Hi Russ,
Thanks again for your review and sorry for having missed this email. I’ve adopted your suggestions and incorporated them into version -08. (attached).
Network Working Group A. Karan
Internet-Draft C. Filsfils
Intended status: Informational IJ. Wijnands, Ed.
Expires: November 19, 2015 Cisco Systems, Inc.
B. Decraene
Orange
May 18, 2015
Multicast only Fast Re-Route
draft-ietf-rtgwg-mofrr-08
Abstract
As IPTV deployments grow in number and size, service providers are
looking for solutions that minimize the service disruption due to
faults in the IP network carrying the packets for these services.
This document describes a mechanism for minimizing packet loss in a
network when node or link failures occur. Multicast only Fast Re-
Route (MoFRR) works by making simple enhancements to multicast
routing protocols such as PIM and mLDP.
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 http://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 November 19, 2015.
Copyright Notice
Copyright (c) 2015 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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. Conventions used in this document . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . 4
3. Determination of the secondary UMH . . . . . . . . . . . . . 4
3.1. ECMP-mode MoFRR . . . . . . . . . . . . . . . . . . . . . 4
3.2. Non-ECMP-mode MoFRR . . . . . . . . . . . . . . . . . . . 5
4. Upstream Multicast Hop Selection . . . . . . . . . . . . . . 5
4.1. PIM . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. mLDP . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Detecting Failures . . . . . . . . . . . . . . . . . . . . . 6
6. MoFRR applicability to Dual-Plane Topology . . . . . . . . . 7
7. Other Topologies . . . . . . . . . . . . . . . . . . . . . . 10
8. Capacity Planning for MoFRR . . . . . . . . . . . . . . . . . 11
9. PE nodes . . . . . . . . . . . . . . . . . . . . . . . . . . 11
10. Other Applications . . . . . . . . . . . . . . . . . . . . . 11
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
12. Security Considerations . . . . . . . . . . . . . . . . . . . 12
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
14. Contributor Addresses . . . . . . . . . . . . . . . . . . . . 12
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
15.1. Normative References . . . . . . . . . . . . . . . . . . 13
15.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Different solutions have been developed and deployed to improve
service guarantees, both for multicast video traffic and Video on
Demand traffic. Most of these solutions are geared towards finding
an alternate path around one or more failed network elements (link,
node, path failures).
This document describes a mechanism for minimizing packet loss in a
network when node or link failures occur. Multicast only Fast Re-
Route (MoFRR) works by making simple changes to the way selected
routers use multicast protocols such as PIM and mLDP. No changes to
the protocols themselves are required. With MoFRR, in many cases,
multicast routing protocols don't necessarily have to depend on or
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have to wait on unicast routing protocols to detect network failures,
see Section 5.
On a Merge Point MoFRR logic determines a primary Upstream Multicast
Hop (UMH) and a secondary UMH and joins the tree via both
simultaneously. Data packets are received over the primary and
secondary paths. Only the packets from the primary UMH are accepted
and forwarded down the tree, the packets from the secondary UMH are
discarded. The UMH determination is different for PIM and mLDP and
explained in Section 4. When a failure is detected on the path to
the primary UMH, the repair occurs by changing the secondary UMH into
the primary and the primary into the secondary. Since the repair is
local, it is fast - greatly improving convergence times in the event
of node or link failures on the path to the primary UMH.
1.1. Conventions used in this document
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 [RFC2119].
1.2. Terminology
MoFRR: Multicast only Fast Re-Route.
ECMP: Equal Cost Multi-Path.
mLDP: Multi-point Label Distribution Protocol.
PIM: Protocol Independent Multicast.
UMH: Upstream Multicast Hop, a candidate next-hop that can be used
to reach the root of the tree.
tree: Either a PIM (S,G)/(*,G) tree or a mLDP P2MP or MP2MP LSP.
OIF: Outgoing InterFace, an interface used to forward multicast
packets down the tree towards the receivers. Either a PIM
(S,G)/(*,G) tree or a mLDP P2MP or MP2MP LSP.
LFA: Loop Free Alternate as defined in [RFC5286]. In unicast Fast
ReRoute, this is an alternate next-hop which can be used to reach
a unicast destination without using the protected link or node.
Merge Point: A router that joins a multicast stream via two
divergent upstream paths.
RPF: Reverse Path Forwarding.
