) with its variants, and more recently MPLS multicast
protocols. Some operators have encountered issues with these
protocols that have ensued from protocol activities, and perhaps
implementation behavior under some scale, that overloaded the
control plane of the routing nodes, sometimes effecting
scalability, and often leading to network instability. There
are four sources for this activity: (1) high dynamicity of
group membership, resulting in a high rate of join/leave, (2)
refresh of multicast soft state, (3) faulty implementation, and
(4) malicious attacks.
This document describes a framework for IP multicast based on
the software-defined networking (SDN) paradigm. The objective
of this framework is to allow an operator to flexibly design IP
multicast networks to fit its needs, and minimize network risks.
Specifically, it enables an operator to provide for multicast
services in its network without PIM or MPLS multicast signaling
protocols (i.e., point to multipoint Resource Reservation
protocol - Traffic Engineering (RSVP-TE), or Multicast Label
Distribution Protocol (MLDP)). The elimination of these
protocols from network elements alleviates a good amount of
control plane activity often consumed by these protocols to
establish and maintain multicast soft sate, minimizing network
stability risks and providing for better scale.
The SDN control plane described in this framework, provides for
(1) processing join and leave requests from receivers (e.g.,
IGMP, PIM) or applications that request the addition or pruning
of receivers, (2) multicast entitlement and bandwidth admission
control, (3) the computation of a multicast path if necessary,
and (4) the establishment of the necessary forwarding states in
the nodes on the computed forwarding path.
2. Terminology
This document adopts the following SDN terminology from RFC7426
(SDN: Layers and Architecture Terminology):
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- Software-Defined Networking (SDN): A programmable
network approach that supports the separation of control and
forwarding planes via standardized interfaces.
- Forwarding Plane (FP): The collection of resources across
all network devices responsible for forwarding traffic.
- Control Plane (CP): The collection of functions responsible
for controlling one or more network devices. CP instructs
network devices with respect to how to process and forward
packets. The control plane interacts primarily with the
forwarding plane and, to a lesser extent, with the operational
plane.
Furthermore, this document adopts the following terminology
from RFC 7365, Framework for Data Center (DC) Network
Virtualization:
Tenant: The customer using a virtual network and any associated
resources (e.g., compute, storage, and network). A tenant
could be an enterprise or a department/organization within an
enterprise.
Tenant System: A physical or virtual system that can play the
role of a host or a forwarding element such as a router,
switch, firewall, etc. It belongs to a single tenant and
connects to one or more virtual networks (VNs) of that tenant.
3. Acronyms
ASM: Any-Source Multicast
MSN: Multicast Service Node
MSE: Multicast Service Edge
MBG: Multicast Border Gateway
SSM: Source-Specific Multicast
TES: Tenant End System
VM: Virtual Machine
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VN: Virtual Network
VXLAN: Virtual eXtensible LAN
DC: Datacenter
4. Problem Statement
IP multicast in core IP networks has prevailingly relied on
PIM-ASM to establish a multicast tree between the first hop
router connected to a sender and the edge routers connected
to receivers, and relied on multicast source discovery protocols
to discover multicast sources. PIM is a soft state protocol
that relies on periodic join refreshes to keep the multicast
states alive and its mode of forwarding requires data-driven
events. While PIM-SSM removed some of the above issues for
PIM-ASM, it is IGMPv3 dependent and requires out-of-band
source discovery mechanism. MPLS multicast signaling protocols,
namely point to multipoint RSVP-TE, imposes similar control
load on MPLS routers. On access links, edge routers process
IGMP messages from attached receivers or CPEs, or PIM messages
from attached CPEs. These messages signal to edge routers the
multicast membership state of the attached devices. IGMP is
also soft state, requiring periodic refreshes of join/prune
messages to refresh multicast membership state, or queries to
clean up stale state.
Multicast group activity (joining/leaving a multicast group)
could be very dynamic, resulting in a high control message
rate that increases with the number of multicast receivers,
and is highly dependent on the behavior of these receivers in
leaving/joining multicast groups.
All this control plane activity is performed on (all) nodes
in the network to support multicast, risking network control
plane scale and stability.
Routers not only run multicast control protocols, but also
perform data plane multicast, holding multicast forwarding
state and performing packet replication and forwarding.
Multicast forwarding state is dependent on the number of
multicast groups ((*,G) or (S,G)) and number of outgoing
interfaces per multicast group. As receivers join or leave
multicast groups, these multicast forwarding entries need to
be updated, further adding to a router control plane load. A
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large number of (*,G)/(S, G) multicast states and control
information push against the resource limit of network
routing hardware (e.g., TCAM, CPU). On an edge node where the
number of outgoing interfaces could be very large, this
activity is further exacerbated. In addition, data
replication shares forwarding capacity (processing cycles and
bandwidth) with unicast, often mandating the need to control
the capacity allocated for multicast and enforcing it.
Native multicast protocol procedures do not address the
protection of a router control plane and data plane resources
from the negative impacts that multicast enablement may have
on these resources. Such negative impacts could be the result
of malicious activities, misconfigurations, or simply lack of
control on legitimate activities. For instance, a receiver
may maliciously join a large number of multicast groups and
create shared bandwidth bottlenecks if allowed to
successfully join these groups. Such a receiver may also
generate IGMP reports at a very high frequency, creating an
attack on the access router control plane if not properly
controlled. A host may also masquerade itself as a source for
many multicast groups, resulting in the creation of a large
number of forwarding state on the access router and other
core nodes. Some router vendors have implemented mechanisms
to protect against such attacks (malicious or not) on the
router control and data plane, but often these mechanisms are
not implemented, partially implemented or not implemented
with a consistent behavior let alone configuration as they
are vendor proprietary. Lack of consistency poses challenges
to network operators when multicast is to be enabled in a
multi-vendor environment.
