draft-ietf-rtgwg-mofrr-03.txt   draft-ietf-rtgwg-mofrr-04.txt 
Network Working Group A. Karan Network Working Group A. Karan
Internet-Draft C. Filsfils Internet-Draft C. Filsfils
Intended status: Informational D. Farinacci Intended status: Informational Cisco Systems, Inc.
Expires: July 21, 2014 IJ. Wijnands, Ed. Expires: November 15, 2014 D. Farinacci
lispers.net
IJ. Wijnands, Ed.
Cisco Systems, Inc. Cisco Systems, Inc.
B. Decraene B. Decraene
France Telecom Orange
U. Joorde U. Joorde
Deutsche Telekom Deutsche Telekom
W. Henderickx W. Henderickx
Alcatel-Lucent Alcatel-Lucent
January 17, 2014 May 14, 2014
Multicast only Fast Re-Route Multicast only Fast Re-Route
draft-ietf-rtgwg-mofrr-03 draft-ietf-rtgwg-mofrr-04
Abstract Abstract
As IPTV deployments grow in number and size, service providers are As IPTV deployments grow in number and size, service providers are
looking for solutions that minimize the service disruption due to looking for solutions that minimize the service disruption due to
faults in the IP network carrying the packets for these services. faults in the IP network carrying the packets for these services.
This draft describes a mechanism for minimizing packet loss in a This draft describes a mechanism for minimizing packet loss in a
network when node or link failures occur. Multicast only Fast Re- network when node or link failures occur. Multicast only Fast Re-
Route (MoFRR) works by making simple enhancements to multicast Route (MoFRR) works by making simple enhancements to multicast
routing protocols such as PIM and mLDP. routing protocols such as PIM and mLDP.
Status of this Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 21, 2014. This Internet-Draft will expire on November 15, 2014.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . 4
3. Upstream Multicast Hop Selection . . . . . . . . . . . . . . . 4 3. Determination of the secondary UMH . . . . . . . . . . . . . 5
3.1. PIM . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. ECMP-mode MoFRR . . . . . . . . . . . . . . . . . . . . . 5
3.2. mLDP . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Non-ECMP-mode MoFRR . . . . . . . . . . . . . . . . . . . 5
4. Topologies for MoFRR . . . . . . . . . . . . . . . . . . . . . 5 4. Upstream Multicast Hop Selection . . . . . . . . . . . . . . 5
4.1. Dual-Plane Topology . . . . . . . . . . . . . . . . . . . 5 4.1. PIM . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Detecting Failures . . . . . . . . . . . . . . . . . . . . . . 8 4.2. mLDP . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. ECMP-mode MoFRR . . . . . . . . . . . . . . . . . . . . . . . 9 5. Detecting Failures . . . . . . . . . . . . . . . . . . . . . 6
7. Non-ECMP-mode MoFRR . . . . . . . . . . . . . . . . . . . . . 9 6. MoFRR applicability . . . . . . . . . . . . . . . . . . . . . 7
8. Keep It Simple Principle . . . . . . . . . . . . . . . . . . . 10 6.1. Dual-Plane Topology . . . . . . . . . . . . . . . . . . . 7
9. Capacity Planning for MoFRR . . . . . . . . . . . . . . . . . 11 6.2. Capacity Planning for MoFRR . . . . . . . . . . . . . . . 10
10. Other Applications . . . . . . . . . . . . . . . . . . . . . . 11 6.3. PE nodes . . . . . . . . . . . . . . . . . . . . . . . . 11
11. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6.4. Other Applications . . . . . . . . . . . . . . . . . . . 11
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
13. Contributor Addresses . . . . . . . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
14.1. Normative References . . . . . . . . . . . . . . . . . . . 12 10. Contributor Addresses . . . . . . . . . . . . . . . . . . . . 12
14.2. Informative References . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
Multiple techniques have been developed and deployed to improve Different solutions have been developed and deployed to improve
service guarantees, both for multicast video traffic and Video on service guarantees, both for multicast video traffic and Video on
Demand traffic. Most existing solutions are geared towards finding Demand traffic. Most of these solutions are geared towards finding
an alternate path around one or more failed network elements (link, an alternate path around one or more failed network elements (link,
node, path failures). node, path failures).