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RP: Rendezvous Point.
LSR: Label Switched Router.
BFD: Bidirectional Forwarding Detection.
IGP: Interior Gateway Protocol.
MVPN: Multicast Virtual Private Networks.
POP: Point Of Presence, an access point into the network
2. Basic Overview
The basic idea of MoFRR is for a Merge Point router to join a
multicast tree via two divergent upstream paths in order to get
maximum redundancy. The determination of this alternate upstream is
defined in Section 3.
In order to maximize robustness against any failure, the two paths
should be as diverse as possible. Ideally, they should not merge
upstream. Sometimes the topology guarantees maximal redundancy,
other times additional configuration or techniques are needed to
enforce it. See Section 6 for more discussion on the applicability
of MoFRR depending on the network topology.
A Merge Point router should only accept and forward on one of the
upstream paths at a time in order to avoid duplicate packet
forwarding. The selection of the primary and secondary UMH is done
by the MoFRR logic and normally based on unicast routing to find loop
free candidates. This is described in Section 4.
Note, the impact of additional amount of data on the network is
mitigated when tree membership is densely populated. When a part of
the network has redundant data flowing, join latency for new joining
members is reduced because its likely a tree Merge Point is not far
away.
3. Determination of the secondary UMH
The secondary UMH is a Loop Free Alternate (LFA) as per [RFC5286].
3.1. ECMP-mode MoFRR
If the IGP installs two ECMP paths to the source, then as per
[RFC5286] the LFA is a primary Next-hop. If the Multicast tree is
enabled for ECMP-Mode MoFRR, the router installs them as primary and
secondary UMH. Before the failure, only packets received from the
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primary UMH path are processed while packets received from the
secondary UMH are dropped.
The selected primary UMH SHOULD be the same as if the MoFRR extension
was not enabled.
If more than two ECMP paths exist, one is selected as primary and
another as secondary UMH. The selection of the primary and secondary
is a local decision. Information from the IGP link-state topology
could be leveraged to optimize this selection such that the primary
and secondary path are maximal divergent and don't lead to the same
upstream node. Note that MoFRR does not restrict the number of UMH
paths that are joined. Implementations may use as many paths as are
configured.
3.2. Non-ECMP-mode MoFRR
A router X configured for non-ECMP-mode MoFRR for a Multicast tree
joins a primary path to its primary UMH and a secondary path to its
LFA UMH. In order to prevent control-plane loops a router MUST stop
joining the secondary UMH if this UMH is the only member in the OIF
list.
To illustrate the reason for this rule, let's consider the example in
FIG3. If PE1 and PE2 have received an IGMP request for a Multicast
tree, they will both join the primary path on their plane and a
secondary path to the neighbor PE. If their receivers would leave at
the same time, it could be possible for the Multicast tree on PE1 and
PE2 to never get deleted as each PE refresh each other via the
secondary path joins (remember that a secondary path join is not
distinguishable from a primary join).
4. Upstream Multicast Hop Selection
An Upstream Multicast Hop (UMH) is a candidate next-hop that can be
used to reach the root of the tree. This is normally based on
unicast routing to find loop free candidate(s). With MoFRR
procedures we select a primary and a backup UMH. The procedures for
determining the UMH are different for PIM and mLDP.
4.1. PIM
The UMH selection in PIM is also known as the Reverse Path Forwarding
(RPF) procedure. Based on a unicast route lookup on either the
Source address or Rendezvous Point (RP) [RFC4601], an upstream
interface is selected for sending the PIM Joins/Prunes AND accepting
the multicast packets. The interface the packets are received on is
used to pass or fail the RPF check. If packets are received on an
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interface that was not selected by the RPF procedure, or not the
primary, the packets are discarded.
4.2. mLDP
The UMH selection in mLDP also depends on unicast routing, but the
difference with PIM is that the acceptance of multicast packets is
based on MPLS labels and independent of the interface the packet is
received on. Using the procedures as defined in [RFC6388] an
upstream Label Switched Router (LSR) is elected. The upstream LSR
that was elected for a Label Switched Path (LSP) gets a unique local
MPLS Label allocated. Multicast packets are only forwarded if the
MPLS label matches the MPLS label that was allocated for that LSPs
(primary) upstream LSR.
5. Detecting Failures
Once the two paths are established, the next step is detecting a
failure on the primary path to know when to switch to the backup
path. This is a local issue but this section explores some
possibilities.
