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IETF RFC 7140
Last modified on Sunday, March 2nd, 2014
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Internet Engineering Task Force (IETF) L. Jin
Request for Comments: 7140
Category: Standards Track F. Jounay
ISSN: 2070-1721 Orange CH
IJ. Wijnands
Cisco Systems, Inc
N. Leymann
Deutsche Telekom AG
March 2014
LDP Extensions for Hub and Spoke Multipoint Label Switched Path
 Abstract
This document introduces a hub and spoke multipoint (HSMP) Label
Switched Path (LSP), which allows traffic from root to leaf through
point-to-multipoint (P2MP) LSPs and also leaf to root along the
reverse path. That means traffic entering the HSMP LSP from the
application/customer at the root node travels downstream to each leaf
node, exactly as if it were traveling downstream along a P2MP LSP to
each leaf node. Upstream traffic entering the HSMP LSP at any leaf
node travels upstream along the tree to the root, as if it were
unicast to the root. Direct communication among the leaf nodes is
not allowed.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7140.
Jin, et al. Standards Track PAGE 1 
RFC 7140 LDP Extensions for HSMP LSP March 2014
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Setting Up HSMP LSP with LDP . . . . . . . . . . . . . . . . 4
3.1. Support for HSMP LSP Setup with LDP . . . . . . . . . . . 4
3.2. HSMP FEC Elements . . . . . . . . . . . . . . . . . . . . 5
3.3. Using the HSMP FEC Elements . . . . . . . . . . . . . . . 5
3.4. HSMP LSP Label Map . . . . . . . . . . . . . . . . . . . 6
3.4.1. HSMP LSP Leaf Node Operation . . . . . . . . . . . . 7
3.4.2. HSMP LSP Transit Node Operation . . . . . . . . . . . 7
3.4.3. HSMP LSP Root Node Operation . . . . . . . . . . . . 8
3.5. HSMP LSP Label Withdraw . . . . . . . . . . . . . . . . . 9
3.5.1. HSMP Leaf Operation . . . . . . . . . . . . . . . . . 9
3.5.2. HSMP Transit Node Operation . . . . . . . . . . . . . 9
3.5.3. HSMP Root Node Operation . . . . . . . . . . . . . . 10
3.6. HSMP LSP Upstream LSR Change . . . . . . . . . . . . . . 10
3.7. Determining Forwarding Interface . . . . . . . . . . . . 10
4. HSMP LSP on a LAN . . . . . . . . . . . . . . . . . . . . . . 11
5. Redundancy Considerations . . . . . . . . . . . . . . . . . . 11
6. Failure Detection of HSMP LSP . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. New LDP FEC Element Types . . . . . . . . . . . . . . . . 12
8.2. HSMP LSP Capability TLV . . . . . . . . . . . . . . . . . 13
8.3. New Sub-TLVs for the Target Stack TLV . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14
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RFC 7140 LDP Extensions for HSMP LSP March 2014
1. Introduction
The point-to-multipoint (P2MP) Label Switched Path (LSP) defined in
[RFC 6388] allows traffic to transmit from root to several leaf nodes,
and multipoint-to-multipoint (MP2MP) LSP allows traffic from every
node to transmit to every other node. This document introduces a hub
and spoke multipoint (HSMP) LSP, which has one root node and one or
more leaf nodes. An HSMP LSP allows traffic from root to leaf
through downstream LSP and also leaf to root along the upstream LSP.
That means traffic entering the HSMP LSP at the root node travels
along the downstream LSP, exactly as if it were traveling along a
P2MP LSP, and traffic entering the HSMP LSP at any other leaf nodes
travels along the upstream LSP toward only the root node. The
upstream LSP should be thought of as a unicast LSP to the root node,
except that it follows the reverse direction of the downstream LSP,
rather than the unicast path based on the routing protocol. The
combination of upstream LSPs initiated from all leaf nodes forms a
multipoint-to-point LSP.
2. Terminology
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].
This document uses the following terms and acronyms:
mLDP: Multipoint extensions for Label Distribution Protocol (LDP)
defined in [RFC 6388].
