Network Working Group Quintin Zhao
Internet-Draft Tao Chou
Intended status: Standards Track Huawei Technology
Expires: April 25, 2013 Boris Zhang
Telus Communications
Emily Chen
October 22, 2012
P2MP Based mLDP Node Protection Mechanisms for Label Distribution
Protocol P2MP/MP2MP Label Switched Paths
draft-zhao-mpls-mldp-protections-03.txt
Abstract
Existing techniques provide a Point-to-point (P2P) Label Switch Path
(LSP) protection mechanism for mLDP nodes. In situations where the
data duplication along the p2p backup path is not acceptable, a
Point-To-Multipoint (P2MP) or Multipoint-To-Multipoint (MP2MP) LSPs
is needed, instead of a P2P LSPS, for the protection of mLDP nodes.
This document defines procedures and protocol extensions for
protection of mLDP nodes within Multi-Protocol Label Switching (MPLS)
networks using P2MP and MP2MP backup LSPs.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 25, 2013.
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirement Language . . . . . . . . . . . . . . . . . . . . . 4
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. mLDP Node Protection using mLDP LSPs . . . . . . . . . . . . . 7
4.1. Signaling Procedures for P2MP Based Node Protection . . . 8
4.1.1. Example of P2MP Based Node Protection's Procedure . . 8
4.1.2. Choose backup upstream LSR . . . . . . . . . . . . . . 10
4.1.3. Create backup path by MRT . . . . . . . . . . . . . . 11
4.1.4. PLR Switching Over Considerations . . . . . . . . . . 12
4.1.5. mLDP End-to-End Protection . . . . . . . . . . . . . . 12
4.2. Signaling Procedures for MP2MP Based Node Protection . . . 13
4.3. Protocol Extensions for mLDP Based Node Protection . . . . 15
4.3.1. mLDP Based MP Protection Capability Parameter TLV . . 15
4.3.2. mLDP Based MP Node Protection Status Elements . . . . 16
4.3.3. mLDP Backup FEC Element Encoding . . . . . . . . . . . 16
5. Signaling Procedures for mLDP Based Facility Node
Protection . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Manageability Considerations . . . . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Terminology
This document uses terminology discussed in [RFC6388] and [I-D.ietf-
mpls-ldp-multi-topology]. Additionally the following section
provides further explanation for key terms and terminology:
o PLR: The node where the traffic is logically redirected onto the
preset backup path is called Point of Local Repair (PLR).
o MP: The node where the backup path merges with the primary path is
called Merge Point (MP).
o N: The node be protected.
o Pn: The nodes on the backup path for protecting node N.
o MT-ID: A 16 bit value used to represent the Multi-Topology ID.
o Default MT Topology: A topology that is built using the MT-ID
default value of 0.
o MT Topology: A topology that is built using the corresponding
MT-ID.
o cut-link: A link whose removal partitions the network. A cut-link
by definition must be connected between two cut-vertices. If
there are multiple parallel links, then they are referred to as
cut-links in this document if removing the set of parallel links
would partition the network.
o cut-vertex: A vertex whose removal partitions the network.
o MRT: Maximally Redundant Trees. A pair of trees where the path
from any node X to the root R along the first tree and the path
from the same node X to the root along the second tree share the
minimum number of nodes and the minimum number of links. Each
such shared node is a cut-vertex. Any shared links are cut-links.
Any RT is an MRT but many MRTs are not RTs.
2. Requirement 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 [RFC2119].
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3. Introduction
In order to meet user's demands, operators and service providers
continue to deploy multicast applications using Multicast LDP (mLDP)
across MPLS networks. For the real-time applications, such as stock
trading, on-line games, and multimedia teleconferencing, traditional
IGP-mLDP convergence mechanisms fail to meet protection switching
times required to minimize, or negate entirely, application
interruptions.
