Multicast-only Fast Reroute Based on Topology Independent Loop-free Alternate Fast Reroute
draft-liu-pim-mofrr-tilfa-01
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PIM Working Group Yisong Liu
Internet Draft Individual
Intended status: Standards Track M. McBride
Expires: May 23, 2020 Futurewei
Nov 23, 2019
Multicast-only Fast Reroute Based on Topology Independent Loop-free
Alternate Fast Reroute
draft-liu-pim-mofrr-tilfa-01
Status of this Memo
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This Internet-Draft will expire on May 23, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Abstract
Multicast-only Fast Reroute (MoFRR) has been defined in [RFC7431],
but the selection of the secondary multicast next hop only according
to the loop-free alternate fast reroute, which has restrictions in
multicast deployments. This document describes a mechanism for
Multicast-only Fast Reroute by using Topology Independent Loop-free
Alternate fast reroute, which is independent of network topology and
can achieve covering more network environments.
Table of Contents
1. Introduction ................................................ 2
1.1. Requirements Language .................................. 3
1.2. Terminology ............................................ 3
2. Problem Statement ........................................... 3
3. Solution .................................................... 5
3.1. Secondary UMH Selection in PIM ......................... 5
3.2. Secondary UMH Selection in MLDP ........................ 6
3.3. Extension Protocol Fields Conflict ..................... 6
4. Packet Format ............................................... 7
4.1. PIM Join Message Extension ............................. 7
4.2. MLDP Label Mapping Message Extension ................... 8
5. IANA Considerations ........................................ 11
6. Security Considerations .................................... 11
7. References ................................................. 12
7.1. Normative References .................................. 12
7.2. Informative References ................................ 13
8. Acknowledgments ............................................ 13
Authors' Addresses ............................................ 14
1. Introduction
As the deployment of video services, operators are paying more and
more attention to solutions that minimize the service disruption due
to faults in the IP network carrying the packets for these services.
Multicast-only Fast Reroute (MoFRR) has been defined in [RFC7431],
which can minimize multicast packet loss in a network when node or
link failures occur by making simple enhancements to multicast
routing protocols such as Protocol Independent Multicast (PIM) and
Multipoint LDP (mLDP). But the selection of the secondary multicast
next hop only according to the loop-free alternate fast reroute in
[RFC7431], and there are limitations in multicast deployments for
this mechanism. This document describes a new mechanism for
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Multicast-only Fast Reroute using Topology Independent Loop-free
Alternate (TILFA) fast reroute, which is independent of network
topology and can achieve covering more network environments.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Terminology
This document use the terms defined in [RFC7431], and also use the
concepts defined in [RFC7490]. The specific content of each term is
not described in this document.
2. Problem Statement
In [RFC7431] section 3, the secondary Upstream Multicast Hop (UMH)
of PIM and mLDP for MoFRR is a loop-free alternate (LFA). However,
the traditional LFA mechanism needs to satisfy at least one neighbor
whose next hop to the destination node is an acyclic next hop,
existing limitations in network deployments, and can only cover part
of the network topology environments. In some network topology, the
corresponding secondary UMH cannot be calculated, so PIM and MLDP
cannot establish a standby multicast tree and cannot implement MoFRR
protection. Therefore, the current MoFRR of PIM and MLDP is only
available in the network topology applicable to LFA.
The remote loop-free alternate (RLFA) defined in [RFC7490] is
extended from the LFA and can cover more network deployment
scenarios through the tunnel as an alternate path. The RLFA
mechanism needs to satisfy at least one node assumed to be N in the
network that the fault node is neither on the path from the source
node to the N node, nor on the path from the N node to the
destination node. RLFA only has enhancement compared to LFA but
still has limitations in network deployments.
[I-D.ietf-rtgwg-segment-routing-ti-lfa] defined a unicast FRR
solution based on the TILFA mechanism. The TILFA mechanism can
express the backup path with an explicit path, and has no constraint
on the topology, providing a more reliable FRR mechanism. The
unicast traffic can be forwarded according to the explicit path list
as an alternate path to implement unicast traffic protection, and
can achieve full coverage of various networking environments.
