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Versions: 00 01 02 03
MBONED M. McBride
Internet-Draft Huawei
Intended status: Informational O. Komolafe
Expires: December 31, 2018 Arista Networks
June 29, 2018
Multicast in the Data Center Overview
draft-ietf-mboned-dc-deploy-03
Abstract
The volume and importance of one-to-many traffic patterns in data
centers is likely to increase significantly in the future. Reasons
for this increase are discussed and then attention is paid to the
manner in which this traffic pattern may be judiously handled in data
centers. The intuitive solution of deploying conventional IP
multicast within data centers is explored and evaluated. Thereafter,
a number of emerging innovative approaches are described before a
number of recommendations are made.
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-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 31, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Reasons for increasing one-to-many traffic patterns . . . . . 3
2.1. Applications . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Overlays . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Protocols . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Handling one-to-many traffic using conventional multicast . . 5
3.1. Layer 3 multicast . . . . . . . . . . . . . . . . . . . . 6
3.2. Layer 2 multicast . . . . . . . . . . . . . . . . . . . . 6
3.3. Example use cases . . . . . . . . . . . . . . . . . . . . 8
3.4. Advantages and disadvantages . . . . . . . . . . . . . . 9
4. Alternative options for handling one-to-many traffic . . . . 9
4.1. Minimizing traffic volumes . . . . . . . . . . . . . . . 9
4.2. Head end replication . . . . . . . . . . . . . . . . . . 10
4.3. BIER . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4. Segment Routing . . . . . . . . . . . . . . . . . . . . . 12
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The volume and importance of one-to-many traffic patterns in data
centers is likely to increase significantly in the future. Reasons
for this increase include the nature of the traffic generated by
applications hosted in the data center, the need to handle broadcast,
unknown unicast and multicast (BUM) traffic within the overlay
technologies used to support multi-tenancy at scale, and the use of
certain protocols that traditionally require one-to-many control
message exchanges. These trends, allied with the expectation that
future highly virtualized data centers must support communication
between potentially thousands of participants, may lead to the
natural assumption that IP multicast will be widely used in data
centers, specifically given the bandwidth savings it potentially
offers. However, such an assumption would be wrong. In fact, there
is widespread reluctance to enable IP multicast in data centers for a
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number of reasons, mostly pertaining to concerns about its
scalability and reliability.
This draft discusses some of the main drivers for the increasing
volume and importance of one-to-many traffic patterns in data
centers. Thereafter, the manner in which conventional IP multicast
may be used to handle this traffic pattern is discussed and some of
the associated challenges highlighted. Following this discussion, a
number of alternative emerging approaches are introduced, before
concluding by discussing key trends and making a number of
recommendations.
1.1. Requirements Language
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 RFC 2119.
2. Reasons for increasing one-to-many traffic patterns
2.1. Applications
Key trends suggest that the nature of the applications likely to
dominate future highly-virtualized multi-tenant data centers will
produce large volumes of one-to-many traffic. For example, it is
well-known that traffic flows in data centers have evolved from being
predominantly North-South (e.g. client-server) to predominantly East-
West (e.g. distributed computation). This change has led to the
consensus that topologies such as the Leaf/Spine, that are easier to
scale in the East-West direction, are better suited to the data
center of the future. This increase in East-West traffic flows
results from VMs often having to exchange numerous messages between
themselves as part of executing a specific workload. For example, a
computational workload could require data, or an executable, to be
disseminated to workers distributed throughout the data center which
may be subsequently polled for status updates. The emergence of such
applications means there is likely to be an increase in one-to-many
traffic flows with the increasing dominance of East-West traffic.
The TV broadcast industry is another potential future source of
applications with one-to-many traffic patterns in data centers. The
requirement for robustness, stability and predicability has meant the
TV broadcast industry has traditionally used TV-specific protocols,
infrastructure and technologies for transmitting video signals
between cameras, studios, mixers, encoders, servers etc. However,
the growing cost and complexity of supporting this approach,
especially as the bit rates of the video signals increase due to
demand for formats such as 4K-UHD and 8K-UHD, means there is a
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consensus that the TV broadcast industry will transition from
industry-specific transmission formats (e.g. SDI, HD-SDI) over TV-
specific infrastructure to using IP-based infrastructure. The
development of pertinent standards by the SMPTE, along with the
increasing performance of IP routers, means this transition is
gathering pace. A possible outcome of this transition will be the
building of IP data centers in broadcast plants. Traffic flows in
the broadcast industry are frequently one-to-many and so if IP data
centers are deployed in broadcast plants, it is imperative that this
traffic pattern is supported efficiently in that infrastructure. In
fact, a pivotal consideration for broadcasters considering
transitioning to IP is the manner in which these one-to-many traffic
flows will be managed and monitored in a data center with an IP
fabric.