P2MP LSP: point-to-multipoint Label Switched Path. An LSP that
has one Ingress Label Switching Router (LSR) and one or more
Egress LSRs.
MP2MP LSP: multipoint-to-multipoint Label Switched Path. An LSP
that connects a set of nodes, such that traffic sent by any node
in the LSP is delivered to all others.
HSMP LSP: hub and spoke multipoint Label Switched Path. An LSP
that has one root node and one or more leaf nodes, allows traffic
from the root to all leaf nodes along the downstream P2MP LSP and
also leaf to root node along the upstream unicast LSP.
FEC: Forwarding Equivalence Class
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3. Setting Up HSMP LSP with LDP
An HSMP LSP is similar to MP2MP LSP described in [RFC 6388], with the
difference being that, when the leaf LSRs send traffic on the LSP,
the traffic is first delivered only to the root node and follows the
upstream path from the leaf node to the root node. The root node
then distributes the traffic on the P2MP tree to all of the leaf
nodes.
An HSMP LSP consists of a downstream path and upstream path. The
downstream path is the same as P2MP LSP, while the upstream path is
only from leaf to root node, without communication between the leaf
nodes themselves. The transmission of packets from the root node of
an HSMP LSP to the receivers (the leaf nodes) is identical to that of
a P2MP LSP. Traffic from a leaf node to the root follows the
upstream path that is the reverse of the path from the root to the
leaf. Unlike an MP2MP LSP, traffic from a leaf node does not branch
toward other leaf nodes, but it is sent direct to the root where it
is placed on the P2MP path and distributed to all leaf nodes
including the original sender.
To set up the upstream path of an HSMP LSP, ordered mode MUST be
used. Ordered mode can guarantee that a leaf will start sending
packets to the root immediately after the upstream path is installed,
without being dropped due to an incomplete LSP.
3.1. Support for HSMP LSP Setup with LDP
An HSMP LSP requires the LDP capabilities [RFC 5561] for nodes to
indicate that they support setup of HSMP LSPs. An implementation
supporting the HSMP LSP procedures specified in this document MUST
implement the procedures for Capability Parameters in Initialization
messages. Advertisement of the HSMP LSP Capability indicates support
of the procedures for HSMP LSP setup.
A new Capability Parameter TLV is defined, the HSMP LSP Capability
Parameter. Below is the format of the HSMP LSP Capability Parameter.
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| HSMP LSP Cap (0x0902) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+
Figure 1: HSMP LSP Capability Parameter Encoding
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U-bit: Unknown TLV bit, as described in [RFC 5036]. The value MUST
be 1. 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, as described in [RFC 5036]. The
value of this bit MUST be 0 since a Capability Parameter TLV
is sent only in Initialization and Capability messages, which
are not forwarded.
Length: SHOULD be 1.
S-bit: As defined in Section 3 of [RFC 5561].
Reserved: As defined in Section 3 of [RFC 5561].
HSMP LSP Capability Parameter type: 0x0902.
If the peer has not advertised the corresponding capability, then
label messages using the HSMP Forwarding Equivalence Class (FEC)
Element SHOULD NOT be sent to the peer (as described in Section 2.1
of [RFC 6388]). Since ordered mode is applied for HSMP LSP signaling,
the label message break would ensure that the initiating leaf node is
unable to establish the upstream path to root node.
3.2. HSMP FEC Elements
We define two new protocol entities: the HSMP Downstream FEC Element
and Upstream FEC Element. If a FEC TLV contains one of the HSMP FEC
Elements, the HSMP FEC Element MUST be the only FEC Element in the
FEC TLV. The structure, encoding, and error handling for the HSMP-
downstream FEC Element and HSMP-upstream FEC Element are the same as
for the P2MP FEC Element described in Section 2.2 of [RFC 6388]. The
difference is that two additional new FEC types are defined: HSMP-
downstream FEC (10) and HSMP-upstream FEC (9).
3.3. Using the HSMP FEC Elements
The entries in the list below describe the processing of the HSMP FEC
Elements. Additionally, the entries defined in Section 3.3 of
[RFC 6388] are also reused in the following sections.