Without some type of entitlement that could be defined and
uniformly enforced across all edge routers, a rogue multicast
sender that knows active multicast groups can send traffic to
these groups. The same goes for multicast receivers who may
snoop on multicast traffic that they are not entitled to by
simply joining the corresponding multicast group(s). Thus,
there is a need to define and enforce entitlement for
receivers to join multicast groups and for senders to be able
to send traffic to multicast groups to protect against the
negative impacts that sender and receiver misconfigurations
or malicious activities could inflict.
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There is need to (1) protect against multicast control
plane message attacks that may or may not result in a
receiver successfully joining a multicast group, (2) be able
to define and enforce entitlement for both receivers of and
senders to multicast groups, and (3) to protect against the
oversubscription of resources beyond set engineering targets
by performing resource (bandwidth and other resources)
admission control.
Multicast entitlement, admission control and control DDoS
protection are hard to implement in existing networks when
relying on router vendor implementations as they do not
holistically or uniformly address all needs, if any.
Finally, there is no multicast management plane or north-
bound interface to harness multicast control state and
telemetry information that enable monitoring the state of the
network and enable controlling the usage of network resources.
5. Multicast SDN Framework Benefits
The multicast SDN framework is composed of an overlay control
plane that computes multicast distribution paths between
senders and receivers per multicast group/channel, and
establishes the forwarding path on forwarding elements,
enabling the distribution of multicast traffic between these
senders and receivers, and provides for increased
functionality and flexibility. The multicast overlay control
plane on centralized multicast SDN controller(s) alleviates
the multicast control plane activities performed by routing
nodes in traditional networks. The controller could be an
existing controller with multicast capability or a separate
multicast controller.
The multicast SDN framework provides the following benefits:
- By alleviating multicast control protocols and associated
processing and states off the distributed traditional
routing nodes in a network, the routing control plane of
these nodes will have an order of magnitude reduction in
complexity and a significant reduction in processing load,
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improving network stability and scalability and faster time
to recovery from failures.
- Much fine grained policy and advanced service enhancements
such as multicast control policy (access control, admission
control, entitlements and bandwidth), can be implemented
directly and consistently in the SDN multicast control
plane. This functionality can be and has been implemented
in traditional routers but at the expense of additional
processing requirements on the control plane and the burden
of ensuring consistent implementation across various
vendors.
- Much fine grained multicast path selection based on various
attributes (e.g., bandwidth, diversity, latency) and
programming, and various degree of replication, alleviating
the current congruency between multicast and unicast
topologies and providing flexibility in carving multicast
paths for multicast groups and receivers.
- Multicasting across Campus, Datacenter, Wide Area Network,
and multiple administrative boundaries under the same
enterprise control can be implemented with a unified and
integrated Management Plane and Control Plane.
- Multicasting across administrative boundaries under the
control of different enterprises/operators,
can be implemented leveraging SDN mechanisms and/or
traditional distributed control mechanisms, depending on
the capabilities of the neighboring enterprise/operator
domains.
- Control and/or management plane applications can
compute, modify, steer, and program forwarding plane
multicast paths, and query and harness state information
from the routing nodes performing multicast forwarding
using north bound interfaces from these nodes.
- Flexible design of the multicast services in the operator
network to address operator design principles and
the capabilities of the forwarding elements.
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- Agnosticism to whether an endpoint, multicast receiver or
sender, is a VM, container, or a physical host as they
all use the same overlay multicast service mechanisms.
- Applications can steer multicast path, query and harness
state information from SDN multicast overlays using
northbound interfaces.
6. Multicast SDN Framework Guiding Principles and Requirements
Following are the requirements that MUST be satisfied by the
Multicast SDN framework:
- No constraint on the network topology. The SDN framework will
need to be aware of the unicast and multicast network
topology when it needs to compute unicast and multicast paths
that satisfy certain constrains and/or to optimize for
network usage resources on these paths.
- No constraint on the unicast routing protocol selection in the
underlay network. The network may consist of multiple domains
with different unicast routing protocols.
- Be agnostic to other services in the network (e.g.,
BGMP/MPLS unicast and multicast Layer2 and Layer3 services,
other types of VPN services). That is, it MUST allow new
multicast services to be enabled based on this framework in
the presence of other services.
- Support IPv4, IPv6, and MPLS unicast underlay data plane,
providing for edge replication over IPv4, IPv6,or MPLS
unicast overlays.
- Support IPv4, IPv6, and MPLS multicast data planes, providing
for replication over IPv4, IPv6, and MPLS
multicast overlays, and for the computation and programmability
of the overlay data paths on the underlay as needed.
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- Support a BIER [BIER-ARCH] underlay data plane to support
multicast replication of multicast packets over BIER type of
multicast overlays.
- Support a segment-routing (SR) [SR-ARCH] underlay data plane to
support edge replication of multicast packets over unicast SR
overlays with both IP and MPLS data planes.
- Support stitching of multicast packets across domains with
the different control and data planes stated in the earlier
requirements.
- Integrate with network multicast (control and data plane)
where operationally feasible resulting in optimum bandwidth
utilization in data plane.
- Enable decoupling of multicast topology from unicast
topology, providing the ability to enable multicast
selectively on nodes, and/or carving multicast paths.
- Enable select edge data replication nodes, specifically when
the first hop router connected to the Multicast sender is not
best suited for data replication.