This draft describes a mechanism for minimizing packet loss in a This draft describes a mechanism for minimizing packet loss in a
network when node or link failures occur. Multicast only Fast Re- network when node or link failures occur. Multicast only Fast Re-
Route (MoFRR) works by making simple changes to the way selected Route (MoFRR) works by making simple changes to the way selected
routers use multicast protocols such as PIM and mLDP. No changes to routers use multicast protocols such as PIM and mLDP. No changes to
the protocols themselves are required. With MoFRR, in many cases, the protocols themselves are required. With MoFRR, in many cases,
multicast routing protocols don't necessarily have to depend on or multicast routing protocols don't necessarily have to depend on or
have to wait on unicast routing protocols to detect network failures. 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 On a Merge Point MoFRR logic determines a primary Upstream Multicast
Hop (UMH) and a secondary UMH and joins the tree via both Hop (UMH) and a secondary UMH and joins the tree via both
simultaneously. Data packets are received over the primary and simultaneously. Data packets are received over the primary and
secondary paths. Only the packets from the primary UMH are accepted secondary paths. Only the packets from the primary UMH are accepted
and forwarded down the tree, the packets from the secondary UMH are and forwarded down the tree, the packets from the secondary UMH are
discarded. The UMH determination is different for PIM and mLDP and discarded. The UMH determination is different for PIM and mLDP and
explained later in this document. When a failure is detected on the explained in Section 4. When a failure is detected on the path to
path to the primary UMH, the repair occurs by changing the secondary the primary UMH, the repair occurs by changing the secondary UMH into
UMH into the primary and the primary into the secondary. Since the the primary and the primary into the secondary. Since the repair is
repair is local, it is fast - greatly improving convergence times in local, it is fast - greatly improving convergence times in the event
the event of node or link failures on the path to the primary UMH. of node or link failures on the path to the primary UMH.
1.1. Conventions used in this document 1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Terminology 1.2. Terminology
MoFRR : Multicast only Fast Re-Route. MoFRR: Multicast only Fast Re-Route.
ECMP : Equal Cost Multi-Path. ECMP: Equal Cost Multi-Path.
mLDP : Multi-point Label Distribution Protocol. mLDP: Multi-point Label Distribution Protocol.
PIM : Protocol Independent Multicast. PIM: Protocol Independent Multicast.
UMH : Upstream Multicast Hop, a candidate next-hop that can be used UMH: Upstream Multicast Hop, a candidate next-hop that can be used
to reach the root of the tree. to reach the root of the tree.
tree : Either a PIM (S,G)/(*,G) tree or a mLDP P2MP or MP2MP LSP. tree: Either a PIM (S,G)/(*,G) tree or a mLDP P2MP or MP2MP LSP.
OIF : Outgoing InterFace, an interface used to forward multicast OIF: Outgoing InterFace, an interface used to forward multicast
packets down the tree towards the receivers. Either a PIM packets down the tree towards the receivers. Either a PIM (S,G)/
(S,G)/(*,G) tree or a mLDP P2MP or MP2MP LSP. (*,G) tree or a mLDP P2MP or MP2MP LSP.
LFA : Loop Free Alternate, a candidate UMH that can be used for the LFA: Loop Free Alternate as defined in [RFC5286]. In unicast Fast
secondary MoFRR path. 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.
RP: Rendezvous Point.
LSR: Label Switched Router.
BFD: Bidirectional Forwarding Detection.
IGP: Interior Gateway Protocol.
MVPN: Multicast Virtual Private Networks.