Current best practice for protecting services, and subsequently
higher-layer applications, include the pre-computation and
establishment of a backup path. Once a failure has been detected on
the primary path, the traffic will be transmitted across the back-up
path.
However, two major challenges exist with the aforementioned solution.
The first is how to build an absolutely disjointed backup path for
each node in a multicast tree; the second is how to balance between
convergence time, resource consumption and network efficiency.
For a primary LDP P2MP/MP2MP LSP, there are several methods to set up
a backup path, these include:
o The use of an RSVP-TE P2P tunnel as a logical out-going interface,
consequently utilize the mature high availability technologies of
RSVP-TE.
o The use of an LDP P2P LSP as a packet encapsulation, so that the
complex configuration of P2P RSVP-TE can be skipped.
o Creating a P2MP/MP2MP backup LSP according to IGP's loop-free
alternative route. This solution avoids unnecessary packet
duplication compare to the use of a P2P LSP (which is specified in
the draft of I-D.wijnands-mpls-mldp-node-protection)and can have
100% scenario coverage if using with multi topology technology,
where the backup topology either can be statically configured or
dynamically computed/signaled mechanisms such the the mechanism
specified in the draft of [I-D.ietf-rtgwg-mrt-frr-architecture].
o Creation of Multiple Topology (MT) LSP using an entirely
disjointed topology.
When the backup path is present, there are two options for packet
forwarding and protection switchover:
o Option 1
The traffic sender transmits the stream on both the primary and
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backup path. Once the local traffic receiver detects a failure
the switchover will be relatively fast. However the disadvantage
of this method is that it consumes bandwidth as duplicate traffic
will be sent on the protection and backup path.
o Option 2
The traffic sender transmits only on the primary path. Although
bandwidth resource usage is minimized, cooperation is required to
provide adequate switching times and minimize high-layer
application impact. Noted that, some mechanisms may need create
more than one backup path, like the MRT, and need feed traffics on
all the backup paths. That means the MPs need to choose and
accept only one traffic of all in such case.
Ideally if switching time performance can be equal or better than the
Option 1, it is reasonable to choose option 2 to avoid bandwidth
wastage. Some recommendations of this document are based on this
viewpoint.
This document specifies P2MP/MP2MP LSP based mLDP node protection.
Note that the computation and configuration of the primary topology
and backup topology is out of the scope of this draft, the algorithm
can be either MRT based or any other algorithms/method available
including the static and offline tools. Besides, how to detect
failure is also outside the scope of this document, the mechanism can
be bidirectional or unidirectional forwarding detection for link or
target object.
3.1. Requirements
A number of requirements have been identified that allow the optimal
set of mechanisms to developed. These currently include:
o Computation of a disjointed (link and node) backup path within the
multicast tree;
o Minimization of protection convergence time;
o Minimization of operation and maintenance cost;
o Optimization of bandwidth usage;
o More protect scenarios can be covered.
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3.2. Scope
The method to detect failure is outside the scope of this document.
Also this document does not provide any authorization mechanism for
controlling the set of LSRs that may attempt to join a mLDP
protection session.
4. mLDP Node Protection using mLDP LSPs
By using IGP-FRR or Multi Topology Routing(including the MRT MT
routing), LDP can build the backup mLDP LSP among PLR, Pn, and MPs
(the downstream nodes of the protected node). In the cases where the
amount of downstream nodes are huge, this mechanism can avoid
unnecessary packet duplication on PLR, so that can protect the
network from traffic congestion risk.
+------------+ Point of Local Repair/
| R1 | Switchover Point
+------------+ (Upstream LSR)
/ \
/ \
10/ \20
/ \
/ \
/ \
+----------+ +-----------+
Protected Node | R2 | | R3 |
+----------+ +-----------+
| \ / |
| \ / |
| \ / |
10| 10\ /20 20|
| \ / |
| \ |
| / \ |
| / \ |
| / \ |
| / \ |
+-----------+ +-----------+ Merge Point
| R4 | | R5 | (Downstream LSR)
+-----------+ +-----------+
Figure 1: mLDP Local Protection using mLDP LSP Example
In Figure 1, R2 is on the preferential path from R4/5 to R1, and the
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secondary path is through R3. In this case, the mLDP LSP will be
established according to the IGP preferential path as R1--R2--R4/R5.