- Support existing multicast applications without requiring any
modification to these applications, e.g., applications that
use IGMP for multicast membership
- Support the tunable aggregation of multicast groups on
multicast tunnels (where tunnels may be stateful tunnels,
or simply encapsulation headers)
- Enabling operators to traded-off multicast data plane
bandwidth efficiency with multicast data plane and control
plane state
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- Support multicast admission control on unicast tunnels/paths,
multicast tunnels, and path (re-) computation on the
underlay.
- Support multicast admission control based on entitlement of
the receiver to a multicast group or channel
- Support programmability of multicast traffic policers and
filter policies
7. Multicast SDN Framework Architectural Components
Multicast Service Edge (MSE):
An MSE connects to tenant end systems (TESs) (hosts) on the
access side and to an underlay IP network or IP/MPLS network on
the network side. In the forwarding plane, When an MSE receives
a user IP multicast packet from a TES on the access side, it
replicates the packet on local ports with TES receivers, and
encapsulates the IP multicast packet in a unicast packet to a
Multicast Service Node (MSN) or a Multicast Border Gateway
(MBG) to reach remote multicast receivers. It also receives IP
multicast packets encapsulated in unicast packets on the
network side, decapsulates the multicast packets and replicates
them on local ports to corresponding TES receivers. In the
control plane, an MSE connects to a multicast controller that
programs the MSE with multicast forwarding entries triggered by
management entities or dynamic control protocols. An MSE may
receive IGMP or Multicast Listener Discovery protocol (MLD)
report/leave packets on the access side. The MSE acts as an
IGMP/MLD proxy and sends messages to the multicast SDN
controller to inform the controller of local multicast receivers
for a multicast group or channel. It may also be statically
programmed with multicast entries. An MSE supporting multi-tenancy
provides for multicast control and forwarding in a tenant specific
virtual routing and forwarding context. It can be implemented in
hardware or software. For example, it can be part of a virtual
router in a virtualized environment, a kernel or user-plane
routing function in physical servers, a physical router, or
appliance which performs multicast service functions.
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There are multiple ways an MSE can intercept multicast control
messages and multicast data packets from TESs when the TESs
are receivers and senders, respectively:
- MSE is a multicast router on local VLAN
- MSE is a designated multicast router for a LAN router. A LAN
router (e.g., a Top of rack (ToR) router in a DC) forwards
all multicast packets it receives to a designated MSE
- MSE is part of virtual switch/router on a virtualized host
- MSE is a kernel function and intercepts data frames
- MSE resides in a NIC of the TES and intercepts all frames in
and out of the NIC.
- MSE is a customer edge (CE) router for a local site.
Multicast Tunnel TES (MT-TES):
An MT-TES is a tenant end system (host), virtual or physical,
that may send or receive multicast packets encapsulated in
unicast IP/UDP packets and delivers them to local applications
based on the UDP port number in the encapsulating header or
multicast destination address.
Multicast Service Node (MSN):
An MSN is the network entity that receives and replicates
IP/Multicast packets from/to others MSNs, MBGs, MSEs and MT-
TESs in the data plane. An MSN is often designated to serve an
MSE with multicast receivers and senders, and/or MT-TESs. There
could be more than one MSN serving the same MSE or the same MT-
TES. In that case, the selection of the MSN can be based on
whether the MSE or MT-TES is sending or receiving multicast
packets to/from the network, and/or multicast group address or
multicast channel based on the tuple multicast source (S) and
multicast group address (G). An MSN may tunnel packets over the
underlay network to other MSNs and MBGs using unicast
tunnels/unicast header encapsulation, or may forward multicast
packets natively on the underlay. An MSN always forwards
multicast traffic encapsulated in unicast packets to MSEs and
MT-TESs as programmed. On the network side, an MSN may
participate in native IP multicast control and forwarding if so
configured. The multicast controller MAY also program underlay
multicast forwarding entries and the forwarding unicast entries
that correspond to the unicast forwarding information in the
encapsulating header of the packet carrying multicast packets
on the MSN for policy-based routing and forwarding purposes.
Alternatively, the unicast packets, encapsulating the multicast
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packets, can be forwarded based on underlay dynamic unicast
routing, the default behavior. Unlike MSE, MSN does not connect
to access networks or TESs. MSN can optimize replication based on
latency, bandwidth, QoS, number of multicast states desired or
even more specific multicast application requirements.
MSN can be implemented in hardware or software. For example, it
can be a physical router, or a software appliance which performs
multicast service functions. Each MSN has a forwarding plane and
a control plane, albeit new control plane functionality and
traditional control plane functionality implemented today are
relegated to an SDN multicast controller.
Multicast SDN Domain (MSD):
A multicast SDN domain encompasses forwarding nodes (MSEs,
MSNs, and MBGs) and a cluster of one or more multicast SDN
controllers that control the programming of tenant multicast
forwarding entries on these nodes in addition to underlay core
nodes that provide for IP connectivity among these nodes.
Multicast Border Gateway (MBG):
An MBG is a network forwarding node that sits at the border of
a multicast SDN domain and connects to other networks in
different domains, which could be either multicast SDN domains
or traditional networks with multicast capabilities in the same
or different administrative domains. An MBG forwards multicast
packets from one domain to another across the boundary and
forwards packets to MSNs within its domain. An MBG could also
implement MSN functionality, serving MSEs and MT-TESs. As an
example, in cloud networking whereby the cloud is composed of
multiple data centers (DCs), an MBG may perform the function of
a DC multicast gateway to the WAN to provide for the forwarding
of multicast traffic originated by one TES in one DC to TESs
located in other DCs. In this case, the MBG may use BGP/MPLS
Multicast VPN (BGP-MVPN) [RFC 6513] across the WAN. Inside a
domain, an MBG may be enabled with traditional IP multicast
control and forwarding on the network underlay links to perform
underlay multicast forwarding. Alternatively, underlay
multicast forwarding entries reachable within the domain may be
programmed by the corresponding multicast SDN control plane.