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The alternate path provided by the TILFA mechanism is actually a
Segment List, including one or more Adjacency SIDs of one or more
links between the P space and the Q space, and the NodeSID of P
space node. PIM and MLDP can look up the corresponding node IP
address in the unicast route according to the NodeSID, and the IP
addresses of the two endpoints of the corresponding link in the
unicast route according to the Adjacency SIDs, but the multicast
protocol packets cannot be directly sent along the path of the
Segment List.
Both the PIM join message and the MLDP Label Mapping message need to
be sent hop-by-hop to establish a standby multicast tree. However,
not all of the nodes and links on the unicast alternate path are
included in the Segment List. If the PIM and MLDP protocol packets
are transmitted only in unicast mode, then equivalently the PIM and
MLDP packets are transmitted through the unicast tunnel like unicast
traffic, and cannot pass through the intermediate nodes of the
tunnel. The intermediate nodes of the alternate path cannot forward
multicast traffic because there are no PIM or MLDP state entries on
the nodes. PIM needs to create entries on the device hop-by-hop and
generate an incoming interface and an outgoing interface list. MLDP
needs to create entries on the device hop-by-hop and generate an
incoming label and an outgoing label list. So it can form an end-to-
end complete multicast tree for forwarding multicast traffic.
Therefore, it is not possible to send PIM and MLDP packets like
unicast traffic according to the Segment List path and establish a
standby multicast tree.
It is available in principle that the path information of the
Segment List is added to the PIM and MLDP packets to guide the hop-
by-hop RPF selection. The IP address of the node corresponding to
the NodeSID can be used as the segmented root node, and the IP
addresses of the interfaces at both endpoints of the link
corresponding to the Adjacency SID can be used directly as the local
upstream interface and upstream neighbor, but there is currently no
field in protocol packet to carry the explicit path specified by the
Segment List. For the PIM protocol, the PIM RPF Vector attribute was
defined in [RFC5496], which can carry the node IP address
corresponding to the NodeSID. The Explicit RPF Vector was defined in
[RFC7891], which can carry the peer IP address corresponding to the
Adjacency SID, but if there are multiple same peer IP addresses
corresponding to the Adjacency SID (i.e. anycast IP address), the
upstream neighbor of RPF selection may be different from the actual
upstream link corresponding to the Adjacency SID, which can make the
PIM join path and the TILFA calculation path inconsistent. For the
MLDP protocol, there is also no field defined in the MLDP protocol
Label Mapping message that can carry the explicit path of the
Segment List.
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3. Solution
An Upstream Multicast Hop (UMH) is a candidate next-hop that can be
used to reach the root of the tree. In This document the secondary
UMH is based on unicast routing to find Segment List calculated by
TILFA. With MoFRR, The procedures for determining the secondary UMH
and establishing standby multicast tree are different for PIM and
mLDP.
This document extends the PIM and mLDP protocol, to establish the
standby multicast tree according to the Segment List calculated by
TILFA, and can achieve full coverage of various networking
environments for MoFRR protection of multicast services.
Assume that the Segment List calculated by TILFA is (NodeSID(A),
AdjSID(A-B)). Node A belongs to the P Space, and node B belongs to
the Q space. The IP address corresponding to NodeSID(A) can be
looked up in the local link state database of the IGP protocol, and
can be assumed to be IP-a. The IP addresses of the two endpoints of
the link corresponding to AdjSID(A-B) can also be looked up in the
local link state database of the IGP protocol, and can be assumed to
be IP-La and IP-Lb.
3.1. Secondary UMH Selection in PIM
In the procedure of PIM, IP-a can be looked as the normal RPF vector
attribute and added to the PIM join packet. IP-La and IP-Lb can be
looked as the RPF Vector attribute of the adjacency relationship,
called Adjacency RPF Vector, which is a new type of PIM join
attributes, and added to the PIM join packet too.
The PIM protocol firstly can select the RPF incoming interface and
upstream towards IP-a, and can join hop-by-hop to establish the PIM
standby multicast tree until the node A. On the node A, IP-Lb can be
looked as one PIM neighbor. If there are multiple PIM neighbors with
the same address IP-Lb, all of the corresponding local interfaces on
the node A need to be checked. The interface that is the only one
with the IP address IP-La can be looked as the RPF incoming
interface. The node A can send the PIM join packet to the node B on
the interface of IP-La, and IP-Lb is used as the RPF upstream
address of the PIM join.