This section will take R2 as Protected Node for example, actually the
Protected Node can be any Transit node of the mLDP LSP. (We assume
that all the nodes in Figure 1 support this mLDP based node
protection method, including Pn.)
The procedure of P2MP/MP2MP Based mLDP Node Protection is as follows:
o As Protected Node, R2 should announce its selected upstream node
R1 to all its downstream nodes, which are R4 and R5 in this
example. How to know if one node should be protected can be
decided by local configuration or its role(transit) in the mLDP
LSP.
o R4 and R5 can consider R1 as the root node of the backup mLDP LSP,
and trigger the backup LSP signaling. In parallel, R4/R5 will
bind the primary NHLFE(s) to both the backup and primary ILM
entry, so that the traffic receiving from backup mLDP LSP can be
merged locally to the primary LSP.
o PLR can distinguish primary LSP and backup LSP by the signaling
procedure and only feed traffic on the primary path before
failure. When R2 node fails, R1 should switch the traffic to the
preset backup path quickly.
In this scenario, if R2 is protected by two P2P LSPs as R1--R3--R4
and R1--R3--R5, the traffic will be duplicated on R1, and R3 will
receive two streams. But, If R2 is protected by a mLDP LSP instead,
R3 will only receive one stream, and the packet duplication will be
done on R3.
The backup mLDP LSP can be P2MP/MP2MP LSP. The P2MP backup LSP is
used for P2MP LSP's node protection and the MP2MP backup LSP is used
for MP2MP LSP's node protection.
4.1. Signaling Procedures for P2MP Based Node Protection
This section introduces the signaling procedures of P2MP LSP's node
protection by backup P2MP LSP.
4.1.1. Example of P2MP Based Node Protection's Procedure
[Editors Note - This section introduces the procedures for P2MP Based
Node Protection desires the PLR being capable for node failure
detection.]
We assume all the involved nodes have advertised their corresponding
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protection capabilities. And the following in this section
demonstrates the signaling procedures of P2MP Based Node Protection.
STEP1 Normal procedure of setting up primary path:
Each non-Ingress LSR determine its own upstream LSR and sends
out label mapping message, following the procedures as
documented in [RFC6388] without any extension. And its
upstream LSR will propagate a new label mapping message to its
upstream LSR. In such case, we can say the non-Ingress LSR is
MP(as R4, R5 in Figure 1), MP's upstream LSR is protected
node(as R2 in Figure 1) and protected node's upstream node is
PLR(as R1 in Figure 1).
STEP2 Protected Node's procedure of setting up backup path:
After the Protected Node (R2) determines its upstream LSR
(R1), it will send the information(PLR's indentify, mLDP FEC)
in Notification messages to all its downstream nodes(MPs)
immediately. If there are other LSR(s) becoming its
downstream node(s) later, it will send such announcement for
its new MP(s).
STEP3 MP's procedure of setting up backup path:
When one MP (R4/R5) receive the Notification, it individually
determine its secondary paths toward R1 according to the IGP
results. Choosing which IGP mechanism's, LFA or MRT etc,
results is a local determination. After choosing the backup
upstream LSR, MP will send out a FRR Label mapping messages
including mLDP backup tree's key <PLR, protected-node,
original-mLDP-FEC> and MT-ID if backup path is not in the
default topology. Noted that, the label assigned for primary
path and secondary path MUST be different to avoid the MP
feeding the primary traffic to its secondary path's downstream
LSRs. In addition, the original-mLDP-FEC of the backup tree
key is encoded in a special opaque value as introduced in
section 4.2.3.