1. HSMP downstream LSP <X, Y> (or simply downstream <X, Y>): an
HSMP LSP downstream path with root node address X and opaque
value Y.
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2. HSMP upstream LSP <X, Y> (or simply upstream <X, Y>): an HSMP
LSP upstream path for root node address X and opaque value Y
that will be used by any downstream node to send traffic
upstream to root node.
3. HSMP-downstream FEC Element <X, Y>: a FEC Element with root node
address X and opaque value Y used for a downstream HSMP LSP.
4. HSMP-upstream FEC Element <X, Y>: a FEC Element with root node
address X and opaque value Y used for an upstream HSMP LSP.
5. HSMP-D Label Mapping <X, Y, L>: A Label Mapping message with a
single HSMP-downstream FEC Element <X, Y> and label TLV with
label L. Label L MUST be allocated from the per-platform label
space of the LSR sending the Label Mapping Message.
6. HSMP-U Label Mapping <X, Y, Lu>: A Label Mapping message with a
single HSMP upstream FEC Element <X, Y> and label TLV with label
Lu. Label Lu MUST be allocated from the per-platform label
space of the LSR sending the Label Mapping Message.
7. HSMP-D Label Withdraw <X, Y, L>: a Label Withdraw message with a
FEC TLV with a single HSMP-downstream FEC Element <X, Y> and
label TLV with label L.
8. HSMP-U Label Withdraw <X, Y, Lu>: a Label Withdraw message with
a FEC TLV with a single HSMP-upstream FEC Element <X, Y> and
label TLV with label Lu.
9. HSMP-D Label Release <X, Y, L>: a Label Release message with a
FEC TLV with a single HSMP-downstream FEC Element <X, Y> and
Label TLV with label L.
10. HSMP-U Label Release <X, Y, Lu>: a Label Release message with a
FEC TLV with a single HSMP-upstream FEC Element <X, Y> and label
TLV with label Lu.
3.4. HSMP LSP Label Map
This section specifies the procedures for originating HSMP Label
Mapping messages and processing received HSMP Label Mapping messages
for a particular HSMP LSP. The procedure of a downstream HSMP LSP is
similar to that of a downstream MP2MP LSP described in [RFC 6388].
When LDP operates in Ordered Label Distribution Control mode
[RFC 5036], the upstream LSP will be set up by sending an HSMP LSP LDP
Label Mapping message with a label that is allocated by the upstream
LSR to its downstream LSR hop-by-hop from root to leaf node,
installing the upstream forwarding table by every node along the LSP.
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The detailed procedure of setting up upstream HSMP LSP is different
than that of upstream MP2MP LSP, and it is specified in the remainder
of this section.
All labels discussed here are downstream-assigned [RFC 5332] except
those that are assigned using the procedures described in Section 4.
Determining the upstream LSR for the HSMP LSP <X, Y> follows the
procedure for a P2MP LSP described in Section 2.4.1.1 of [RFC 6388].
That is, a node Z that wants to join an HSMP LSP <X, Y> determines
the LDP peer U that is Z's next hop on the best path from Z to the
root node X. If there are multiple upstream LSRs, a local algorithm
should be applied to ensure that there is exactly one upstream LSR
for a particular LSP.
To determine one's HSMP downstream LSR, an upstream LDP peer that
receives a Label Mapping with the HSMP-downstream FEC Element from an
LDP peer D will treat D as HSMP downstream LDP peer.
3.4.1. HSMP LSP Leaf Node Operation
The leaf node operation is much the same as the operation of MP2MP
LSP defined in Section 3.3.1.4 of [RFC 6388]. The only difference is
the FEC elements as specified below.
A leaf node Z of an HSMP LSP <X, Y> determines its upstream LSR U for
<X, Y> as per Section 3.3, allocates a label L, and sends an HSMP-D
Label Mapping <X, Y, L> to U. Leaf node Z expects an HSMP-U Label
Mapping <X, Y, Lu> from node U and checks whether it already has
forwarding state for upstream <X, Y>. If not, Z creates forwarding
state to push label Lu onto the traffic that Z wants to forward over
the HSMP LSP. How it determines what traffic to forward on this HSMP
LSP is outside the scope of this document.