Overlay traffic may be tunneled to/from the MBG using unicast
tunnels/unicast-header encapsulation or multicast
tunnels/multicast header encapsulation.
An MBG can be implemented in hardware or software. For example,
it can be a physical router, or a software appliance which
performs multicast service functions albeit new control plane
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functionality and traditional control plane functional
implemented today are relegated to an SDN multicast controller.
Core Node (CN):
A CN is a routing node which provides the underlay
interconnectivity among the MSEs, MSNs and MBGs. It provides for
unicast IP, MPLS, and SR forwarding and may provide multicast IP,
MPLS and/or BIER forwarding.
8. SDN Multicast Framework
Figure 1 depicts the SDN multicast framework, specifically the
SDN management plane, control plane and data plane functional
elements and their interactions. In the full SDN model, control
of any data plane element for multicast is under the control of
the Multicast SDN control plane. Variants of this model that
leverage existing solutions (e.g., BGP-MVPN) are described in
this document to fit different deployment models.
+------------------------------------+
| |
| Management/Application |
| |
+------------------------------------+
^
|MApp-C
|
+-----------------------------------------------+
| |
| Multicast SDN Control |
| |
+-----------------------------------------------+
^ ^ ^ ^ ^ ^
|MSE-C |MSN-C |MBG-C |MC-C |MSN-C |MTTES-C
| | | | | |
| | | | | |
+----+ +---+ +---+ | +---+ +---+ ( ) +-------+
| TES|---|MSE|----|MSN|----|----| CN|----|MSN|-( )--| MT-TES|
+----+ +---+ +---+ | +---+ +---+ ( ) +-------+
IGMP |
MLD |
+---+
+--|MBG|--+
| +---+ |
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| |
| |
| Network |
| |
. | |
. \+-------+/
| MBG |
+-------+
Figure 1: SDN multicast framework reference diagram.
8.1. SDN Multicast Operational Models
8.1.1. Full Multicast SDN Model Operational Overview
This section provides an overview of the full SDN multicast
model and describes the transactions and information that needs
to be exchanged across the different interfaces, including the
interfaces between the multicast SDN controller and the various
multicast nodes (MSE, MSN, CN, MBG). Throughout this section
it should be assumed that all multicast operations on any of
the edge nodes are done in a tenant context. In the case of
multi-tenancy, MSEs, MSNs and MBGs must be able to perform
destination lookup and forwarding in a virtual routing and
forwarding (VRF) context. In addition, they must be able to
encapsulate the original multicast packet with a unicast
(tunnel) header and additional header information that carries
a tenant identifier that can be used to identify the forwarding
context at the receiving end.
Senders and receivers for a multicast group may be static or
dynamic. For each tenant and multicast group, the SDN multicast
controller is informed of the sender(s) via the controller
northbound management interface (MApp-C) or the MSE connected
to the sender(s) via the MSE-C interface. The SDN controller,
in the generic case, will select an MSN that will proxy the MSE
connected to the sender, and programs the MSE to send the
multicast group traffic it receives from the sender(s) to the
selected MSN. The SDN controller may select more than one such
MSN. The multicast group packets will be delivered to tenant
end systems served by other MSEs and MSNs from these selected
MSNs. For static TES multicast receivers on a particular group
or channel, the SDN controller knows which TESs are members of
a multicast group/channel via the MApp-C management interface,
and learns the MSE serving the TES via the MApp-C management
interface or via dynamic routing. Then for each TES on that
multicast group, The SDN controller selects the MSN to serve
the corresponding MSE. This selection could be based on certain
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criteria that optimize for bandwidth utilization on the path
between the MSN and the MSE, and/or resource utilization on the
MSN among others. Once an MSN selection is done to serve the
MSE, the SDN multicast controller needs to ensure that the
selected MSN receives the multicast group/channel traffic. The
SDN controller then selects the remote MSN from which it wants
to receive the multicast group packets. This latter selection
could be based on bandwidth utilization on the path between the
two MSNs in question, remote MSN resources, and/or the
transport method (multicast or unicast tunnel/tunneling
encapsulation). In the case of unicast transport, the remote
MSN proxying the sender MSE is programmed via the MSN-C interface
with a forwarding entry that results in encapsulating the
multicast group packets with a unicast SR, IP or MPLS tunnel or
encapsulation header that delivers the packets to the MSN serving
the receiver MSE. The MSN serving the receiver MSE is also
programmed with an entry that results in forwarding the received
multicast packet over another tunnel encapsulation to the
destination MSE. Optionally, the MSN serving the receiver MSE may
be programmed with the tunnel/encapsulation header information
over which the multicast group packets will be delivered (i.e.,
the sender MSN IP address or MPLS tunnel). Unicast forwarding is
based on dynamic routing information, static (policy-based)
routing or MPLS signaling in the case of RSVP-TE. In the case of
multicast transport, the SDN controller may choose to add a new
multicast tree branch to an existing multicast tree or re-compute
a new one rooted at the sender. In the case of IP multicast
transport, and in the absence of PIM in the core, the SDN
controller programs the CNs on the path with the appropriate
multicast forwarding entries. The MSE could also optionally be
programmed with the tunnel/header encapsulation information over
which packets are to be received.