Arguably one of the (few?) success stories in using conventional IP
multicast has been for disseminating market trading data. For
example, IP multicast is commonly used today to deliver stock quotes
from the stock exchange to financial services provider and then to
the stock analysts or brokerages. The network must be designed with
no single point of failure and in such a way that the network can
respond in a deterministic manner to any failure. Typically,
redundant servers (in a primary/backup or live-live mode) send
multicast streams into the network, with diverse paths being used
across the network. Another critical requirement is reliability and
traceability; regulatory and legal requirements means that the
producer of the marketing data must know exactly where the flow was
sent and be able to prove conclusively that the data was received
within agreed SLAs. The stock exchange generating the one-to-many
traffic and stock analysts/brokerage that receive the traffic will
typically have their own data centers. Therefore, the manner in
which one-to-many traffic patterns are handled in these data centers
are extremely important, especially given the requirements and
constraints mentioned.
Many data center cloud providers provide publish and subscribe
applications. There can be numerous publishers and subscribers and
many message channels within a data center. With publish and
subscribe servers, a separate message is sent to each subscriber of a
publication. With multicast publish/subscribe, only one message is
sent, regardless of the number of subscribers. In a publish/
subscribe system, client applications, some of which are publishers
and some of which are subscribers, are connected to a network of
message brokers that receive publications on a number of topics, and
send the publications on to the subscribers for those topics. The
more subscribers there are in the publish/subscribe system, the
greater the improvement to network utilization there might be with
multicast.
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2.2. Overlays
The proposed architecture for supporting large-scale multi-tenancy in
highly virtualized data centers [RFC8014] consists of a tenant's VMs
distributed across the data center connected by a virtual network
known as the overlay network. A number of different technologies
have been proposed for realizing the overlay network, including VXLAN
[RFC7348], VXLAN-GPE [I-D.ietf-nvo3-vxlan-gpe], NVGRE [RFC7637] and
GENEVE [I-D.ietf-nvo3-geneve]. The often fervent and arguably
partisan debate about the relative merits of these overlay
technologies belies the fact that, conceptually, it may be said that
these overlays typically simply provide a means to encapsulate and
tunnel Ethernet frames from the VMs over the data center IP fabric,
thus emulating a layer 2 segment between the VMs. Consequently, the
VMs believe and behave as if they are connected to the tenant's other
VMs by a conventional layer 2 segment, regardless of their physical
location within the data center. Naturally, in a layer 2 segment,
point to multi-point traffic can result from handling BUM (broadcast,
unknown unicast and multicast) traffic. And, compounding this issue
within data centers, since the tenant's VMs attached to the emulated
segment may be dispersed throughout the data center, the BUM traffic
may need to traverse the data center fabric. Hence, regardless of
the overlay technology used, due consideration must be given to
handling BUM traffic, forcing the data center operator to consider
the manner in which one-to-many communication is handled within the
IP fabric.
2.3. Protocols
Conventionally, some key networking protocols used in data centers
require one-to-many communication. For example, ARP and ND use
broadcast and multicast messages within IPv4 and IPv6 networks
respectively to discover MAC address to IP address mappings.
Furthermore, when these protocols are running within an overlay
network, then it essential to ensure the messages are delivered to
all the hosts on the emulated layer 2 segment, regardless of physical
location within the data center. The challenges associated with
optimally delivering ARP and ND messages in data centers has
attracted lots of attention [RFC6820]. Popular approaches in use
mostly seek to exploit characteristics of data center networks to
avoid having to broadcast/multicast these messages, as discussed in
Section 4.1.
3. Handling one-to-many traffic using conventional multicast
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3.1. Layer 3 multicast
PIM is the most widely deployed multicast routing protocol and so,
unsurprisingly, is the primary multicast routing protocol considered
for use in the data center. There are three potential popular
flavours of PIM that may be used: PIM-SM [RFC4601], PIM-SSM [RFC4607]
or PIM-BIDIR [RFC5015]. It may be said that these different modes of
PIM tradeoff the optimality of the multicast forwarding tree for the
amount of multicast forwarding state that must be maintained at
routers. SSM provides the most efficient forwarding between sources
and receivers and thus is most suitable for applications with one-to-
many traffic patterns. State is built and maintained for each (S,G)
flow. Thus, the amount of multicast forwarding state held by routers
in the data center is proportional to the number of sources and
groups. At the other end of the spectrum, BIDIR is the most
efficient shared tree solution as one tree is built for all (S,G)s,
therefore minimizing the amount of state. This state reduction is at
the expense of optimal forwarding path between sources and receivers.