3.4.2. HSMP LSP Transit Node Operation
The procedure for processing an HSMP-D Label Mapping message is much
the same as that for an MP2MP-D Label Mapping message defined in
Section 3.3.1.5 of [RFC 6388]. The processing of an HSMP-U Label
Mapping message is different from that of an MP2MP-U Label Mapping
message as specified below.
Suppose node Z receives an HSMP-D Label Mapping <X, Y, L> from LSR D.
Z checks whether it has forwarding state for downstream <X, Y>. If
not, Z determines its upstream LSR U for <X, Y> as per Section 3.3.
Using this Label Mapping to update the label forwarding table MUST
NOT be done as long as LSR D is equal to LSR U. If LSR U is
different from LSR D, Z will allocate a label L' and install
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RFC 7140 LDP Extensions for HSMP LSP March 2014
downstream forwarding state to swap label L' with label L over
interface I associated with LSR D and send an HSMP-D Label Mapping
<X, Y, L'> to U. Interface I is determined via the procedures in
Section 3.7.
If Z already has forwarding state for downstream <X, Y>, all that Z
needs to do in this case is check that LSR D is not equal to the
upstream LSR of <X, Y> and update its forwarding state. Assuming its
old forwarding state was L'-> {<I1, L1> <I2, L2> ..., <In, Ln>}, its
new forwarding state becomes L'-> {<I1, L1> <I2, L2> ..., <In, Ln>,
<I, L>}. If the LSR D is equal to the installed upstream LSR, the
Label Mapping from LSR D MUST be retained and MUST NOT update the
label forwarding table.
Node Z checks if the upstream LSR U already has assigned a label Lu
to upstream <X, Y>. If not, transit node Z waits until it receives
an HSMP-U Label Mapping <X, Y, Lu> from LSR U. Once the HSMP-U Label
Mapping is received from LSR U, node Z checks whether it already has
forwarding state upstream <X, Y> with incoming label Lu' and outgoing
label Lu. If it does not, it allocates a label Lu' and creates a new
label swap for Lu' with Label Lu over interface Iu. Interface Iu is
determined via the procedures in Section 3.7. Node Z determines the
downstream HSMP LSR as per Section 3.4 and sends an HSMP-U Label
Mapping <X, Y, Lu'> to node D.
Since a packet from any downstream node is forwarded only to the
upstream node, the same label (representing the upstream path) SHOULD
be distributed to all downstream nodes. This differs from the
procedures for MP2MP LSPs [RFC 6388], where a distinct label must be
distributed to each downstream node. The forwarding state upstream
<X, Y> on node Z will be like this: {<Lu'>, <Iu Lu>}. Iu means the
upstream interface over which Z receives HSMP-U Label Map <X, Y, Lu>
from LSR U. Packets from any downstream interface over which Z sends
HSMP-U Label Map <X, Y, Lu'> with label Lu' will be forwarded to Iu
with label Lu' swapped to Lu.
3.4.3. HSMP LSP Root Node Operation
The procedure for an HSMP-D Label Mapping message is much the same as
processing an MP2MP-D Label Mapping message defined in
Section 3.3.1.6 of [RFC 6388]. The processing of an HSMP-U Label
Mapping message is different from that of an MP2MP-U Label Mapping
message as specified below.
Suppose the root node Z receives an HSMP-D Label Mapping <X, Y, L>
from node D. Z checks whether it already has forwarding state for
downstream <X, Y>. If not, Z creates downstream forwarding state and
installs an outgoing label L over interface I. Interface I is
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RFC 7140 LDP Extensions for HSMP LSP March 2014
determined via the procedures in Section 3.7. If Z already has
forwarding state for downstream <X, Y>, then Z will add label L over
interface I to the existing state.
Node Z checks if it has forwarding state for upstream <X, Y>. If
not, Z creates a forwarding state for incoming label Lu' that
indicates that Z is the HSMP LSP egress Label Edge Router (LER). For
example, the forwarding state might specify that the label stack is
popped and the packet passed to some specific application. Node Z
determines the downstream HSMP LSR as per Section 3.3 and sends an
HSMP-U Label Map <X, Y, Lu'> to node D.