STEP4 Pn's procedure of setting up backup path:
When one node receives such aforementioned FRR label mapping
message, if it is not the PLR, it can consider itself as a Pn
node and will choose its backup upstream node toward PLR on
the corresponding topology's shortest IGP path. To avoid the
backup LSP going through the Protected Node, additional path
selection rule(s) should be applied. A simple method is that
the transit nodes can not choose the specified Protected Node
as its upstream LSR for the backup LSP. Other methods, such
as not-via policy, are under study, and will be added in the
future. In order to make the primary and backup topologies
rooted from PLR to satisfy the 'maximum disjointed'
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requirement, they can be either configured through static
configurations or be signaled dynamically through other
mechanisms such as MRT.
STEP5 PLR's procedures of setting up backup path:
When PLR(R1) receives the FRR label mapping message, it can
identify that it is the PLR by the mLDP backup FEC elements,
so it will decode the special opaque value(which contains the
primary mLDP FEC element, introduced in section 4.2.3) and
generate the backup forwarding entry for the specific LSP,
which is identified by the root address and opaque value in
the special opaque value, and bind the backup forwarding state
to the specific primary entry, which is indicated by the
Protected Node address in the message. Note that there might
be more than one backup forwarding entries for a specific
protected node.
STEP6 PLR's procedure when the Protected Node fails:
When failure is detected by PLR, it will switch the traffic to
the backup paths. MP will also locally choose to receive
which traffic and merge this traffic back to the primary LSP.
The switchover manner on PLR is specified in the later
section.
STEP7 Procedure after network re-converges:
When Merge Point(s) see the next hop to Root changed, it/they
will advertise the new mapping message(s), and the traffic
will re-converge to the new primary path. MP then withdraw
the backup label after finishing their re-converge. Pn will
delete the specified backup LSP like the procedure of deleting
normal P2MP LSP. And the entire backup P2MP LSP will be
deleted when all the node MP leave the backup P2MP LSP.
4.1.2. Choose backup upstream LSR
Obviously, the backup path can not go through the protected node N,
this section discusses how to choose the backup upstream LSR to avoid
N.
Firstly, finding out the candidate upstream LSRs as below:
o MPs should preferentially choose the upstream LSRs on the shortest
path as candidates, except node N. If no other upstream LSRs on
the shortest path, MPs should choose the next-hop on N's detour
path as candidate. The detour path can be IGP-FRR path or other
topologies' disjoint paths. The IGP-FRR path can be provided by
LFA, U-Turn, etc. The disjoint path can be provided by MT, MRT,
etc. How to choose the candidates is a local decision, can be
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determined by configuration.
o For the Pn node, it MUST choose from the IGP next-hops on the
shortest path toward PLR within the topology specified in the FRR
mLDP FEC element by MT-ID field. The candidate upstream LSRs MUST
except the node N.
Then, each node can choose one from the candidate upstream LSRs as
its backup upstream LSR, following the algorithm described in
[RFC6388] section 2.4.1.1.
4.1.3. Create backup path by MRT
The algorithm of Maximally Redundant Trees(MRTs), which is defined in
[I-D.enyedi-rtgwg-mrt-frr-algorithm], can compute two topologies(Blue
and Red) automatically. The two topologies can provide a pair of
maximally disjoint paths from one MP to PLR. The failed node will
not exist in both of the paths, unless it is the cut-vertex. So
these paths can be used as backup paths for the mLDP node protection.
Two backup multicast trees need be created along the MRT paths in
each MRT topologies, because sometimes MPs can not indentify which
path can avoid the failed node. The tree in one MRT topology also
uses the combination of <PLR, failed-node, original-mLDP-FEC> as its
own key, and the two trees in different topologies is distinguished
by MT-ID. The MRT backup tree's creation uses the same procedure
described as above.