This use of a shared tree makes BIDIR particularly well-suited for
applications with many-to-many traffic patterns, given that the
amount of state is uncorrelated to the number of sources. SSM and
BIDIR are optimizations of PIM-SM. PIM-SM is still the most widely
deployed multicast routing protocol. PIM-SM can also be the most
complex. PIM-SM relies upon a RP (Rendezvous Point) to set up the
multicast tree and subsequently there is the option of switching to
the SPT (shortest path tree), similar to SSM, or staying on the
shared tree, similar to BIDIR.
3.2. Layer 2 multicast
With IPv4 unicast address resolution, the translation of an IP
address to a MAC address is done dynamically by ARP. With multicast
address resolution, the mapping from a multicast IPv4 address to a
multicast MAC address is done by assigning the low-order 23 bits of
the multicast IPv4 address to fill the low-order 23 bits of the
multicast MAC address. Each IPv4 multicast address has 28 unique
bits (the multicast address range is 224.0.0.0/12) therefore mapping
a multicast IP address to a MAC address ignores 5 bits of the IP
address. Hence, groups of 32 multicast IP addresses are mapped to
the same MAC address meaning a a multicast MAC address cannot be
uniquely mapped to a multicast IPv4 address. Therefore, planning is
required within an organization to choose IPv4 multicast addresses
judiciously in order to avoid address aliasing. When sending IPv6
multicast packets on an Ethernet link, the corresponding destination
MAC address is a direct mapping of the last 32 bits of the 128 bit
IPv6 multicast address into the 48 bit MAC address. It is possible
for more than one IPv6 multicast address to map to the same 48 bit
MAC address.
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The default behaviour of many hosts (and, in fact, routers) is to
block multicast traffic. Consequently, when a host wishes to join an
IPv4 multicast group, it sends an IGMP [RFC2236], [RFC3376] report to
the router attached to the layer 2 segment and also it instructs its
data link layer to receive Ethernet frames that match the
corresponding MAC address. The data link layer filters the frames,
passing those with matching destination addresses to the IP module.
Similarly, hosts simply hand the multicast packet for transmission to
the data link layer which would add the layer 2 encapsulation, using
the MAC address derived in the manner previously discussed.
When this Ethernet frame with a multicast MAC address is received by
a switch configured to forward multicast traffic, the default
behaviour is to flood it to all the ports in the layer 2 segment.
Clearly there may not be a receiver for this multicast group present
on each port and IGMP snooping is used to avoid sending the frame out
of ports without receivers.
IGMP snooping, with proxy reporting or report suppression, actively
filters IGMP packets in order to reduce load on the multicast router
by ensuring only the minimal quantity of information is sent. The
switch is trying to ensure the router has only a single entry for the
group, regardless of the number of active listeners. If there are
two active listeners in a group and the first one leaves, then the
switch determines that the router does not need this information
since it does not affect the status of the group from the router's
point of view. However the next time there is a routine query from
the router the switch will forward the reply from the remaining host,
to prevent the router from believing there are no active listeners.
It follows that in active IGMP snooping, the router will generally
only know about the most recently joined member of the group.
In order for IGMP and thus IGMP snooping to function, a multicast
router must exist on the network and generate IGMP queries. The
tables (holding the member ports for each multicast group) created
for snooping are associated with the querier. Without a querier the
tables are not created and snooping will not work. Furthermore, IGMP
general queries must be unconditionally forwarded by all switches
involved in IGMP snooping. Some IGMP snooping implementations
include full querier capability. Others are able to proxy and
retransmit queries from the multicast router.
Multicast Listener Discovery (MLD) [RFC 2710] [RFC 3810] is used by
IPv6 routers for discovering multicast listeners on a directly
attached link, performing a similar function to IGMP in IPv4
networks. MLDv1 [RFC 2710] is similar to IGMPv2 and MLDv2 [RFC 3810]
[RFC 4604] similar to IGMPv3. However, in contrast to IGMP, MLD does
not send its own distinct protocol messages. Rather, MLD is a
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subprotocol of ICMPv6 [RFC 4443] and so MLD messages are a subset of
ICMPv6 messages. MLD snooping works similarly to IGMP snooping,
described earlier.