For dynamic receivers, a TES may initiate an IGMP report or MLD
join message for a multicast group. That message should be
received by the MSE. The MSE may act as an IGMP proxy/MLD proxy
in which case the MSE, upon receiving the first join message
from a connected TES for a multicast group/channel, sends a
join message for that multicast group/channel with tenant
context to the SDN controller over the MSE-C interface. In
case there is requirement for entitlement or bandwidth
admission control, the MSE always sends a message to the SDN
controller over the MSE-C interface, requesting admission
control for the requesting TES for the particular
group/channel, including the tenant context. If the request is
admitted, the MSE is informed of the admission decision and the
transport path setup proceeds as described for the static
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receiver case. In the proxy case, when the last receiver leaves
a multicast group on the MSE either via an explicit leave,
failure to respond to a query or failing, the MSE sends a message
to the SDN controller that it no longer has receivers for that
group/channel via the MSE-C interface, and the controller may
remove the MSN as being a receiver for that group/channel and
take appropriate action removing associated forwarding state on
other nodes (MSNs, CNs).
8.1.2. Hybrid Distributed-SDN Multicast Model Operational
Overview
In this model, MSNs and MBGs perform the role of an BGP-MVPN PE
with a distributed BGP-MPLS control plane for exchanging
receiver information in a tenant network (MVPN) with other MSNs
and MBGs. The programmability of the MSNs with the receiver
information is done via the SDN controller to create the
relevant BGP policies and enable tunneling of multicast traffic
to served MSEs.
8.1.3. Cut-Through Operational Mode
In the cut-through model, a sender MSE can send multicast
packets directly to remote receiver MSE(s), bypassing MSNs and
MBGs. That is, MSNs do not proxy for downstream MSEs. In this
case, the multicast SDN controller programs a sender MSE via
the MSE-C interface with a forwarding entry that results in
encapsulating the multicast group packets received at the MSE
from the access network with a unicast IP header and a tenant
identifier that delivers these packets to remote receiver
MSE(s). The receiver MSE is also programmed with an entry that
results in forwarding the received multicast packet to
downstream multicast receivers. Similarly, Sender MSE can send
multicast packets directly to receiver MT-TESs with the same
operational procedures.
It should be noted that upon operator configuration, a
multicast deployment MAY include one or more of the operational
models described in the SDN multicast framework section.
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8.1.4. Summary of Control an Data Planes Applicable to the SDN
Multicast Models and Gaps
Table 1: Underlay and overlay control planes applicable
to the various SDN multicast models, and gaps (new).
----------------------------------------------------------------
|Model | Multicast Underlay | Multicast Overlay |
| | Control Plane | |
----------------------------------------------------------------
| Full SDN | MSE LAN access options: | MSE: MSE-MSDNC (new) |
| | IGMP, MLD, PIM, static | MSN: MSN-MSDNC (new) |
| | MSE/MSN/MBG/CN-MSDNC (new) | |
----------------------------------------------------------------
| Hybrid | MSE LAN access options: | MSE: MSE-MSDNC (new) |
| | IGMP, MLD, PIM, static | MSN: MSN-MSDNC (new) |
| | | |
| |MSN-MSE: None | MSN & MBG options: |
| |Core (MSN-CN-MBG) options: | MBGP (membership) |
| | MSDN Control | LISP[LISP][LISP-mcst]|
| | IGP (for BIER data plane)| |
| | PIM (core multicast IP) | |
| | MPLS multicast(MPLS core)| |
| | IGP (SR) | |
| | | |
| | MSDNC-MSDNC (new) | |
----------------------------------------------------------------
|Cut-Though|MSE LAN access options: | MSE options: |
| | IGMP, MLD, PIM | MSE-MSDNC (new) |
| | | MBGP (membership) |
| |MSE options: | LISP |
| | None | |
| | | |
| |Core (MSN-CN-MBG) options: | |
| | IGP (BIER data plane) | |
| | PIM (core multicast IP) | |
| | MPLS multicast(MPLS core)| |
| | | |
| | Multicast SDN Controller | |
| | (MSDNC)-MSDNC (new) | |
----------------------------------------------------------------
----------------------------------------------------------------
| Underlay Control Plane Protocol Options |
|Unicast: BGP OSP/ISIS (SR support) RSVP-TE/LDP |
|Multicast PIM IGMP/MLD pt-mpt RSVP-TE/mLDP |
----------------------------------------------------------------
| Overlay Control Plane Protocol Options |
| MBP LISP NVo3 (TBD) Multicast SDN (TBD) |
----------------------------------------------------------------
Figure 2: Summary of underlay and overlay control protocol
options.
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Table 2: Underlay and overlay data plane applicable
to the various SDN multicast models.