The announcement with PLR's information from the protected node
triggers the MP to send backup mapping message along the MRT path in
both topologies, with corresponding tree's key, labels and MT-ID.
One node receives the backup message and find out it is not the PLR,
then it send out a new backup mapping message along the corresponding
path. If one node's multicast upstream node can only be the
protected node, this node can stop the procedure. When PLR receives
these messages, it associates the primary tree with the backup tree.
PLR may receive two backup trees if both paths can avoid the
protected node.
Because one MRT tree may not include all MPs, PLR must feeds the
traffics to both corresponding backup trees once PLR detects the
failure. And MPs may receive packets from both MRT paths, MPs MUST
drop the packets in the Red topology in such case.
MRT makes the solution more complex, but it can be deployed
automatically and reach 100 percent scenario coverage in theory.
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4.1.4. PLR Switching Over Considerations
The P2MP Based Node Protection also has the BFD scalability issue on
the Protected node. Similar with P2P Based Node Protection solution,
this section provides two methods for deployment.
o Option 1:
If PLR cannot differentiate link and node failure, MP must take
the responsibility to drop one of the two reduplicate traffics
when failure is detected. In this case, the Node Failure Required
Flag, in the P2MP Based MP Node Protection Status Element, must be
set as 'N'. PLR will switch the traffic to the backup path when
failure detected and MP will drop traffic on the backup path until
it sees N fails.
o Option 2:
If PLR can differentiate link and node failure, PLR MUST NOT
switch the traffic to the backup path until it detects the node N
failure. In this case, the Node Failure Required Flag, in the
P2MP Based MP Node Protection Status Element, must be set as 'Y'.
Note that, all the MPs of N MUST use one same Node Failure Required
Flag value. Otherwise, the backup P2MP LSP tree need depart to two
trees different from the switch over type, and this part is TBD. And
it is also possible that can use a backup MP2MP LSP tree to protect
one node in the primary MP2MP LSP tree, this part is TBD too
[Editors Note - This Editors note and remaining options will be
removed before publication of this document.]
4.1.5. mLDP End-to-End Protection
[I-D.ietf-mpls-ldp-multi-topology] provides the mechanism to setup
disjointed LSPs within different topologies. Applications can use
these redundant LSPs for end-to-end protection based on MT.
The backup topologies can be build by static configuration or
automatic computation. The static method need create the disjoint
trees artificially in one topology, root node can setup 1:1 or 1+1
End-to-End protection, using these backup disjoint mLDP LSP. The
automatic method can use MRT algorithm. MRT can also provide
maximally disjoint P2P paths to build a pair of redundant multicast
trees from leaves to root. This section mainly analyses the
automatic method.
The procedure of building backup multicast trees by MRT just like the
creation of primary multicast tree. Leaf triggers building multicast
tree along the path toward root in both MRT topologies, colored as
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Blue and Red, separately.
Each MRT backup tree can cover all the leaves, but two different sets
of leaves maybe share one same mid node(not the cut-vertex).
Therefore, the root must feed traffic to both two MRT trees when
failure, and the leaves must drop the packets in the Red topology if
receives packets on both MRT backup tree.
Take Figure 2 for example, node R is the root and the other nodes are
leaves. When the node G breaks, node F,D will not receive traffic in
Blue MRT and node E,B will not receive traffic in Red MRT.
Therefore, only feeds traffics in both MRTs can protect all leaves.
In addition, node A,C can receive traffics in both MRTs, they must
choose dropping the one in Red MRT.
[A]---[R]---[B]---+ [A]<--[R]-->[B]---+ [A] [R] [B]
| | | | | | | ^ | ^
| | | | V | V | V |
[C]---[D] | [E] [C] [D] | [E] [C]<--[D] | [E]
| | | ^ | | | ^
| | | | V V | |
[F]---[G]---+ [F]<--[G] [F]-->[G]---+
(a) Original topology (b) Blue MRT of root R (c) Red MRT of root R
Figure 2: mLDP End-to-End Protection using MRT
Because MRT computation is separate in different areas, in the case
of inter-area, root and leaves are not in the same area, the
BR(Border Router) must do some special procedure for protecting
another BR. For example, BR1 and BR2 cross the area(x) and area(y).