3.3. Example use cases
A use case where PIM and IGMP are currently used in data centers is
to support multicast in VXLAN deployments. In the original VXLAN
specification [RFC7348], a data-driven flood and learn control plane
was proposed, requiring the data center IP fabric to support
multicast routing. A multicast group is associated with each virtual
network, each uniquely identified by its VXLAN network identifiers
(VNI). VXLAN tunnel endpoints (VTEPs), typically located in the
hypervisor or ToR switch, with local VMs that belong to this VNI
would join the multicast group and use it for the exchange of BUM
traffic with the other VTEPs. Essentially, the VTEP would
encapsulate any BUM traffic from attached VMs in an IP multicast
packet, whose destination address is the associated multicast group
address, and transmit the packet to the data center fabric. Thus,
PIM must be running in the fabric to maintain a multicast
distribution tree per VNI.
Alternatively, rather than setting up a multicast distribution tree
per VNI, a tree can be set up whenever hosts within the VNI wish to
exchange multicast traffic. For example, whenever a VTEP receives an
IGMP report from a locally connected host, it would translate this
into a PIM join message which will be propagated into the IP fabric.
In order to ensure this join message is sent to the IP fabric rather
than over the VXLAN interface (since the VTEP will have a route back
to the source of the multicast packet over the VXLAN interface and so
would naturally attempt to send the join over this interface) a more
specific route back to the source over the IP fabric must be
configured. In this approach PIM must be configured on the SVIs
associated with the VXLAN interface.
Another use case of PIM and IGMP in data centers is when IPTV servers
use multicast to deliver content from the data center to end users.
IPTV is typically a one to many application where the hosts are
configured for IGMPv3, the switches are configured with IGMP
snooping, and the routers are running PIM-SSM mode. Often redundant
servers send multicast streams into the network and the network is
forwards the data across diverse paths.
Windows Media servers send multicast streams to clients. Windows
Media Services streams to an IP multicast address and all clients
subscribe to the IP address to receive the same stream. This allows
a single stream to be played simultaneously by multiple clients and
thus reducing bandwidth utilization.
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3.4. Advantages and disadvantages
Arguably the biggest advantage of using PIM and IGMP to support one-
to-many communication in data centers is that these protocols are
relatively mature. Consequently, PIM is available in most routers
and IGMP is supported by most hosts and routers. As such, no
specialized hardware or relatively immature software is involved in
using them in data centers. Furthermore, the maturity of these
protocols means their behaviour and performance in operational
networks is well-understood, with widely available best-practices and
deployment guides for optimizing their performance.
However, somewhat ironically, the relative disadvantages of PIM and
IGMP usage in data centers also stem mostly from their maturity.
Specifically, these protocols were standardized and implemented long
before the highly-virtualized multi-tenant data centers of today
existed. Consequently, PIM and IGMP are neither optimally placed to
deal with the requirements of one-to-many communication in modern
data centers nor to exploit characteristics and idiosyncrasies of
data centers. For example, there may be thousands of VMs
participating in a multicast session, with some of these VMs
migrating to servers within the data center, new VMs being
continually spun up and wishing to join the sessions while all the
time other VMs are leaving. In such a scenario, the churn in the PIM
and IGMP state machines, the volume of control messages they would
generate and the amount of state they would necessitate within
routers, especially if they were deployed naively, would be
untenable.
4. Alternative options for handling one-to-many traffic
Section 2 has shown that there is likely to be an increasing amount
one-to-many communications in data centers. And Section 3 has
discussed how conventional multicast may be used to handle this
traffic. Having said that, there are a number of alternative options
of handling this traffic pattern in data centers, as discussed in the
subsequent section. It should be noted that many of these techniques
are not mutually-exclusive; in fact many deployments involve a
combination of more than one of these techniques. Furthermore, as
will be shown, introducing a centralized controller or a distributed
control plane, makes these techniques more potent.
4.1. Minimizing traffic volumes
If handling one-to-many traffic in data centers can be challenging
then arguably the most intuitive solution is to aim to minimize the
volume of such traffic.