After the PIM join packet is received on the node B, the PIM
protocol can find no more join attributes and select the RPF
incoming interface and upstream towards the multicast source
directly, and then can continue to join hop-by-hop to establish the
PIM standby multicast tree until the router directly connected the
source.
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3.2. Secondary UMH Selection in MLDP
In the procedure of MLDP, Explicit path TLV is newly defined in MLDP
Label Mapping message to carry IP-a, IP-La and IP-Lb, which is
contained in the field of Optional Parameters. IP-a can be looked as
the segmented root node address and is added as the Node Address Sub
TLV in the Explicit path TLV. IP-La and IP-Lb are added as the
Adjacency Address Sub TLV in the Explicit Path TLV.
The MLDP protocol can look up the upstream interface and the
upstream LSR in the unicast route to IP-a, and can send the Label
Mapping message hop-by-hop to establish the standby MPLS multicast
tree to the node A. After the message is received on the node A, the
Node Address Sub TLV corresponding to the IP-a can be deleted from
the Label Mapping message.
On the node A IP-Lb can be looked as one MLDP neighbor. If there are
multiple MLDP neighbors with the same address IP-Lb, all of the
corresponding local interfaces on the node A need to be checked. The
interface that is the only one with the IP address IP-La can be
looked as the upstream interface. The node A can send MLDP Label
mapping message to the node B, and IP-Lb is used as the upstream LSR
address.
After the message is received on the node B, the Adjacency Address
Sub TLV corresponding to the IP-La and IP-Lb is deleted from the
Label Mapping message and if there is no more any sub TLV in the
Explicit Path TLV then the TLV should be deleted. The MLDP protocol
can select the upstream interface and the upstream LSR in the
unicast route to the original root node directly, and can continue
to send the Label Mapping message to establish the standby MPLS
multicast tree to the original root node.
3.3. Extension Protocol Fields Conflict
PIM Adjacency RPF Vector attribute is newly defined in join
attributes. If there are conflicts from multiple downstream PIM
neighbors, the mechanism in [RFC5384] Section 3.3.3 can be used to
select a PIM downstream neighbor with a numerically smallest IP
address. If at least two neighbors have the same IP address, the
interface index MUST be used as a tie breaker.
In the Explicit Path TLV newly defined in MLDP Label Mapping
message, if there are conflicts from multiple downstream MLDP
neighbors, including the inconsistency of the Sub TLV types, and the
inconsistency of the Sub TLV contents, and the inconsistency of the
Sub TLV sequences, it is also recommended to use the mechanism in
[RFC5384] Section 3.3.3.
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4. Packet Format
This section describes the format of PIM and mLDP protocol packet
extension introduced by this document.
4.1. PIM Join Message Extension
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Family | Encoding Type | Rsrvd |S|W|R| Mask Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
|F|E| Attr_Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
|F|E| Attr_Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+.....
. . .
. . .
The original PIM join attribute already has been defined in
[RFC5384]
Attr_Type:
0- Vector ;
4- Explicit RPF Vector ;
Other existing definitions are not related to RPF Vector Attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-.......
The definition of Adjacency RPF Vector attribute
F bit: 0, indicating that the unrecognized device does not forward
the attribute
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E bit: indicates the last join attribute
Type: TBD
Length: depends on the address family of Encoded-Unicast address,
including the length of 2 addresses.
Value: Encoded-Unicast Address format defined in [RFC7761] Section
4.9.1, including 2 addresses. The first one indicates the address of
the local interface, and the second one indicates the address of the
peer interface. Only the case of the same address family is
supported.
4.2. MLDP Label Mapping Message Extension
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The LDP Label Mapping message format is defined in [RFC5036] Section
3.5.7. The MLDP P2MP protocol uses the message to establish a P2MP
multicast tree. The Optional Parameters field can be extended to
carry the node or link IP address list specified by the Segment
List.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value |
~ ~
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The TLV format definition in [RFC5036] Section 3.3 can be used for
the Explicit Path TLV carrying the specified path of the Segment
List.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| TBD1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Node Address Sub TLV |
| Adjacency Address Sub TLV |
~ ~
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The definition of Explicit Path TLV:
U bit: Unknown TLV bit. 1 indicates the unknown TLV MUST be silently
ignored and the rest of the message processed as if the unknown TLV
did not exist.