The first (and simplest) option is to detect the failure of the local
interface as it it's done for unicast Fast ReRoute. Detection can be
performed using the loss of signal or the loss of probing packets
(e.g. BFD). This option can be used in combination with the other
options as documented below. Just like for unicast fast reroute,
50msec switch-over is possible.
A second option consists of comparing the packets received on the
primary and secondary streams but only forwarding one of them -- the
first one received, no matter which interface it is received on.
Zero packet loss is possible for RTP-based streams.
A third option assumes a minimum known packet rate for a given data
stream. If a packet is not received on the primary RPF within this
time frame, the router assumes primary path failure and switches to
the secondary RPF interface. 50msec switch-over may be possible for
high rate stream (e.g. IP TV where SD video has a continuous inter-
packet gap of ~ 3msec) but in general the delay is dependant on the
rate of the multicast stream.
A fourth option leverages the significant improvements of the IGP
convergence speed. When the primary path to the source is withdrawn
by the IGP, the MoFRR-enabled router switches over to the backup
path, the UMH is changed to the secondary UMH. Since the secondary
path is already in place, and assuming it is disjoint from the
primary path, convergence times would not include the time required
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to build a new tree and hence are smaller. Sub-second to sub-200msec
switch-over should be possible.
6. MoFRR applicability to Dual-Plane Topology
MoFRR applicability is topology dependent. The applicability is the
same as LFA FRR which is discussed in [RFC6571].
The following section will discuss MoFRR applicability to dual-plane
network topologies.
MoFRR works best in dual-planes topologies as illustrated in the
figures below. MoFRR may be enabled on any router in the network.
In the figures below, MoFRR is shown enabled on the Provider Edge
(PE) routers to illustrate one way in which the technology may be
deployed.
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S
P / \ P
/ \
^ G1 R1 ^
P / \ P
/ \
G2----------R2 ^
| \ | \ P
^ | \ | \
P | G3----------R3
| | | |
| | | | ^
G4---|------R4 | P
^ \ | \ |
P \ | \ |
G5----------R5
^ | | ^
P | | P
| |
Gi Ri
\ \__ ^ /|
\ \ S1/ | ^
^ \ ^\ / |P2
P1 \ S2\_/__ |
\ / \|
PE1 PE2
P = Primary path
S = Secondary path
FIG1. Two-Plane Network Design
The topology has two planes, a primary plane and a secondary plane
that are fully disjoint from each other all the way into the POPs.
This two plane design is common in service provider networks as it
eliminates single point of failures in their core network. The links
marked P indicate the normal (Primary) path of how the PIM joins flow
from the POPs towards the source of the network. Multicast streams,
especially for the densely watched channels, typically flow along
both the planes in the network anyway.
The only change MoFRR adds to this is on the links marked S where the
PE routers join a secondary path to their secondary ECMP UMH. As a
result of this, each PE router receives two copies of the same
stream, one from the primary plane and the other from the secondary
plane. As a result of normal UMH behavior, the multicast stream
received over the primary path is accepted and forwarded to the
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downstream receivers. The copy of the stream received from the
secondary UNH is discarded.
When a router detects a routing failure on the path to its primary
UMH, it will switch to the secondary UMH and accept packets for that
stream. If the failure is repaired the router may switch back. The
primary and secondary UMHs have only local context and not end-to-end
context.
As one can see, MoFRR achieves the faster convergence by pre-building
the secondary multicast tree and receiving the traffic on that
secondary path. The example discussed above is a simple case where
there are two ECMP paths from each PE device towards the source, one
along the primary plane and one along the secondary. In cases where
the topology is asymmetric or is a ring, this ECMP nature does not
hold, and additional rules have to be taken into account to choose
when and where to join the secondary path.
MoFRR is appealing in such topologies for the following reasons:
1. Ease of deployment and simplicity: the functionality is only
required on the PE devices although it may be configured on all
routers in the topology. Furthermore, each PE device can be
enabled separately, there is no need for a network wide
coordination in order to deploy MoFRR. Inter-operability testing
is not required as there are no PIM or mLDP protocol change.