2. Basic Overview 2. Basic Overview
The basic idea of MoFRR is for a merge point router to join a 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 multicast tree via two divergent upstream paths in order to get
maximum redundancy. The two divergent paths SHOULD never merge maximum redundancy. The determination of this alternate upstream is
upstream, otherwise the maximal redundancy is compromised. Sometimes defined in Section 3.
the topology guarantees maximal redundancy, other times additional
configuration or techniques are needed to enforce it. See later in
this document.
A merge point router should only accept and forward on one of the In order to maximize robustness against any failure, the two paths
upstream paths at the time in order to avoid duplicate packet 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 forwarding. The selection of the primary and secondary UMH is done
by the MoFRR logic and normally based on unicast routing to find loop by the MoFRR logic and normally based on unicast routing to find loop
free candidates. free candidates. This is described in Section 4.
Note, the impact of additional amount of data on the network is Note, the impact of additional amount of data on the network is
mitigated when tree membership is densely populated. When a part of mitigated when tree membership is densely populated. When a part of
the network has redundant data flowing, join latency for new joining the network has redundant data flowing, join latency for new joining
members is reduced because its likely a tree merge point is not far members is reduced because its likely a tree Merge Point is not far
away. away.
3. Upstream Multicast Hop Selection 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
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 one 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 configured for non-ECMP-mode MoFRR for a Multicast tree
joins a primary path to its primary UMH and a secondary path to 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 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 used to reach the root of the tree. This is normally based on
unicast routing to find loop free candidate(s). With MoFRR unicast routing to find loop free candidate(s). With MoFRR
procedures we select a primary and a backup UMH. The procedures for procedures we select a primary and a backup UMH. The procedures for
determining the UMH are different for PIM and mLDP. See below; determining the UMH are different for PIM and mLDP. See below;
3.1. PIM 4.1. PIM
The UMH selection in PIM is also known as the Reverse Path Forwarding The UMH selection in PIM is also known as the Reverse Path Forwarding
(RPF) procedure. Based on a unicast route lookup on either the (RPF) procedure. Based on a unicast route lookup on either the
Source address or Rendezvous Point (RP) [RFC4601], an upstream Source address or Rendezvous Point (RP) [RFC4601], an upstream
interface is selected for sending the PIM Joins/Prunes AND accepting interface is selected for sending the PIM Joins/Prunes AND accepting
the multicast packets. The interface the packets are received on is 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 used to pass or fail the RPF check. If packets are received on an
interface that was not selected by the RPF procedure, or not the interface that was not selected by the RPF procedure, or not the
primary, the packets are discarded. primary, the packets are discarded.
3.2. mLDP 4.2. mLDP
The UMH selection in mLDP also depends on unicast routing, but the The UMH selection in mLDP also depends on unicast routing, but the
difference with PIM is that the acceptance of multicast packets is difference with PIM is that the acceptance of multicast packets is
based on MPLS labels and independent on the interface the packet is based on MPLS labels and independent of the interface the packet is
received on. Using the procedures as defined in [RFC6388] an received on. Using the procedures as defined in [RFC6388] an
upstream Label Switched Router (LSR) is elected. The upstream LSR upstream Label Switched Router (LSR) is elected. The upstream LSR
that was elected for a Label Switched Path (LSP) gets a unique local 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 allocated. Multicast packets are only forwarded if the
MPLS label matches the MPLS label that was allocated for that LSPs MPLS label matches the MPLS label that was allocated for that LSPs
(primary) upstream LSR. (primary) upstream LSR.
4. Topologies for MoFRR 5. Detecting Failures
MoFRR works best in topologies illustrated in the figure below. Once the two paths are established, the next step is detecting a
MoFRR may be enabled on any router in the network. In the figures failure on the primary path to know when to switch to the backup
below, MoFRR is shown enabled on the Provider Edge (PE) routers to path. This is a local issue but this section explore some
illustrate one way in which the technology may be deployed. 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
to build a new tree and hence are smaller. Sub-second to sub-200msec
switch-over should be possible.
