Network Working Group N. Kumar
Internet-Draft R. Asati
Intended status: Informational Cisco
Expires: April 28, 2015 M. Chen
X. Xu
Huawei
October 25, 2014
BIER Use Cases
draft-kumar-bier-use-cases-00.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.
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This Internet-Draft will expire on April 28, 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. IPTV Services . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Data center Virtualization/Overlay . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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-
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.
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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,
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
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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. IPTV Services
IPTV is a service, well known for its characteristics of allowing
both live and on-demand delivery of media traffic over IP. 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, 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.
3.3. 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
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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
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.
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.
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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-01 (work in progress),
October 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-01 (work in
progress), October 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 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
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Nagendra Kumar
Cisco
7200 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: naikumar@cisco.com
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
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