2. End-to-end failure detection and recovery: any failure along the
path from the source to the PE can be detected and repaired with
the secondary disjoint stream.(see Section 5 options 2, 3, 4)
3. Capacity Efficiency: as illustrated in the previous example, the
Multicast trees corresponding to IPTV channels cover the backbone
and distribution topology in a very dense manner. As a
consequence, the secondary path graft into the normal Multicast
trees (ie. trees signaled by PIM or mLDP without MoFRR extension)
at the aggregation level and hence do not demand any extra
capacity either on the distribution links or in the backbone.
They simply use the capacity that is normally used, without any
duplication. This is different from conventional FRR mechanisms
which often duplicate the capacity requirements when the backup
path crosses links/nodes which already carry the primary/normal
tree and hence twice as much capacity is required.
4. Loop free: the secondary path join is sent on an ECMP disjoint
path. By definition, the neighbor receiving this request is
closer to the source and hence will not cause a loop.
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The topology we just analyzed is very frequent and can be modelled as
per FIG2. The PE has two ECMP disjoint paths to the source. Each
ECMP path uses a disjoint plane of the network.
Source
/ \
Plane1 Plane2
| |
A1 A2
\ /
PE
FIG2. PE is dual-homed to Dual-Plane Backbone
Another frequent topology is described in FIG3. PEs are grouped by
pairs. In each pair, each PE is connected to a different plane.
Each PE has one single shortest-path to a source (via its connected
plane). There is no ECMP like in FIG2. However, there is clearly a
way to provide MoFRR benefits as each PE can offer a disjoint
secondary path to the other plane PE (via the disjoint path).
MoFRR secondary neighbor selection process needs to be extended in
this case as one cannot simply rely on using an ECMP path as
secondary neighbor. This extension is referred to as non-ecmp
extension and is described in Section 3.2.
Source
/ \
Plane1 Plane2
| |
A1 A2
| |
PE1----PE2
FIG3. PEs are connected in pairs to Dual-Plane Backbone
7. Other Topologies
As mentioned in section Section 6, MoFRR works best in dual-plane
topologies. If MoFRR is applied to none dual-plane networks, its
possible that the secondary path is effected by the same failure that
effected the primary path. In that case, there is no guarentee that
the backup path will provide an un-interupted traffic flow of packets
without loss or duplication.
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8. Capacity Planning for MoFRR
The previous section has described two very frequent designs (FIG2
and FIG3) which provide maximum MoFRR benefits.
Designers with topologies different than FIG2 and FIG3 can still
benefit from MoFRR thanks to the use of capacity planning tools.
Such tools are able to simulate the ability of each PE to build two
disjoint branches of the same tree. This for hundreds of PEs and
hundreds of sources.
This allows to assess the MoFRR protection coverage of a given
network, for a set of sources.
If the protection coverage is deemed insufficient, the designer can
use such tool to optimize the topology (add links, change IGP
metrics).
9. PE nodes
Many Service Providers devise their topology such that PEs have
disjoint paths to the multicast sources. MoFRR leverages the
existence of these disjoint paths without any PIM or mLDP protocol
modification. Interoperability testing is thus not required. In
such topologies, MoFRR only needs to be deployed on the PE devices.
Each PE device can be enabled one by one.
10. Other Applications
While all the examples in this document show the MoFRR applicability
on PE devices, it is clear that MoFRR could be enabled on aggregation
or core routers.
MoFRR can be popular in Data Center network configurations. With the
advent of lower cost ethernet and increasing port density in routers,
there is more meshed connectivity than ever before. When using a
3-level access, distribution, and core layers in a Data Center, there
is a lot of inexpensive bandwidth connecting the layers. This will
lend itself to more opportunities for ECMP paths at multiple layers.
This allows for multiple layers of redundancy protecting link and
node failure at each layer with minimal redundancy cost.
Redundancy costs are reduced because only one packet is forwarded at
every link along the primary and secondary data paths so there is no
duplication of data on any link thereby providing make-before-break
protection at a very small cost.
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A MoFRR router only accepts packets from the primary path and
discards packets from the secondary path. For that reason,
management applications (like ping and mtrace) will not work when
verifying the secondary path.
The MoFRR principle may be applied to MVPNs.
11. IANA Considerations
This document makes no request of IANA.
12. Security Considerations
There are no security considerations for this design other than what
is already in the main PIM specification [RFC4601] and mLDP
specification [RFC6388].
13. Acknowledgments
Thanks to Dave Oran and Alvaro Retana for their review and comments
on this document.