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It was previously mentioned in Section 2 that the three main causes
of one-to-many traffic in data centers are applications, overlays and
protocols. While, relatively speaking, little can be done about the
volume of one-to-many traffic generated by applications, there is
more scope for attempting to reduce the volume of such traffic
generated by overlays and protocols. (And often by protocols within
overlays.) This reduction is possible by exploiting certain
characteristics of data center networks: fixed and regular topology,
owned and exclusively controlled by single organization, well-known
overlay encapsulation endpoints etc.
A way of minimizing the amount of one-to-many traffic that traverses
the data center fabric is to use a centralized controller. For
example, whenever a new VM is instantiated, the hypervisor or
encapsulation endpoint can notify a centralized controller of this
new MAC address, the associated virtual network, IP address etc. The
controller could subsequently distribute this information to every
encapsulation endpoint. Consequently, when any endpoint receives an
ARP request from a locally attached VM, it could simply consult its
local copy of the information distributed by the controller and
reply. Thus, the ARP request is suppressed and does not result in
one-to-many traffic traversing the data center IP fabric.
Alternatively, the functionality supported by the controller can
realized by a distributed control plane. BGP-EVPN [RFC7432, RFC8365]
is the most popular control plane used in data centers. Typically,
the encapsulation endpoints will exchange pertinent information with
each other by all peering with a BGP route reflector (RR). Thus,
information about local MAC addresses, MAC to IP address mapping,
virtual networks identifiers etc can be disseminated. Consequently,
ARP requests from local VMs can be suppressed by the encapsulation
endpoint.
4.2. Head end replication
A popular option for handling one-to-many traffic patterns in data
centers is head end replication (HER). HER means the traffic is
duplicated and sent to each end point individually using conventional
IP unicast. Obvious disadvantages of HER include traffic duplication
and the additional processing burden on the head end. Nevertheless,
HER is especially attractive when overlays are in use as the
replication can be carried out by the hypervisor or encapsulation end
point. Consequently, the VMs and IP fabric are unmodified and
unaware of how the traffic is delivered to the multiple end points.
Additionally, it is possible to use a number of approaches for
constructing and disseminating the list of which endpoints should
receive what traffic and so on.
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For example, the reluctance of data center operators to enable PIM
and IGMP within the data center fabric means VXLAN is often used with
HER. Thus, BUM traffic from each VNI is replicated and sent using
unicast to remote VTEPs with VMs in that VNI. The list of remote
VTEPs to which the traffic should be sent may be configured manually
on the VTEP. Alternatively, the VTEPs may transmit appropriate state
to a centralized controller which in turn sends each VTEP the list of
remote VTEPs for each VNI. Lastly, HER also works well when a
distributed control plane is used instead of the centralized
controller. Again, BGP-EVPN may be used to distribute the
information needed to faciliate HER to the VTEPs.
4.3. BIER
As discussed in Section 3.4, PIM and IGMP face potential scalability
challenges when deployed in data centers. These challenges are
typically due to the requirement to build and maintain a distribution
tree and the requirement to hold per-flow state in routers. Bit
Index Explicit Replication (BIER) [RFC 8279] is a new multicast
forwarding paradigm that avoids these two requirements.
When a multicast packet enters a BIER domain, the ingress router,
known as the Bit-Forwarding Ingress Router (BFIR), adds a BIER header
to the packet. This header contains a bit string in which each bit
maps to an egress router, known as Bit-Forwarding Egress Router
(BFER). If a bit is set, then the packet should be forwarded to the
associated BFER. The routers within the BIER domain, Bit-Forwarding
Routers (BFRs), use the BIER header in the packet and information in
the Bit Index Forwarding Table (BIFT) to carry out simple bit- wise
operations to determine how the packet should be replicated optimally
so it reaches all the appropriate BFERs.
BIER is deemed to be attractive for facilitating one-to-many
communications in data ceneters [I-D.ietf-bier-use-cases]. The
deployment envisioned with overlay networks is that the the
encapsulation endpoints would be the BFIR. So knowledge about the
actual multicast groups does not reside in the data center fabric,
improving the scalability compared to conventional IP multicast.
Additionally, a centralized controller or a BGP-EVPN control plane
may be used with BIER to ensure the BFIR have the required
information. A challenge associated with using BIER is that, unlike
most of the other approaches discussed in this draft, it requires
changes to the forwarding behaviour of the routers used in the data
center IP fabric.
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4.4. Segment Routing
Segment Routing (SR) [I-D.ietf-spring-segment-routing] adopts the the
source routing paradigm in which the manner in which a packet
traverses a network is determined by an ordered list of instructions.