F bit: Forward unknown TLV bit. 0 indicates the unknown TLV is not
forwarded with the containing message.
Type: TBD1
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Length: contains all Sub-TLV lengths
Value: Contains one or more Sub-TLVs, which are recorded in the
order of TILFA's Segment List. There are two types of Sub TLVs now.
One of the two types is called Node Address Sub TLV which carries
the node IP address corresponding to the NodeSID, and the other is
called Adjacency Address Sub TLV which carries the local interface
address and the peer interface address corresponding to the
Adjacency SID.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|E| Type = TBD2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Node Address |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Node Address Sub TLV carrying the node IP address corresponding to
the NodeSID
U bit: 1 indicates the unknown TLV MUST be silently ignored and the
rest of the message processed as if the unknown TLV did not exist.
F bit: 0 indicates the unknown TLV is not forwarded with the
containing message.
E bit: 1 indicates the last Sub TLV.
Type: TBD2
Length: IPv4 address 4 octet, IPv6 address 16 octet
Value: The IP address of the node corresponding to the NodeSID in
the Segment List generated by TILFA
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|E| Type = TBD3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Local Interface Address |
| Remote Interface Address |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Adjacency Address Sub TLV carrying the local interface address and
the peer interface address corresponding to the Adjacency SID
U bit: 1 indicates the unknown TLV MUST be silently ignored and the
rest of the message processed as if the unknown TLV did not exist.
F bit: 0 indicates the unknown TLV is not forwarded with the
containing message.
E bit: 1 indicates the last Sub TLV.
Type: TBD3
Length: IPv4 address 8 octet, IPv6 address 32 octet
Value: The IP address of the local interface and the IP address of
the peer interface corresponding to the Adjacency SID in the Segment
List generated by TILFA must be recorded in order, and MUST be the
same address family.
5. IANA Considerations
This document requests IANA to assign a registry for Adjacency RPF
Vector in PIM Join Attribute and the Explicit Path TLV Node Address
Sub TLV, Adjacency Address Sub TLV in the Optional Parameters field
of MLDP P2MP Label Mapping message. The assignment is requested
permanent for IANA when this document is published as an RFC. The
string TBD, TBD1, TBD2 and TBD3 should all be replaced by the
assigned values accordingly.
6. Security Considerations
For general PIM-SM protocol Security Considerations, see [RFC7761].
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For general MLDP protocol Security Considerations, see [RFC6388]
TBD
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, October 2007
[RFC5286] Atlas, A., Ed., and A. Zinin, Ed., "Basic Specification
for IP Fast Reroute: Loop-Free Alternates", RFC 5286,
September 2008
[RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol
Independent Multicast (PIM) Join Attribute Format",
RFC 5384, November 2008
[RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
Forwarding (RPF) Vector TLV", RFC 5496, March 2009
[RFC6388] Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
Thomas, "Label Distribution Protocol Extensions for Point-
to-Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, November 2011
[RFC7431] Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B.
Decraene, "Multicast-Only Fast Reroute", RFC 7431, August
2015
[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, April 2015
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas,
I.,Parekh, R., Zhang, Z., and L. Zheng, "Protocol
IndependentMulticast - Sparse Mode (PIM-SM): Protocol
Specification(Revised)", RFC 7761, March 2016
[RFC7891] Asghar, J., Wijnands, IJ., Ed., Krishnaswamy, S., Karan,
A., and V. Arya, "Explicit Reverse Path Forwarding (RPF)
Vector", RFC 7891, June 2016
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, May 2017
[I-D.ietf-rtgwg-segment-routing-ti-lfa] Litkowski, S., Bashandy, A.,
Filsfils, C., Decraene, B., Francois, P., Voyer, D., Clad,
F., and P. Camarillo, "Topology Independent Fast Reroute
using Segment Routing", draft-ietf-rtgwg-segment-routing-
ti-lfa-01 (Expired), March 2019
7.2. Informative References
TBD
8. Acknowledgments
The authors would like to thank the following for their valuable
contributions of this document:
TBD
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Authors' Addresses
Yisong Liu
Individual
Email: liuyisong.ietf@gmail.com
Mike McBride
Futurewei Inc.
Email: michael.mcbride@futurewei.com
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