Internet DRAFT - draft-kumar-bier-use-cases
draft-kumar-bier-use-cases
Network Working Group N. Kumar
Internet-Draft R. Asati
Intended status: Informational Cisco
Expires: August 13, 2015 M. Chen
X. Xu
Huawei
A. Dolganow
Alcatel-Lucent
T. Przygienda
Ericsson
A. Gulko
Thomson Reuters
D. Robinson
id3as-company Ltd
February 9, 2015
BIER Use Cases
draft-kumar-bier-use-cases-02.txt
Abstract
Bit Index Explicit Replication (BIER) is an architecture that
provides optimal multicast forwarding through a "BIER domain" without
requiring intermediate routers to maintain any multicast related per-
flow state. BIER also does not require any explicit tree-building
protocol for its operation. A multicast data packet enters a BIER
domain at a "Bit-Forwarding Ingress Router" (BFIR), and leaves the
BIER domain at one or more "Bit-Forwarding Egress Routers" (BFERs).
The BFIR router adds a BIER header to the packet. The BIER header
contains a bit-string in which each bit represents exactly one BFER
to forward the packet to. The set of BFERs to which the multicast
packet needs to be forwarded is expressed by setting the bits that
correspond to those routers in the BIER header.
This document describes some of the use-cases for BIER.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on August 13, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . 3
3. BIER Use Cases . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Multicast in L3VPN Networks . . . . . . . . . . . . . . . 3
3.2. BUM in EVPN . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. IPTV and OTT Services . . . . . . . . . . . . . . . . . . 5
3.4. Multi-service, converged L3VPN network . . . . . . . . . 6
3.5. Control-plane simplification and SDN-controlled networks 7
3.6. Data center Virtualization/Overlay . . . . . . . . . . . 7
3.7. Financial Services . . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Bit Index Explicit Replication (BIER)
[I-D.wijnands-bier-architecture] is an architecture that provides
optimal multicast forwarding through a "BIER domain" without
requiring intermediate routers to maintain any multicast related per-
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flow state. BIER also does not require any explicit tree-building
protocol for its operation. A multicast data packet enters a BIER
domain at a "Bit-Forwarding Ingress Router" (BFIR), and leaves the
BIER domain at one or more "Bit-Forwarding Egress Routers" (BFERs).
The BFIR router adds a BIER header to the packet. The BIER header
contains a bit-string in which each bit represents exactly one BFER
to forward the packet to. The set of BFERs to which the multicast
packet needs to be forwarded is expressed by setting the bits that
correspond to those routers in the BIER header.
The obvious advantage of BIER is that there is no per flow multicast
state in the core of the network and there is no tree building
protocol that sets up tree on demand based on users joining a
multicast flow. In that sense, BIER is potentially applicable to
many services where Multicast is used and not limited to the examples
described in this draft. In this document we are describing a few
use-cases where BIER could provide benefit over using existing
mechanisms.
2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. BIER Use Cases
3.1. Multicast in L3VPN Networks
The Multicast L3VPN architecture [RFC6513] describes many different
profiles in order to transport L3 Multicast across a providers
network. Each profile has its own different tradeoffs (see section
2.1 [RFC6513]). When using "Multidirectional Inclusive" "Provider
Multicast Service Interface" (MI-PMSI) an efficient tree is build per
VPN, but causes flooding of egress PE's that are part of the VPN, but
have not joined a particular C-multicast flow. This problem can be
solved with the "Selective" PMSI to build a special tree for only
those PE's that have joined the C-multicast flow for that specific
VPN. The more S-PMSI's, the less bandwidth is wasted due to
flooding, but causes more state to be created in the providers
network. This is a typical problem network operators are faced with
by finding the right balance between the amount of state carried in
the network and how much flooding (waste of bandwidth) is acceptable.
Some of the complexity with L3VPN's comes due to providing different
profiles to accommodate these trade-offs.
With BIER there is no trade-off between State and Flooding. Since
the receiver information is explicitly carried within the packet,
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there is no need to build S-PMSI's to deliver multicast to a sub-set
of the VPN egress PE's. Due to that behaviour, there is no need for
S-PMSI's.