6. MoFRR applicability
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.
6.1. Dual-Plane Topology
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.
4.1. Dual-Plane Topology
S S
P / \ P P / \ P
/ \ / \
^ G1 R1 ^ ^ G1 R1 ^
P / \ P P / \ P
/ \ / \
G2----------R2 ^ G2----------R2 ^
| \ | \ P | \ | \ P
^ | \ | \ ^ | \ | \
P | G3----------R3 P | G3----------R3
skipping to change at page 6, line 39 skipping to change at page 8, line 40
PE1 PE2 PE1 PE2
P = Primary path P = Primary path
S = Secondary path S = Secondary path
FIG1. Two-Plane Network Design FIG1. Two-Plane Network Design
The topology has two planes, a primary plane and a secondary plane 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. 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 This two plane design is common in service provider networks as it
eliminates single point of failures in their core network. The links eliminates single point of failures in their core network. The links
marked PJ indicate the normal path of how the PIM joins flow from the marked P indicate the normal path of how the PIM joins flow from the
POPs towards the source of the network. Multicast streams, POPs towards the source of the network. Multicast streams,
especially for the densely watched channels, typically flow along especially for the densely watched channels, typically flow along
both the planes in the network anyways. both the planes in the network anyway.
The only change MoFRR adds to this is on the links marked S where the 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 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 result of this, each PE router receives two copies of the same
stream, one from the primary plane and the other from the secondary stream, one from the primary plane and the other from the secondary
plane. As a result of normal UMH behavior, the multicast stream plane. As a result of normal UMH behavior, the multicast stream
received over the primary path is accepted and forwarded to the received over the primary path is accepted and forwarded to the
downstream receivers. The copy of the stream received from the downstream receivers. The copy of the stream received from the
secondary UNH is discarded. secondary UNH is discarded.
When a router detects a routing failure on the path to its its When a router detects a routing failure on the path to its primary
primary UMH, it will switch to the secondary UMH and accept packets UMH, it will switch to the secondary UMH and accept packets for that
for that stream. If the failure is repaired the router may switch stream. If the failure is repaired the router may switch back. The
back. The primary and secondary UMHs have only local context and not primary and secondary UMHs have only local context and not end-to-end
end-to-end context. context.
As one can see, MoFRR achieves the faster convergence by pre-building As one can see, MoFRR achieves the faster convergence by pre-building
the secondary multicast tree and receiving the traffic on that the secondary multicast tree and receiving the traffic on that
secondary path. The example discussed above is a simple case where secondary path. The example discussed above is a simple case where
there are two ECMP paths from each PE device towards the source, one 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 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 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 hold, and additional rules have to be taken into account to choose
when and where to join the secondary path. when and where to join the secondary path.
MoFRR is appealing in such topologies for the following reasons: MoFRR is appealing in such topologies for the following reasons:
1. Ease of deployment and simplicity: the functionality is only 1. Ease of deployment and simplicity: the functionality is only
required on the PE devices although it may be configured on all required on the PE devices although it may be configured on all
routers in the topology. Furthermore, each PE device can be routers in the topology. Furthermore, each PE device can be
enabled separately. PEs not enabled for MoFRR do not see any enabled separately, there is no need for a network wide
change or degradation. Inter-operability testing is not required coordination in order to deploy MoFRR. Inter-operability testing
as there are no PIM or mLDP protocol change. is not required as there are no PIM or mLDP protocol change.