Root is in area(y). One node, LSR1, in area(x) may choose BR1 as its
Red MRT upstream LSR to against BR2's failure. But maybe BR1 will
choose BR2 as its Red MRT upstream LSR in area(y). LSR1 will receive
no traffic when BR2 fails. To solving such problem, BR can choose to
treat itself as a leaf when it receives the mLDP mapping message,
which need cross areas, in MRT topology. That means BR needs to join
both the Blue and Red MRT trees in such case, and drops the Red MRT's
traffic if it receives traffic in both MRTs.
In order to reduce the packets' loss in convergence, End-to-End
Protection also needs leaves to support MBB procedure.
4.2. Signaling Procedures for MP2MP Based Node Protection
This section introduces the solution to protect MP2MP LSP node by
backup MP2MP LSP.
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The procedure is similar with the P2MP based node protection. MP
send backup label mapping message with MP2MP downstream FRR FEC
element. When PLR receives backup label mapping message with MP2MP
downstream flag, it send the backup label mapping message with mp2mp
upstream FRR FEC element to Pn, and then finally to MPs. This
procedure just follows the normal MP2MP LSP procedure.
PLR node binds its backup MP2MP downstream NHLFE entry to primary
MP2MP downstream ILM entry and binds its primary MP2MP upstream NHLFE
entry to backup MP2MP upstream ILM entry.
MP node binds its primary MP2MP downstream NHLFE entry to backup
MP2MP downstream ILM entry and binds its backup MP2MP upstream NHLFE
entry to primary MP2MP upstream ILM entry.
Once detecting the protected node failure, PLR switches the
downstream traffic to backup path and MP switches the upstream
traffic to backup path.
End-to-End protection can also use the backup multicast tree to
protect MP2MP applications. The biggest difference between End-to-
End and Node protection is the detecting method, which is outside the
scope of this document. In addition, the MRT may not suitable for
MP2MP End-to-End protection at present. The disjoint path from leaf
to root can not provide protection for the traffic from leaf to leaf.
Because the upstream traffic sent from leaf to leaf include two
directions, downstream and upstream. One node may be another one's
downstream LSR in both directions of both MRT topologies.
For example in figure 3, node R is the root and the other nodes are
leaves of the MP2MP LSPs. The downstream traffic from root to leaves
is along the path shown in sub figure (b) and (c), and the upstream
traffic from leaf G to other nodes is along the path shown in sub
figure (e) and (f). Obviously, if the node F breaks, the node D can
not receive the traffic sent by leaf G in both MRT topologies.
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[A]---[R]---[B] [A]<--[R]-->[B] [A] [R] [B]
| | | | | ^ | ^
| | | V | | V |
[C]---[D] | [C] [D] | [C]<--[D] |
| | ^ | | |
| | | V V |
[F]---[G] [F]<--[G] [F]-->[G]
(a) Original topology (b) Blue MRT of root R (c) Red MRT of root R
[A]<--[R]<--[B] [A] [R] [B]
| ^ ^ ^ ^
V | | | |
[C] [D] | [C]<--[D] |
^ | ^ |
| | | |
[F]<--[G] [F]<--[G]
(e) Blue MRT of root G (f) Red MRT of root G
Figure 3: The problem of MP2MP End-to-End Protection using MRT
[TBD]This section is still in research, the details will be shown in
the future versions.