Mi-PMSI's and S-PMSI's are also used to provide the VPN context to
the Egress PE router that receives the multicast packet. Also, in
some MVPN profiles it is also required to know which Ingress PE
forwarded the packet. Based on the PMSI the packet is received from,
the target VPN is determined. This also means there is a requirement
to have a least a PMSI per VPN or per VPN/Ingress PE. This means the
amount of state created in the network is proportional to the VPN and
ingress PE's. Creating PMSI state per VPN can be prevented by
applying the procedures as documented in [RFC5331]. This however has
not been very much adopted/implemented due to the excessive flooding
it would cause to Egress PE's since *all* VPN multicast packets are
forwarded to *all* PE's that have one or more VPN's attached to it.
With BIER, the destination PE's are identified in the multicast
packet, so there is no flooding concern when implementing [RFC5331].
For that reason there is no need to create multiple BIER domain's per
VPN, the VPN context can be carry in the multicast packet using the
procedures as defined in [RFC5331]. Also see
[I-D.rosen-l3vpn-mvpn-bier] for more information.
With BIER only a few MVPN profiles will remain relevant, simplifying
the operational cost and making it easier to be interoperable among
different vendors.
3.2. BUM in EVPN
The current widespread adoption of L2VPN services [RFC4664],
especially the upcoming EVPN solution [I-D.ietf-l2vpn-evpn] which
transgresses many limitations of VPLS, introduces the need for an
efficient mechanism to replicate broadcast, unknown and multicast
(BUM) traffic towards the PEs that participate in the same EVPN
instances (EVIs). As simplest deployable mechanism, ingress
replication is used but poses accordingly a high burden on the
ingress node as well as saturating the underlying links with many
copies of the same frame headed to different PEs. Fortunately
enough, EVPN signals internally P-Multicast Service Interface (PMSI)
[RFC6513] attribute to establish transport for BUM frames and with
that allows to deploy a plethora of multicast replication services
that the underlying network layer can provide. It is therefore
relatively simple to deploy BIER P-Tunnels for EVPN and with that
distribute BUM traffic without building of P-router state in the core
required by PIM, mLDP or comparable solutions.
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Specifically, the same I-PMSI attribute suggested for mVPN can be
used easily in EVPN and given EVPN can multiplex and disassociate BUM
frames on p2mp and mp2mp trees using upstream assigned labels, BIER
P-Tunnel will support BUM flooding for any number of EVIs over a
single sub-domain for maximum scalability but allow at the other
extreme of the spectrum to use a single BIER sub-domain per EVI if
such a deployment is necessary.
Multiplexing EVIs onto the same PMSI forces the PMSI to span more
than the necessary number of PEs normally, i.e. the union of all PEs
participating in the EVIs multiplexed on the PMSI. Given the
properties of BIER it is however possible to encode in the receiver
bitmask only the PEs that participate in the EVI the BUM frame
targets. In a sense BIER is an inclusive as well as a selective tree
and can allow to deliver the frame to only the set of receivers
interested in a frame even though many others participate in the same
PMSI.
As another significant advantage, it is imaginable that the same BIER
tunnel needed for BUM frames can optimize the delivery of the
multicast frames though the signaling of group memberships for the
PEs involved has not been specified as of date.
3.3. IPTV and OTT Services
IPTV is a service, well known for its characteristics of allowing
both live and on-demand delivery of media traffic over end-to-end
Managed IP network.
Over The Top (OTT) is a similar service, well known for its
characteristics of allowing live and on-demand delivery of media
traffic between IP domains, where the source is often on an external
network relative to the receivers.
Content Delivery Networks (CDN) operators provide layer 4
applications, and often some degree of managed layer 3 IP network,
that enable media to be securely and reliably delivered to many
receivers. In some models they may place applications within third
party networks, or they may place those applications at the edges of
their own managed network peerings and similar inter-domain
connections. CDNs provide capabilities to help publishers scale to
meet large audience demand. Their applications are not limited to
audio and video delivery, but may include static and dynamic web
content, or optimized delivery for Massive Multiplayer Gaming and
similar. Most publishers will use a CDN for public Internet
delivery, and some publishers will use a CDN internally within their
IPTV networks to resolve layer 4 complexity.
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In a typical IPTV environment the egress routers connecting to the
receivers will build the tree towards the ingress router connecting
to the IPTV servers. The egress routers would rely on IGMP/MLD
(static or dynamic) to learn about the receiver's interest in one or
more multicast group/channels. Interestingly, BIER could allows
provisioning any new multicast group/channel by only modifying the
channel mapping on ingress routers. This is deemed beneficial for
the linear IPTV video broadcasting in which every receivers behind
every egress PE routers would receive the IPTV video traffic.