2. End-to-end failure detection and recovery: any failure along the 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 path from the source to the PE can be detected and repaired with
the secondary disjoint stream. the secondary disjoint stream.(see Section 5 options 2, 3, 4)
3. Capacity Efficiency: as illustrated in the previous example, the 3. Capacity Efficiency: as illustrated in the previous example, the
Multicast trees corresponding to IPTV channels cover the backbone Multicast trees corresponding to IPTV channels cover the backbone
and distribution topology in a very dense manner. As a and distribution topology in a very dense manner. As a
consequence, the secondary path graft into the normal Multicast consequence, the secondary path graft into the normal Multicast
trees (ie. trees signaled by PIM or mLDP without MoFRR extension) trees (ie. trees signaled by PIM or mLDP without MoFRR extension)
at the aggregation level and hence do not demand any extra at the aggregation level and hence do not demand any extra
capacity either on the distribution links or in the backbone. capacity either on the distribution links or in the backbone.
They simply use the capacity that is normally used, without any They simply use the capacity that is normally used, without any
duplication. This is different from conventional FRR mechanisms duplication. This is different from conventional multicast FRR
which often duplicate the capacity requirements (the backup path mechanisms which often duplicate the capacity requirements when
crosses links/nodes which already carry the primary/normal tree the backup path crosses links/nodes which already carry the
and hence twice as much capacity is required). primary/normal tree and hence twice as much capacity is required.
4. Loop free: the secondary path join is sent on an ECMP disjoint 4. Loop free: the secondary path join is sent on an ECMP disjoint
path. By definition, the neighbor receiving this request is path. By definition, the neighbor receiving this request is
closer to the source and hence will not cause a loop. closer to the source and hence will not cause a loop.
The topology we just analyzed is very frequent and can be modeled as 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 per Fig2. The PE has two ECMP disjoint paths to the source. Each
ECMP path uses a disjoint plane of the network. ECMP path uses a disjoint plane of the network.
Source Source
/ \ / \
Plane1 Plane2 Plane1 Plane2
| | | |
A1 A2 A1 A2
\ / \ /
PE PE
skipping to change at page 8, line 27 skipping to change at page 10, line 29
Another frequent topology is described in Fig 3. PEs are grouped by Another frequent topology is described in Fig 3. PEs are grouped by
pairs. In each pair, each PE is connected to a different plane. 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 Each PE has one single shortest-path to a source (via its connected
plane). There is no ECMP like in Fig 2. However, there is clearly a plane). There is no ECMP like in Fig 2. However, there is clearly a
way to provide MoFRR benefits as each PE can offer a disjoint way to provide MoFRR benefits as each PE can offer a disjoint
secondary path to the other plane PE (via the disjoint path). secondary path to the other plane PE (via the disjoint path).
MoFRR secondary neighbor selection process needs to be extended in MoFRR secondary neighbor selection process needs to be extended in
this case as one cannot simply rely on using an ECMP path as this case as one cannot simply rely on using an ECMP path as
secondary neighbor. This extension is referred to as non-ecmp secondary neighbor. This extension is referred to as non-ecmp
extension and is described later in the document. extension and is described in Section 3.2.
Source Source
/ \ / \
Plane1 Plane2 Plane1 Plane2
| | | |
A1 A2 A1 A2
| | | |
PE1----PE2 PE1----PE2
FIG3. PEs are connected in pairs to Dual-Plane Backbone FIG3. PEs are connected in pairs to Dual-Plane Backbone
5. Detecting Failures 6.2. Capacity Planning for MoFRR
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.
The first (and simplest) option to detect a path failure is if a
directly connected link that is used as MoFRR UMH goes down. This
option can be used in combination with the other options as
documented below. 50msec switchover 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 switchover is possible.
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
to build a new tree and hence are smaller. Realistic availability
requirements (sub-second to sub-200msec) should be possible.
6. ECMP-mode MoFRR
If the IGP installs two ECMP paths to the source and if the Multicast
tree is enabled for ECMP-Mode MoFRR, the router installs them as
primary and secondary UMH. Only packets received from the primary
UMH path are processed. Packets received from the secondary UMH are
dropped.
The selected primary UMH should be the same as if MoFRR extension was
not enabled.
If more than two ECMP paths exist, two are selected as primary and
secondary UMH. Information from the IGP link-state topology could be
leveraged to optimize this selection.