4.3. Protocol Extensions for mLDP Based Node Protection
4.3.1. mLDP Based MP Protection Capability Parameter TLV
A new Capability Parameter TLV is defined as mLDP Based MP Protection
Capability for node protection. Following is the format of this new
Capability Parameter TLV:
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| mLDP Based MP Prot.(IANA) | Length (= 2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+
S: As specified in [RFC5561]
Figure 4: mLDP Based MP Protection Capability
This is an unidirectional capability announced.
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An LSR, which supports the mLDP based protection procedures, should
advertise this mLDP Based MP Protection Capability TLV to its LDP
speakers. Without receiving this capability announcement, an LSR
MUST NOT send any message including the mLDP Based MP Node Protection
Status Element and mLDP Backup FEC Element to its peer.
Capability Data might be needed to distinguish the capabilities of
different nodes, such as PLR, MP, N, Pn and so on. This part is TBD.
4.3.2. mLDP Based MP Node Protection Status Elements
A new type of LDP MP Status Value Element is introduced, for
notifying upstream LSR information. It is encoded as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|mLDP FRR Type=3| Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ PLR Node Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: FRR LDP MP Status Value Element
mLDP FRR Type: Type 3 (to be assigned by IANA)
Length: If the Address Family is IPv4, the Length MUST be 5;
if the Address Family is IPv6, the Length MUST be 17.
PLR Node Address: The host address of the PLR Node.
4.3.3. mLDP Backup FEC Element Encoding
A new type of mLDP backup FEC Element is introduced, for notifying
upstream LSR information. It is encoded as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|mLDP FEC T=FRR | Address Family | Address Length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ PLR Node Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N| Status code | FEC-Type | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protected Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Length | Opaque Value ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: mLDP Backup FEC Element
mLDP FEC Type-FRR: Type 5 (to be assigned by IANA)
Length: If the Address Family is IPv4, the Address Length MUST be 9;
if the Address Family is IPv6, the Address Length MUST be 33.
Status code: 1 = Primary path for traffic forwarding
2 = Secondary path for traffic forwarding
FEC-Type: 6 = P2MP FEC type
7 = MP2MP-up FEC type
8 = MP2MP-down FEC type
PLR Node Address: The host address of the PLR Node.
Protected Node Address: The host address of the Protected Node.
N Bit: Node Failure Required Flag, the occasion of switching traffic's on PLR
1 = 'Y', switch traffic to backup path only when PLR detects the node failure
0 = 'N', switch traffic to backup path when PLR detects failure
Opaque Length: The length of the opaque value, in octets.
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Opaque Value: One or more MP opaque value elements, the same definition in [RFC6388].
Specially for the FRR mLDP FEC element, the Opaque Value MUST be encoded
as the Recursive Opaque Value, which is defined in [RFC6512]. The value
fields of the Recursive Opaque Value contains the original primary
path's mLDP FEC element.
The encoding for this Recursive Opaque Value, as defined in [RFC6512], is shown in Figure 5.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 7 | Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ ~
| P2MP or MP2MP FEC Element |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Recursive Opaque Value, defined in [RFC6512]
The Opaque Value is encoded by MP node and decoded by PLR. Other
nodes MUST NOT interpret the opaque value at all.
5. Signaling Procedures for mLDP Based Facility Node Protection
[TBD]In the detour solution, one backup LSP protects one primary one.
So if there are several mLDP LSPs using one backup path, there will
be several backup LSPs on one same backup path. In such case, this
may cause one kind waste of LSP resource. Using the facility node
protection solution can minimize such waste, the cost is making the
procedure more complicated.
MP chooses its primary upstream LSR as N and send label mapping
message to N. When N receives the label mapping message from MP, it
will assign a upstream label to MP. MP uses this upstream label as
its incoming label and release the label resource it used for this
LSP before. Then MP will find the backup mLDP LSP by the specified
PLR and N address, if no such LSP exists, MP will trigger creating
one. The backup mLDP LSP is exclusive by PLR and N address. N uses
this upstream label as its own incoming label and send this label's
label mapping message to PLR. After PLR create the primary LSP, it
will find one backup mLDP LSP by the specified PLR and N address. If
there exists one such LSP, PLR will bind the backup LSP to primary
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one.