These instructions are known as segments may have a local semantic to
an SR node or global within an SR domain. SR allows enforcing a flow
through any topological path while maintaining per-flow state only at
the ingress node to the SR domain. Segment Routing can be applied to
the MPLS and IPv6 data-planes. In the former, the list of segments
is represented by the label stack and in the latter it is represented
as a routing extension header. Use-cases are described in [I-D.ietf-
spring-segment-routing] and are being considered in the context of
BGP-based large-scale data-center (DC) design [RFC7938].
Multicast in SR continues to be discussed in a variety of drafts and
working groups. The SPRING WG has not yet been chartered to work on
Multicast in SR. Multicast can include locally allocating a Segment
Identifier (SID) to existing replication solutions, such as PIM,
mLDP, P2MP RSVP-TE and BIER. It may also be that a new way to signal
and install trees in SR is developed without creating state in the
network.
5. Conclusions
As the volume and importance of one-to-many traffic in data centers
increases, conventional IP multicast is likely to become increasingly
unattractive for deployment in data centers for a number of reasons,
mostly pertaining its inherent relatively poor scalability and
inability to exploit characteristics of data center network
architectures. Hence, even though IGMP/MLD is likely to remain the
most popular manner in which end hosts signal interest in joining a
multicast group, it is unlikely that this multicast traffic will be
transported over the data center IP fabric using a multicast
distribution tree built by PIM. Rather, approaches which exploit
characteristics of data center network architectures (e.g. fixed and
regular topology, owned and exclusively controlled by single
organization, well-known overlay encapsulation endpoints etc.) are
better placed to deliver one-to-many traffic in data centers,
especially when judiciously combined with a centralized controller
and/or a distributed control plane (particularly one based on BGP-
EVPN).
6. IANA Considerations
This memo includes no request to IANA.
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Internet-Draft Multicast in the Data Center June 2018
7. Security Considerations
No new security considerations result from this document
8. Acknowledgements
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
9.2. Informative References
[I-D.ietf-bier-use-cases]
Kumar, N., Asati, R., Chen, M., Xu, X., Dolganow, A.,
Przygienda, T., Gulko, A., Robinson, D., Arya, V., and C.
Bestler, "BIER Use Cases", draft-ietf-bier-use-cases-06
(work in progress), January 2018.
[I-D.ietf-nvo3-geneve]
Gross, J., Ganga, I., and T. Sridhar, "Geneve: Generic
Network Virtualization Encapsulation", draft-ietf-
nvo3-geneve-06 (work in progress), March 2018.
[I-D.ietf-nvo3-vxlan-gpe]
Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
Extension for VXLAN", draft-ietf-nvo3-vxlan-gpe-06 (work
in progress), April 2018.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
<https://www.rfc-editor.org/info/rfc2236>.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
DOI 10.17487/RFC2710, October 1999,
<https://www.rfc-editor.org/info/rfc2710>.
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Internet-Draft Multicast in the Data Center June 2018
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601,
DOI 10.17487/RFC4601, August 2006,
<https://www.rfc-editor.org/info/rfc4601>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
<https://www.rfc-editor.org/info/rfc5015>.
[RFC6820] Narten, T., Karir, M., and I. Foo, "Address Resolution
Problems in Large Data Center Networks", RFC 6820,
DOI 10.17487/RFC6820, January 2013,
<https://www.rfc-editor.org/info/rfc6820>.
[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, DOI 10.17487/RFC7348, August 2014,
<https://www.rfc-editor.org/info/rfc7348>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7637] Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network
Virtualization Using Generic Routing Encapsulation",
RFC 7637, DOI 10.17487/RFC7637, September 2015,
<https://www.rfc-editor.org/info/rfc7637>.
[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
BGP for Routing in Large-Scale Data Centers", RFC 7938,
DOI 10.17487/RFC7938, August 2016,
<https://www.rfc-editor.org/info/rfc7938>.
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[RFC8014] Black, D., Hudson, J., Kreeger, L., Lasserre, M., and T.
Narten, "An Architecture for Data-Center Network
Virtualization over Layer 3 (NVO3)", RFC 8014,
DOI 10.17487/RFC8014, December 2016,
<https://www.rfc-editor.org/info/rfc8014>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
Authors' Addresses
Mike McBride
Huawei
Email: michael.mcbride@huawei.com
Olufemi Komolafe
Arista Networks
Email: femi@arista.com
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