Note, MoFRR does not restrict the number of UMH paths that are
joined. Implementations may use as many paths as are configured.
7. Non-ECMP-mode MoFRR
SourceS
/ \
/ \
Backbone
| |
| |
| |
X--------N
Fig5. Non-ECMP-Mode MoFRR
X is configured for MoFRR for a Multicast tree
R(X) is the primary UMH to S for X
N is a neighbor of X
R(N) is the LFA UMH to S for X
Router X in FIG5 has one primary path R(X) and one secondary LFA path
R(N) to reach the source. How it is determined that N is a LFA path
from X to S follows the procedures as documented in [RFC5286]. A
router X configured for non-ECMP-mode MoFRR for a Multicast tree
joins a primary path to its primary UMH R(X) and a secondary path to
LFA UMH N. Router X MUST stop joining the seconday path if the
following as described below occurs;
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). In order to
prevent control-plane loops a router MUST never setup a secondary
path to a LFA UMH if this UMH is the only member in the OIF list.
8. Keep It Simple Principle
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. PEs not enabled for MoFRR
do not see any change or degradation.
Multicast streams with Tight SLA requirements are often characterized
by a continuous high packet rate (SD video has a continuous
interpacket gap of ~ 3msec). MoFRR simply leverages the stream
characteristic to detect any failures along the primary branch and
switch-over on the secondary branch in a few 10s of msec.
9. Capacity Planning for MoFRR
As for LFA FRR (draft-ietf-rtgwg-lfa-applicability-00), MoFRR
applicability is topology dependent.
In this document, we have described two very frequent designs (Fig 2 The previous section has described two very frequent designs (Fig 2
and Fig 3) which provide maximum MoFRR benefits. and Fig 3) which provide maximum MoFRR benefits.
Designers with topologies different than Fig2 and 3 can still benefit Designers with topologies different than Fig2 and 3 can still benefit
from MoFRR benefits thanks to the use of capacity planning tools. from MoFRR thanks to the use of capacity planning tools.
Such tools are able to simulate the ability of each PE to build two 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 disjoint branches of the same tree. This for hundreds of PEs and
hundreds of sources. hundreds of sources.
This allows to assess the MoFRR protection coverage of a given This allows to assess the MoFRR protection coverage of a given
network, for a set of sources. network, for a set of sources.
If the protection coverage is deemed insufficient, the designer can If the protection coverage is deemed insufficient, the designer can
use such tool to optimize the topology (add links, change igp use such tool to optimize the topology (add links, change IGP
metrics). metrics).
10. Other Applications 6.3. 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.
6.4. Other Applications
While all the examples in this document show the MoFRR applicability While all the examples in this document show the MoFRR applicability
on PE devices, it is clear that MoFRR could be enabled on aggregation on PE devices, it is clear that MoFRR could be enabled on aggregation
or core routers. or core routers.
MoFRR can be popular in Data Center network configurations. With the MoFRR can be popular in Data Center network configurations. With the
advent of lower cost ethernet and increasing port density in routers, advent of lower cost ethernet and increasing port density in routers,
there is more meshed connectivity than ever before. When using a there is more meshed connectivity than ever before. When using a
3-level access, distribution, and core layers in a Data Center, there 3-level access, distribution, and core layers in a Data Center, there
is a lot of inexpensive bandwidth connecting the layers. This will is a lot of inexpensive bandwidth connecting the layers. This will
lend itself to more opportunities for ECMP paths at multiple layers. lend itself to more opportunities for ECMP paths at multiple layers.
This allows for multiple layers of redundancy protecting link and This allows for multiple layers of redundancy protecting link and
node failure at each layer with minimal redundancy cost. node failure at each layer with minimal redundancy cost.