When PLR detects the N's failure, it switches traffic to backup path
using dual label stack, the inner label is the outgoing label from N
and the outer label is the backup LSP's outgoing label from Pn. MP
will receive the traffic from Pn, which is same as the traffic from
N.
The key point of the facility solution is node N how to assign the
upstream label. This solution is still under research.
6. IANA Considerations
This memo includes the following requests to IANA:
o mLDP Based MP Protection Capability.
o mLDP FRR types for LDP MP Status Value Element.
o mLDP FEC FRR Element type.
7. Manageability Considerations
[Editors Note - This section is TBD.]
8. Security Considerations
The same security considerations apply as for the base LDP
specification, as described in [RFC5036]. The protocol extensions
specified in this document do not provide any authorization mechanism
for controlling the set of LSRs that may attempt to join a mLDP
protection session. If such authorization is desirable, additional
mechanisms, outside the scope of this document, are needed.
Note that authorization policies should be implemented and/or
configure at all the nodes involved.
Note that authorization policies should be implemented and/or
configure at all the nodes involved.
9. Acknowledgements
We would like to thank Nicolai Leymann and Daniel King for his
valuable suggestions regarding to this draft. We also would like to
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thank Robin Li, Lujun Wan for their comments and suggestions to the
draft.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
Le Roux, "LDP Capabilities", RFC 5561, July 2009.
[RFC6348] Le Roux, JL. and T. Morin, "Requirements for Point-to-
Multipoint Extensions to the Label Distribution Protocol",
RFC 6348, September 2011.
[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.
[RFC6512] Wijnands, IJ., Rosen, E., Napierala, M., and N. Leymann,
"Using Multipoint LDP When the Backbone Has No Route to
the Root", RFC 6512, February 2012.
10.2. Informative References
[I-D.ietf-mpls-ldp-multi-topology]
Zhao, Q., Fang, L., Zhou, C., Li, L., and N. So, "LDP
Extensions for Multi Topology Routing",
draft-ietf-mpls-ldp-multi-topology-04 (work in progress),
July 2012.
[I-D.wijnands-mpls-mldp-node-protection]
Wijnands, I., Rosen, E., Raza, K., Tantsura, J., Atlas,
A., and Q. Zhao, "mLDP Node Protection",
draft-wijnands-mpls-mldp-node-protection-01 (work in
progress), June 2012.
[I-D.ietf-rtgwg-mrt-frr-architecture]
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Atlas, A., Kebler, R., Envedi, G., Csaszar, A.,
Konstantynowicz, M., White, R., and M. Shand, "An
Architecture for IP/LDP Fast-Reroute Using Maximally
Redundant Trees", draft-ietf-rtgwg-mrt-frr-architecture-01
(work in progress), March 2012.
[I-D.enyedi-rtgwg-mrt-frr-algorithm]
Atlas, A., Envedi, G., Csaszar, A., and A. Gopalan,
"Algorithms for computing Maximally Redundant Trees for
IP/LDP Fast- Reroute",
draft-enyedi-rtgwg-mrt-frr-algorithm-02 (work in
progress), October 2012.
Authors' Addresses
Quintin Zhao
Huawei Technology
125 Nagog Technology Park
Acton, MA 01719
US
Email: quintin.zhao@huawei.com
Tao Chou
Huawei Technology
156 Beiqing Rd
Haidian District, Beijing 100095
China
Email: tao.chou@huawei.com
Boris Zhang
Telus Communications
200 Consilium Pl Floor 15
Toronto, ON M1H 3J3
Canada
Phone:
Email: Boris.Zhang@telus.com
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Emily Chen
2717 Seville Blvd, Apt 1205
Clearwater, FL 33764
US
Email: emily.chen220@gmail.com
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