With BIER in IPTV environment, there is no need of tree building from
egress to ingress. Further, any addition of new channel or new
egress routers can be directly controlled from ingress router. When
a new channel is included, the multicast group is mapped to Bit
string that includes all egress routers. Ingress router would start
sending the new channel and deliver it to all egress routers. As it
can be observed, there is no need for static IGMP provisioning in
each egress routers whenever a new channel/stream is added. Instead,
it can be controlled from ingress router itself by configuring the
new group to Bit Mask mapping on ingress router.
With BIER in OTT environment, these edge routers in CDN domain
terminating the OTT user session connect to the Ingress BIER routers
connecting content provider domains or a local cache server and
leverage the scalability benefit that BIER could provide. This may
rely on MBGP interoperation (or similar) between the egress of one
domain and the ingress of the next domain, or some other SDN control
plane may prove a more effective and simpler way to deploy BIER. For
a single CDN operator this could be well managed in the Layer 4
applications that they provide and it may be that the initial
receiver in a remote domain is actually an application operated by
the CDN which in turn acts as a source for the Ingress BIER router in
that remote domain, and by doing so keeps the BIER more descrete on a
domain by domain basis.
3.4. Multi-service, converged L3VPN network
Increasingly operators deploy single networks for multiple-services.
For example a single Metro Core network could be deployed to provide
Residential IPTV retail service, residential IPTV wholesale service,
and business L3VPN service with multicast. It may often be desired
by an operator to use a single architecture to deliver multicast for
all of those services. In some cases, governing regulations may
additionally require same service capabilities for both wholesale and
retail multicast services. To meet those requirements, some
operators use multicast architecture as defined in [RFC5331].
However, the need to support many L3VPNs, with some of those L3VPNs
scaling to hundreds of egress PE's and thousands of C-multicast
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flows, make scaling/efficiency issues defined in earlier sections of
this document even more prevalent. Additionally support for ten's of
millions of BGP multicast A-D and join routes alone could be required
in such networks with all consequences such a scale brings.
With BIER, again there is no need of tree building from egress to
ingress for each L3VPN or individual or group of c-multicast flows.
As described earlier on, any addition of a new IPTV channel or new
egress router can be directly controlled from ingress router and
there is no flooding concern when implementing [RFC5331].
3.5. Control-plane simplification and SDN-controlled networks
With the advent of Software Defined Networking, some operators are
looking at various ways to reduce the overall cost of providing
networking services including multicast delivery. Some of the
alternatives being consider include minimizing capex cost through
deployment of network-elements with simplified control plane
function, minimizing operational cost by reducing control protocols
required to achieve a particular service, etc. Segment routing as
described in [I-D.ietf-spring-segment-routing] provides a solution
that could be used to provide simplified control-plane architecture
for unicast traffic. With Segment routing deployed for unicast, a
solution that simplifies control-plane for multicast would thus also
be required, or operational and capex cost reductions will not be
achieved to their full potential.
With BIER, there is no longer a need to run control protocols
required to build a distribution tree. If L3VPN with multicast, for
example, is deployed using [RFC5331] with MPLS in P-instance, the
MPLS control plane would no longer be required. BIER also allows
migration of C-multicast flows from non-BIER to BIER-based
architecture, which makes transition to control-plane simplified
network simpler to operationalize. Finally, for operators, who would
desire centralized, offloaded control plane, multicast overlay as
well as BIER forwarding could migrate to controller-based
programming.
3.6. Data center Virtualization/Overlay
Virtual eXtensible Local Area Network (VXLAN) [RFC7348] is a kind of
network virtualization overlay technology which is intended for
multi-tenancy data center networks. To emulate a layer2 flooding
domain across the layer3 underlay, it requires to have a mapping
between the VXLAN Virtual Network Instance (VNI) and the IP multicast
group in a ratio of 1:1 or n:1. In other words, it requires to
enable the multicast capability in the underlay. For instance, it
requires to enable PIM-SM [RFC4601] or PIM-BIDIR [RFC5015] multicast
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routing protocol in the underlay. VXLAN is designed to support 16M
VNIs at maximum. In the mapping ratio of 1:1, it would require 16M
multicast groups in the underlay which would become a significant
challenge to both the control plane and the data plane of the data
center switches. In the mapping ratio of n:1, it would result in
inefficiency bandwidth utilization which is not optimal in data
center networks. More importantly, it is recognized by many data
center operators as a unaffordable burden to run multicast in data
center networks from network operation and maintenance perspectives.