Redundancy costs are reduced because only one packet is forwarded at Redundancy costs are reduced because only one packet is forwarded at
every link along the primary and secondary data paths so there is no every link along the primary and secondary data paths so there is no
duplication of data on any link thereby providing make-before-break duplication of data on any link thereby providing make-before-break
protection at a very small cost. protection at a very small cost.
Alternate methods to detect failures such as MPLS-OAM or BFD may be
considered.
The MoFRR principle may be applied to MVPNs. The MoFRR principle may be applied to MVPNs.
11. Security Considerations 7. IANA Considerations
This document makes no request of IANA.
8. Security Considerations
There are no security considerations for this design other than what There are no security considerations for this design other than what
is already in the main PIM specification [RFC4601] and mLDP is already in the main PIM specification [RFC4601] and mLDP
specification [RFC6388] . specification [RFC6388].
12. Acknowledgments 9. Acknowledgments
The authors would like to thank John Zwiebel, Greg Shepherd and Dave The authors would like to thank John Zwiebel, Greg Shepherd, Dave
Oran for their review of the draft. Oran and Alvaro Retana for their review of the draft.
13. Contributor Addresses 10. Contributor Addresses
Below is a list of other contributing authors in alphabetical order: Below is a list of other contributing authors in alphabetical order:
Nicolai Leymann Nicolai Leymann
Deutsche Telekom Deutsche Telekom
Winterfeldtstrasse 21 Winterfeldtstrasse 21
Berlin 10781 Berlin 10781
DE DE
Email: N.Leymann@telekom.de Email: N.Leymann@telekom.de
Jeff Tantsura Jeff Tantsura
Ericsson Ericsson
300 Holger Way 300 Holger Way
San Jose CA 95134 San Jose CA 95134
USA USA
14. References 11. References
14.1. Normative References
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP 11.1. Normative References
Specification", RFC 5036, October 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast [RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008. Reroute: Loop-Free Alternates", RFC 5286, September 2008.
14.2. Informative References 11.2. Informative References
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM): "Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006. Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC6388] Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas, [RFC6388] Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
"Label Distribution Protocol Extensions for Point-to- "Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, November 2011. 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 Authors' Addresses
Apoorva Karan Apoorva Karan
Cisco Systems, Inc. Cisco Systems, Inc.
3750 Cisco Way 3750 Cisco Way
San Jose CA, 95134 San Jose CA, 95134
USA USA
Email: apoorva@cisco.com Email: apoorva@cisco.com
Clarence Filsfils Clarence Filsfils
Cisco Systems, Inc. Cisco Systems, Inc.
De kleetlaan 6a De kleetlaan 6a
Diegem BRABANT 1831 Diegem BRABANT 1831
Belgium Belgium
Email: cfilsfil@cisco.com Email: cfilsfil@cisco.com
Dino Farinacci Dino Farinacci
Cisco Systems, Inc. lispers.net
425 East Tasman Drive
San Jose CA, 95134
USA USA
Email: dino@cisco.com Email: farinacci@gmail.com
IJsbrand Wijnands (editor) IJsbrand Wijnands (editor)
Cisco Systems, Inc. Cisco Systems, Inc.
De Kleetlaan 6a De Kleetlaan 6a
Diegem 1831 Diegem 1831
BE BE
Email: ice@cisco.com Email: ice@cisco.com
Bruno Decraene Bruno Decraene
France Telecom Orange
38-40 rue du General Leclerc 38-40 rue du General Leclerc
Issy Moulineaux cedex 9, 92794 Issy Moulineaux Cedex 9, 92794
FR FR
Email: bruno.decraene@orange.com Email: bruno.decraene@orange.com
Uwe Joorde Uwe Joorde
Deutsche Telekom Deutsche Telekom
Hammer Str. 216-226 Hammer Str. 216-226
Muenster D-48153 Muenster D-48153
DE DE
Email: Uwe.Joorde@telekom.de Email: Uwe.Joorde@telekom.de
Wim Henderickx Wim Henderickx
Alcatel-Lucent Alcatel-Lucent
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