-----------------------------------------------------------------
|Model | Multicast Underlay | Multicast Overlay |
| | Data Plane | Data Plane |
-----------------------------------------------------------------
| Full SDN | MSE LAN access: | MSE LAN access: |
| and | IP multicast | Not applicable |
| Hybrid | | |
| | MSN,MBG and CN options:|MSE-MSN core options: |
| | -IP multicast | -IP multicast in IP VXLAN |
| | -BIER | or IP/GRE/VPN unicast |
| | -IP unicast | -IP multicast in SR VPN |
| | -SR | MPLS encap |
| | -MPLS unicast | -IP multicast in LISP |
| | -MPLS multicast | encap |
| | | |
| | | MSN/MBG options:: |
| | | -IP multicast in IP VXlAN |
| | | or IP/GRE/VPN o LISP |
| | | unicast |
| | | -IP multicast in BIER |
| | | -IP multicast in MPLS |
| | | VPN multicast |
| | | -IP multicast in SR VPN |
| | | MPLS |
----------------------------------------------------------------
|Cut-Through| MSE LAN access: | MSE LAN access: |
| | IP multicast | Not applicable |
| | | |
| | MSN,MBG and CN options:|Core(MSE-MSN) options: |
| | -IP multicast | -IP multicast in IP VXLAN |
| | -BIER | or IP/GRE/VPN unicast |
| | -IP unicast | -IP multicast in SR VPN |
| | -SR | MPLS encap |
| | -MPLS unicast | -IP multicast in LISP |
| | -MPLS multicast | uncap |
| | | |
----------------------------------------------------------------
----------------------------------------------------------------
| Underlay Data Plane Protocol Options |
| IPv4 IPv6 MPLS BIER SR|
|unicast/multicast unicast/multicast unicast/multicast |
----------------------------------------------------------------
| Shim header (carries tenant identifier: |
| VXLAN LISP GRE/MPLS MPLS |
-----------------------------------------------------------------
| Overlay Data Plane Protocols |
| IPv4 multicast IPv6 multicast |
----------------------------------------------------------------
Figure 3: Summary of underlay and overlay data plane protocol
options.
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8.2. SDN Multicast Overlay Control Plane Functionalities
Multicast control is traditionally distributed on network
routing elements, and mainly responsible for building and
maintaining multicast distribution trees or transport, and
configuring the multicast forwarding plane. Control Plane
entities may exchange multicast sender or receiver-membership
information with each other using network protocols such as MP-
BGP or PIM. The full multicast SDN model described in this
document alleviates the distributed control plane functions
from network elements but preserves the functionalities needed
to discover multicast membership and source information, build
multicast distribution trees and/or multicast transport
tunnels.
The SDN Multicast Control plane in the full multicast SDN model
Must include the following functionalities:
- Unicast topology discovery interconnecting MSEs, MBGs, MSNs
and CNs
- Multicast topology discovery including MSEs, MSNs, MBGs, and
CNs enabled for multicast
- Resource utilization monitoring on links and nodes
- Multicast group membership discovery and maintenance
- Multicast source discovery and maintenance
- Multicast distribution tree creation and maintenance
- Multicast path selection, instantiation, maintenance and
failover
- Multicast forwarding programmability
The SDN Multicast control plane SHOULD include the following
functionalities
- Entitlement admission control
- Bandwidth Admission control
8.2.1. Unicast Topology Discovery
The unicast Topology is needed to discover reachability among
MSEs, MSNs and MBGs for MSN selection or MBG selection. In
addition, the unicast topology will be needed if traffic is to
be carried using any unicast tunneling technology (IP, MPLS, SR
with IP or MPLS data planes), or pt-to-pt RSVP-TE. In this
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latter case the TE tunnels may be computed by the underlying
router. Alternatively, the TE tunnels paths MAY be computed by the
SDN controller. The same may apply for Traffic engineered SR
paths. The SDN control plane SHOULD always maintain a database of
these TE tunnels/paths and associated capacity, irrespective
how they are computed, enabling the SDN controller to
selectively bind multicast traffic to TE paths. The SDN
multicast control plane and network elements that will be used
to learn the unicast topology SHOULD support BGP-LS [RFC 7752] or
YANG topology data models [Yang-Topology-Model]. The SDN control
plane SHOULD learn the unicast topology via BGP-LS or YANG from
the network nodes. The SDN controller MUST also learn TES
reachability via MSEs using same mechanisms.
8.2.2. Multicast Topology Discovery
The SDN multicast control plane MUST have knowledge of all the
MSNs, MBGs and MSEs and their multicast resources. In case the
core network is also enabled for multicast and the SDN control
plane is to compute multicast trees, the SDN control plane MUST
know which nodes are enabled for multicast forwarding and
enabled for PIM. The Multicast topology is used by the
multicast SDN control plane to select MSNs and MBGs and to
compute multicast tree paths. The multicast tree could be based
on native IP multicast or pt-to-mpt RSVP-TE. The SDN multicast
control plane MUST maintain the computed paths and the
receivers and senders mapped to them.
8.2.3. Resource Utilization Monitoring
The SDN control plane MUST maintain knowledge of the available
resources on the nodes that may be impacted resource-wise by
being on multicast paths selected by the SDN controller. For
instance, the SDN controller MUST maintain the available
resources for multicast forwarding entries on MSEs, MSNs and
MBGs. In addition, if bandwidth and link utilization is to be
considered as part of the path selection, the SDN controller
MUST maintain knowledge of the utilization on network links.
8.2.4. Multicast Group Membership Discovery
The SDN Controller MUST learns via the MApp-C management
interfaces or the MSE-C/MTTES-C interfaces the receivers and
senders for each multicast group or channel.
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When the list of multicast receivers and senders for each
multicast group in a tenant network is known in advance and
when multicast session establishment (set of senders and
receivers for a multicast group) can be set up ahead of time of
actual multicast data delivery, applications can use the
multicast SDN controller northbound interface (MApp-C) to
populate the list of receivers and senders for the multicast
group in the SDN controller. The SDN controller may also have
access to a database, or be programmed with information via
MApp-C, that associates the receivers and senders with MSEs.
8.2.5. Multicast Sender Discovery
The multicast SDN controller MUST learn the set of senders for
each multicast group. This information May be learned via the
MSE-C/MTTES-C interfaces from MSEs or TESs, or via the MApp-C
interface from a management application. The SDN controller
could obtain the location of the sender (which MSE a sender is
connected to) from routing information, or via MApp-C and MSE-C
interfaces.