The authors would like to especially acknowledge the contribution
from Dino Farinacci, John Zwiebel and Greg Shepherd for the genesis
of the MoFRR concept.
14. Contributor Addresses
Below is a list of other contributing authors in alphabetical order:
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Dino Farinacci
Email: farinacci@xxxxxxxxx
Wim Henderickx
Alcatel-Lucent
Copernicuslaan 50
Antwerp 2018
Belgium
Email: wim.henderickx@xxxxxxxxxxxxxxxxxx
Uwe Joorde
Deutsche Telekom
Dahlweg 100
D-48153 Muenster
Germany
Email: Uwe.Joorde@xxxxxxxxxx
Nicolai Leymann
Deutsche Telekom
Winterfeldtstrasse 21
Berlin 10781
DE
Email: N.Leymann@xxxxxxxxxx
Jeff Tantsura
Ericsson
300 Holger Way
San Jose CA 95134
USA
Email: jeff.tantsura@xxxxxxxxxxxx
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
15.2. 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.
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[RFC6388] Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
"Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, November 2011.
[RFC6571] Filsfils, C., Francois, P., Shand, M., Decraene, B.,
Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free
Alternate (LFA) Applicability in Service Provider (SP)
Networks", RFC 6571, June 2012.
Authors' Addresses
Apoorva Karan
Cisco Systems, Inc.
3750 Cisco Way
San Jose CA, 95134
USA
Email: apoorva@xxxxxxxxx
Clarence Filsfils
Cisco Systems, Inc.
De kleetlaan 6a
Diegem BRABANT 1831
Belgium
Email: cfilsfil@xxxxxxxxx
IJsbrand Wijnands (editor)
Cisco Systems, Inc.
De Kleetlaan 6a
Diegem 1831
BE
Email: ice@xxxxxxxxx
Bruno Decraene
Orange
38-40 rue du General Leclerc
Issy Moulineaux Cedex 9, 92794
FR
Email: bruno.decraene@xxxxxxxxxx
Karan, et al. Expires November 19, 2015 [Page 14]
Thx,
Ice.
> On 14 May 2015, at 00:39, Jari Arkko <jari.arkko@xxxxxxxxx> wrote:
>
> Thanks for your review, Russ.
>
> For what it is worth, I do not see any changes relating to your comments in the -07. Have you authors seen Russ’ comments?
>
> Jari
>
> On 17 Apr 2015, at 18:25, Russ Housley <housley@xxxxxxxxxxxx> wrote:
>
>> I am the assigned Gen-ART reviewer for this draft. For background on
>> Gen-ART, please see the FAQ at
>> <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.
>>
>> This review is in response to a request for early Gen-ART review.
>>
>> Document: draft-ietf-rtgwg-mofrr-06
>> Reviewer: Russ Housley
>> Review Date: 2015-04-17
>> IETF LC End Date: 2015-04-30
>> IESG Telechat date: unknown
>>
>> Summary: Almost Ready
>>
>>
>> Major Concerns:
>>
>> None
>>
>>
>> Minor Concerns:
>>
>> Please add POP to the list of terms in Section 1.2.
>>
>> The introduction to Section 6 really only talks about Section 6.1.
>> Perhaps Sections 6 and 6.1 should be merged. If they are merged, it
>> could look like this:
>>
>> 6. MoFRR Applicability to Dual-Plane Topology
>>
>> MoFRR applicability is topology dependent. The applicability is the
>> same as LFA FRR which is discussed in [RFC6571].
>>
>> MoFRR works best in dual-planes topologies as illustrated in the
>> figures below. MoFRR may be enabled on any router in the network.
>> In the figures below, MoFRR is shown enabled on the Provider Edge
>> (PE) routers to illustrate one way in which the technology may be
>> deployed.
>>
>> . . .
>>
>> If this suggestion is taken, Sections 6.2, 6.3, and 6.4 could become
>> top-level sections of their own.
>>
>>
>> Other Comments:
>>
>> The figures are referenced in many ways: FIG3, Fig3, and Fig 3.
>> Please pick one style and use it throughout the document.
>>
>> Section 1, 2nd paragraph: add a period at the end of the paragraph.
>>
>> Section 1.2, LFA definition: add a period after the first sentence.
>>
>> Section 4, intro paragraph: Delete " See below;" from the end.
>>
>> Section 5, 1st paragraph: s/section explore some/section explores some/
>>
>