As a result, many VXLAN implementations are claimed to support the
ingress replication capability since ingress replication eliminates
the burden of running multicast in the underlay. Ingress replication
is an acceptable choice in small-sized networks where the average
number of receivers per multicast flow is not too large. However, in
multi-tenant data center networks, especially those in which the NVE
functionality is enabled on a high amount of physical servers, the
average number of NVEs per VN instance would be very large. As a
result, the ingress replication scheme would result in a serious
bandwidth waste in the underlay and a significant replication burden
on ingress NVEs.
With BIER, there is no need for maintaining that huge amount of
multicast states in the underlay anymore while the delivery
efficiency of overlay BUM traffic is the same as if any kind of
stateful multicast protocols such as PIM-SM or PIM-BIDIR is enabled
in the underlay.
3.7. Financial Services
Financial services extensively rely on IP Multicast to deliver stock
market data and its derivatives, and critically require optimal
latency path (from publisher to subscribers), deterministic
convergence (so as to deliver market data derivatives fairly to each
client) and secured delivery.
Current multicast solutions e.g. PIM, mLDP etc., however, don't
sufficiently address the above requirements. The reason is that the
current solutions are primarily subscriber driven i.e. multicast tree
is setup using reverse path forwarding techniques, and as a result,
the chosen path for market data may not be latency optimal from
publisher to the (market data) subscribers.
As the number of multicast flows grows, the convergence time might
increase and make it somewhat nondeterministic from the first to the
last flow depending on platforms/implementations. Also, by having
more protocols in the network, the variability to ensure secured
delivery of multicast data increases, thereby undermining the overall
security aspect.
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BIER enables setting up the most optimal path from publisher to
subscribers by leveraging unicast routing relevant for the
subscribers. With BIER, the multicast convergence is as fast as
unicast, uniform and deterministic regardless of number of multicast
flows. This makes BIER a perfect multicast technology to achieve
fairness for market derivatives per each subscriber.
4. Security Considerations
There are no security issues introduced by this draft.
5. IANA Considerations
There are no IANA consideration introduced by this draft.
6. Acknowledgments
The authors would like to thank IJsbrand Wijnands, Greg Shepherd and
Christian Martin for their contribution.
7. References
7.1. Normative References
[I-D.rosen-l3vpn-mvpn-bier]
Rosen, E., Sivakumar, M., Wijnands, I., Aldrin, S.,
Dolganow, A., and T. Przygienda, "Multicast VPN Using
BIER", draft-rosen-l3vpn-mvpn-bier-02 (work in progress),
December 2014.
[I-D.wijnands-bier-architecture]
Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
S. Aldrin, "Multicast using Bit Index Explicit
Replication", draft-wijnands-bier-architecture-04 (work in
progress), February 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
[I-D.ietf-l2vpn-evpn]
Sajassi, A., Aggarwal, R., Bitar, N., Isaac, A., and J.
Uttaro, "BGP MPLS Based Ethernet VPN", draft-ietf-l2vpn-
evpn-11 (work in progress), October 2014.
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[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
and E. Crabbe, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-01 (work in progress), February
2015.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4664] Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
Private Networks (L2VPNs)", RFC 4664, September 2006.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, October 2007.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space", RFC
5331, August 2008.
[RFC6513] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP
VPNs", RFC 6513, February 2012.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, August 2014.
Authors' Addresses
Nagendra Kumar
Cisco
7200 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: naikumar@cisco.com
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Rajiv Asati
Cisco
7200 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: rajiva@cisco.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
Xiaohu Xu
Huawei
Email: xuxiaohu@huawei.com
Andrew Dolganow
Alcatel-Lucent
600 March Road
Ottawa, ON K2K2E6
Canada
Email: andrew.dolganow@alcatel-lucent.com
Tony Przygienda
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: antoni.przygienda@ericsson.com
Arkadiy Gulko
Thomson Reuters
195 Broadway
New York NY 10007
USA
Email: arkadiy.gulko@thomsonreuters.com
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Dom Robinson
id3as-company Ltd
UK
Email: Dom@id3as.co.uk
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