Since Z is the root of the tree, Z will not send an HSMP-D Label Map
and will not receive an HSMP-U Label Mapping.
The root node could also be a leaf node, and it is able to determine
what traffic to forward on this HSMP LSP; that determination is
outside the scope of this document.
3.5. HSMP LSP Label Withdraw
3.5.1. HSMP Leaf Operation
If a leaf node Z discovers that it has no need to be an Egress LSR
for that LSP (by means outside the scope of this document), then it
SHOULD send an HSMP-D Label Withdraw <X, Y, L> to its upstream LSR U
for <X, Y>, where L is the label it had previously advertised to U
for <X, Y>. Leaf node Z will also send an unsolicited HSMP-U Label
Release <X, Y, Lu> to U to indicate that the upstream path is no
longer used and that label Lu can be removed.
Leaf node Z expects the upstream router U to respond by sending a
downstream Label Release for L.
3.5.2. HSMP Transit Node Operation
If a transit node Z receives an HSMP-D Label Withdraw message
<X, Y, L> from node D, it deletes label L from its forwarding state
downstream <X, Y>. Node Z sends an HSMP-D Label Release message with
label L to D. There is no need to send an HSMP-U Label Withdraw <X,
Y, Lu> to D because node D already removed Lu and sent a label
release for Lu to Z.
If deleting L from Z's forwarding state for downstream <X, Y> results
in no state remaining for <X, Y>, then Z propagates the HSMP-D Label
Withdraw <X, Y, L> to its upstream node U for <X, Y>. Z should also
check if there are any incoming interfaces in forwarding state
upstream <X, Y>. If all downstream nodes are released and there is
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RFC 7140 LDP Extensions for HSMP LSP March 2014
no incoming interface, Z should delete the forwarding state upstream
<X, Y> and send an HSMP-U Label Release message to its upstream node.
Otherwise, no HSMP-U Label Release message will be sent to the
upstream node.
3.5.3. HSMP Root Node Operation
When the root node of an HSMP LSP receives an HSMP-D Label Withdraw
message and an HSMP-U Label Release message, the procedure is the
same as that for transit nodes, except that the root node will not
propagate the Label Withdraw and Label Release upstream (as it has no
upstream).
3.6. HSMP LSP Upstream LSR Change
The procedure for changing the upstream LSR is the same as defined in
Section 2.4.3 of [RFC 6388], only with different processing of the FEC
Element.
When the upstream LSR changes from U to U', node Z should set up the
HSMP LSP <X, Y> to U' by applying the procedures in Section 3.4. Z
will also remove the HSMP LSP <X, Y> to U by applying the procedure
in Section 3.5.
To set up an HSMP LSP to U' before/after removing the HSMP LSP to U
is a local matter. The recommended default behavior is to remove
before adding.
3.7. Determining Forwarding Interface
The upstream and downstream LSPs can be co-routed by applying the
procedures below. Both LSR U and LSR D would ensure that the same
interface sends traffic by applying some procedures. For a network
with symmetric IGP cost configuration, the following procedure MAY be
used. To determine the downstream interface, LSR U MUST do a lookup
in the unicast routing table to find the best interface and next hop
to reach LSR D. If the next hop and interface are also advertised by
LSR D via the LDP session, it should be used to transmit the packet
to LSR D. The mechanism to determine the upstream interface is the
same as that used to determine the downstream interface except the
roles of LSR U and LSR D are switched. If symmetric IGP cost could
not be ensured, static route configuration on LSR U and D could also
be a way to ensure a co-routed path.
If a co-routed path is not required for the HSMP LSP, the procedure
defined in Section 2.4.1.2 of [RFC 6388] could be applied. LSR U is
free to transmit the packet on any of the interfaces to LSR D. The
algorithm it uses to choose a particular interface is a local matter.
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The mechanism to determine the upstream interface is the same as that
used to determine the downstream interface.