8.2.6. Multicast Distribution Tree Creation and Maintenance
The SDN controller MUST be able to compute a multicast
distribution tree. There could be several segments for a
multicast distribution tree depending on the capabilities
of the network elements, and/or the operator design. Following
are the distribution tree types:
1- Distribution Tree Type 1: The distribution tree is rooted at
one MSN that receives a multicast group source traffic from
an MSE. Then, that MSN encapsulates the multicast traffic
with a unicast tunneling header to other MSNs connected to
MSEs with receiver TESs for that group, and to other MBGs to
reach TES receivers in other domains.
2- Distribution Tree Type 2: The distribution Tree is rooted at
one MSN that receives a multicast group source traffic from
an MSE. Then, the MSN encapsulates the traffic with a
multicast tunneling header or in a multicast tunnel with
leaves being other MSNs and MBGs to reach receivers. When an
MSN receives the tenant multicast traffic on a multicast
tunnel/encapsulated in a multicast tunneling header, it
decapsulates the tenant multicast packets and unicast tunnel
them to the MSEs with receiver TESs for that group.
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In computing the multicast tree, the SDN controller SHOULD take
into account constraints on bandwidth and other QoS parameters
such as latency, jitter and packet loss in addition to the
capabilities of the forwarding plane elements (e.g., native
multicast replication support, multicast replication over
unicast tunnels, number of multicast entries, bandwidth, etc.)
and policies (e.g., which MSN is to serve which MSE, inter-SDN
domain policies etc.). A multicast distribution tree is
recomputed every time that there is a new edge node (MSE, MSN
or MBG) to be added to the multicast tree, or there is an edge
node that needs to be pruned out of the multicast tree), adding
or removing multicast branches to/from the tree.
An SDN multicast controller can map tenant overlay multicast
group addresses 1:1 to distinct multicast group addresses in
native IP multicast underlay, and program MSNs and MBGs with
the appropriate forwarding information. An SDN multicast
controller can alternatively map each designated set of tenant
overlay multicast group addresses to a unique underlay
multicast IP address and accordingly program MSNs and MBGs with
the appropriate forwarding information. In this latter case,
these tenant overlay multicast groups are aggregated into
distinct multicast group address(es) similar to mechanisms in
Default or Data MDTs (Multicast Distribution Trees) [RFC 6037].
This aggregation technique can help minimize multicast routing
states in native multicast network.
8.2.7. Multicast Forwarding Programmability
Subsequent to the (re-) computation of the multicast tree, the
SDN multicast controller MUST be able to program the multicast
forwarding entries on the forwarding elements: MSE, MSN and
MBG. When supporting dynamic receivers and senders, multicast
tree (re-)computation and programmability must be done
relatively fast so that it does not impact the user experience,
creating a significant delay in starting to receive a multicast
channel that the user joins. In other cases, multicast receiver
applications may also have a requirement on the latency between
sending a join to a multicast channel and starting to receive
data on that channel. Among other things, forwarding
programmability SHOULD enable setting the TTL treatment
behavior. Specifically, an ingress MBG SHOULD be configurable
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not to copy the Time to Live (TTL) field from SDN overlay
multicast packets. Operators should take account of the
end-to-end network topology and set the TTL field accordingly.
8.2.8. Entitlement Admission Control
When this function is enabled for a given tenant, the SDN
multicast controller checks if the requesting receiver is
entitled to receive the content of the multicast group/channel
it is requesting to join. The SDN controller MAY be programmed
with the list of receivers that are allowed to receive traffic
from certain source(s), and whereby the receivers may be
identified by IP host addresses, IP subnets or other types of
identifiers. This entitlement information can be configured on
the controller or it may be available through some database or
system that has that information.
8.2.9. Bandwidth Admission Control
Bandwidth admission control prevents content or subscription
overload from senders or receivers as well as provides
important security protection by putting upper limits on how
much traffic each sender or receiver can send or subscribe to.
When this function is enabled, the SDN multicast controller
may perform bandwidth admission control when permitting a
channel to be delivered to a TES and/or when selecting the
multicast channel path. The specification of bandwidth
admission control mechanisms is beyond the scope of this
framework.
8.3. Multicast Functional Components Implementation
MSE, MSN and MBG are functional components that may be co-
located on the same router and implemented in different forms
(physical, virtual, or applications). For example, MSEs and
MSNs can co-locate together in the same physical or virtual
router.
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8.4. SDN Multicast Management Interfaces
8.4.1. North-Bound Interface
MApp-C is a northbound interface from the SDN controller that
provides management applications the means to interact with the
SDN controller to set and extract multicast configurations and
information, respectively. It is independent of individual
network devices, vendors or device types. MApp-C interface
SHOULD provide a comprehensive and flexible data model and
messaging methods that allow these applications to access
Multicast SDN Controllers to request the addition or removal of
a receiver to a multicast (S,G) channel, the establishment of a
multicast distribution tree between specified senders and
receivers with potential constraints on bandwidth and QoS for
instance, set entitlement rules, and obtain state information
pertinent to a multicast group or participants in that multicast
group among others. Applications SHOULD have a means to perform
these actions across MSDs, each with an SDN controller, with one
action rather than separate actions initiated with each of the
MSD controllers.
8.4.2. Multicast SDN Functional Component Facing Interfaces
MTTES-C, MSE-C, MSN-C, MBG-C are interfaces between a Multicast
SDN Controller on one hand and TESs and Multicast
SDN forwarding functional components on the other hand. Each
interface is specific to the associated functional component,
and is used to provide control plane and/or data plane
programming of that component and to harness information from
that component.
8.4.3. Traditional Underlay Network Element Interfaces
CN-C is the interface between Multicast SDN controller and core
network elements that provide core forwarding services, as
opposed to edge services provided by MSE, MSN and MBG. The
purpose of CN-C is to provide for programming of network
elements in the core whenever it is possible or necessary, and
to extract operational state information from these elements.
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8.4.4. Information Model and Data Model of Management Interfaces
Both northbound interface and SDN functional component facing
interfaces SHOULD be based on RESTCONF [RESTCONF] or
NETCONF [RFC6241]. Their data models should be based on YANG.
9. SDN Control Plane
The SDN Control plane can be composed of one or more
controllers. These controllers will need to cooperate in the
establishment of a multicast distribution tree within MSDs and
across MSDs. How they cooperate or interact is dependent on the
relationship relative to MSDs, ASes, and administrative
entities (operators). In this section, the following cases are
considered:
1- Intra-MSD, Inter-SDN Controller Interactions
2- Inter-MSD, Intra-AS, Inter-SDN Controller Interactions
3- Inter-MSD, Inter-AS, Intra-operator, Inter-SDN Controller
Interactions
4- Inter-MSD, Inter-AS, Inter-operator, Inter-SDN Controller
Interactions
(this section will be completed in a future update).
10. Multi-Party Multicast SDN Overlay Interaction
If multicast senders and receivers are on different multicast
SDN overlay vendor solutions, it SHOULD be possible to setup
and exchange multicast control states as well as underlying
tunneling information.
11. Security Considerations
Following are the security considerations that pertain to the
multicast SDN framework in this document:
1- The communication channel between any data element and the
SDN controller MUST be trusted and secure, with mutual
authentication. This applies to all interfaces (MSE-C, MSN-C,
CN-C, MTTES-C and MBG-C) in order is to prevent rogue
controllers from hijacking multicast traffic, mounting
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security attacks on network elements or leaking tenant
multicast traffic to other tenants.
2- MSE must have means to cope with tenant end systems
misbehavior, malicious or malfunctioning, that may result in
control plane attack on the SDN controller, impacting the
stability of the system and as a result impacting multicast
services. The MSE MUST be able to limit the message rate that
could be triggered by tenant end system activity, and the
controller MUST be able to limit message rate and routing
activity changes at the tenant level as that could result in
a DDOS on the multicast services across tenants.
3- The association between a TES and tenant network must be
authentic so that traffic eavesdropping is prevented and a
TES is not allowed to illegally inject multicast traffic into
another tenant network.
4- The SDN controller SHOULD have the means to authorize a TES
to join a multicast channel (entitlement).
5- The SDN controller SHOULD have the means to exercise
admission control to avoid congestion on network links as
causing congestion could be a way to launch a DDOS.
12. IANA Considerations
The document does not require any IANA action.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
13.2. Informative References
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B. and
A. Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[EDGE-REP] Marques P. et al., "Edge multicast replication for
BGP IP VPNs", draft-marques-l3vpn-mcast-edge-01, work in
progress, June 2012.
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[RFC 6037] E. Rosen, Y. Cai, I. Wijnands, "Cisco Systems
Solution for Multicast in BGP/MPLS IP VPNs", RFC 6037.
October 2010.
[RFC 6513] E. Rosen E., et al. , "Multicast in MPLS/BGP IP VPNs",
RFC 6513, February 2012.
[IGMP-EVPN] A. Sajassi, et al., "IGMP and MLD Proxy for EVPN",
draft-sajassi-bess-evpn-igmp-mld-proxy-00, October 17, 2015.
[RFC 7716] Z. Zhang, L. Giuliano, E. Rosen, et al., "Global
Table Multicast with BGP Multicast VPN (BGP-MVPN) Procedures",
RFC 7716, December 2015.
[BIER-ARCH] IJ. Wijnands, et al. "Multicast using Bit Index
Explicit Replication", draft-ietf-bier-architecture-04, July
18, 2016.
[SR-ARCH] C. Filsfils, et al, "Segment Routing Architecture",
draft-ietf-spring-segment-routing-11, February 16, 2017.
[Yang-Topology-Model] A. Clemm, e al., "A Data Model for Network
Topologies", draft-ietf-i2rs-yang-network-topo-12, March 1, 2017.
[RFC 7752] H. Greedier, et al., "North-Bound Distribution of
Link-State and Traffic Engineering (TE) Information Using BGP",
RFC 7752, March 2016.
[RFC 6241] R. Enns, et al., "Network Configuration Protocol
(NETCONF)", RFC 6241, June 2011.
[RESTCONF] A. Bierman, M. Bjorklund, K. Watsen, "RESTCONF
Protocol", draft-ietf-netconf-restconf-17, September 28, 2016.
[NVO3-MCAST] A. Ghanwani, et al., "A Framework for Multicast in
Network Virtualization Overlays", draft-ietf-nvo3-mcast-
framework-05, May 9, 2016.
[LISP] D. Farinacci, et al., "The Locator/ID Separation
Protocol (LISP)", RFC 6830, January 2013.
[LISP-mcst] D. Farinacci, et al., "The Locator/ID Separation
Protocol (LISP) for Multicast Environments", RFC 6831,
January 2013.
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14. Acknowledgments
The authors thank Dino Farinacci for his comments and input.
Authors Addresses
David Qi
Bloomberg
EMail: dqi@bloomberg.net
Nabil Bitar
Nokia
EMail: nabil.bitar@nokia.com
Truman Boyes
Bloomberg
EMail: tboyes@bloomberg.net
Senad Palislamovic
Nokia
EMail: senad.palislamovic@nokia.com
Anil Lohiya
Juniper
EMail: alohiya@juniper.net
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