4. HSMP LSP on a LAN
The procedure to process the downstream HSMP LSP on a LAN is much the
same as for a downstream MP2MP LSP as described in Section 6.1.1 of
[RFC 6388].
When establishing the downstream path of an HSMP LSP, as defined in
[RFC 6389], a Label Request message for an LSP label is sent to the
upstream LSR. The upstream LSR should send a Label Mapping message
that contains the LSP label for the downstream HSMP FEC and the
upstream LSR context label defined in [RFC 5331]. When the LSR
forwards a packet downstream on one of those LSPs, the packet's top
label must be the "upstream LSR context label" and the packet's
second label is the "LSP label". The HSMP downstream path will be
installed in the context-specific forwarding table corresponding to
the upstream LSR label. Packets sent by the upstream LSR can be
forwarded downstream using this forwarding state based on a two-label
lookup.
The upstream path of an HSMP LSP on a LAN is the same as the one on
other kinds of links. That is, the upstream LSR must send a Label
Mapping message that contains the LSP label for the upstream HSMP FEC
to the downstream node. Packets traveling upstream need to be
forwarded in the direction of the root by using the label allocated
for the upstream HSMP FEC.
5. Redundancy Considerations
In some scenarios, it is necessary to provide two root nodes for
redundancy purposes. One way to implement this is to use two
independent HSMP LSPs acting as active and standby. At a given time,
only one HSMP LSP will be active; the other will be standby. After
detecting the failure of the active HSMP LSP, the root and leaf nodes
will switch the traffic to the standby HSMP LSP, which takes on the
role as active HSMP LSP. The details of the redundancy mechanism are
out of the scope of this document.
6. Failure Detection of HSMP LSP
The idea of LSP ping for HSMP LSPs could be expressed as an intention
to test the LSP Ping Echo Request packets that enter at the root
along a particular downstream path of HSMP LSP and that end their
MPLS path on the leaf. The leaf node then sends the LSP Ping Echo
Reply along the upstream path of HSMP LSP, and it ends on the root
that is the (intended) root node.
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New sub-TLVs have been assigned by IANA in Target FEC Stack TLV and
Reverse-path Target FEC Stack TLV to define the corresponding HSMP-
downstream FEC type and HSMP-upstream FEC type. In order to ensure
that the leaf node sends the LSP Ping Echo Reply along the HSMP
upstream path, the R flag (Validate Reverse Path) in the Global Flags
field defined in [RFC 6426] is reused here.
The node-processing mechanism of LSP Ping Echo Request and Echo Reply
for the HSMP LSP is inherited from [RFC 6425] and Section 3.4 of
[RFC 6426], except for the following:
1. The root node sending the LSP Ping Echo Request message for the
HSMP LSP MUST attach the Target FEC Stack TLV with the HSMP-
downstream FEC type, and set the R flag to '1' in the Global
Flags field.
2. When the leaf node receives the LSP Ping Echo Request, it MUST
send the LSP Ping Echo Reply to the associated HSMP upstream
path. The Reverse-path Target FEC Stack TLV attached by the leaf
node in the Echo Reply message SHOULD contain the sub-TLV of the
associated HSMP-upstream FEC.
7. Security Considerations
The same security considerations apply as for the MP2MP LSP described
in [RFC 6388] and [RFC 6425].
Although this document introduces new FEC Elements and corresponding
procedures, the protocol does not bring any new security issues
beyond those in [RFC 6388] and [RFC 6425].
8. IANA Considerations
8.1. New LDP FEC Element Types
Two new LDP FEC Element types have been allocated from the "Label
Distribution Protocol (LDP) Parameters" registry, under "Forwarding
Equivalence Class (FEC) Type Name Space":
1. the HSMP-upstream FEC type - 9
2. the HSMP-downstream FEC type - 10
The values have been allocated from the "IETF Consensus" [RFC 5226]
range (0-127).
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RFC 7140 LDP Extensions for HSMP LSP March 2014
8.2. HSMP LSP Capability TLV
One new code point has been allocated for the HSMP LSP capability TLV
from "Label Distribution Protocol (LDP) Parameters" registry, under
"TLV Type Name Space":
HSMP LSP Capability Parameter - 0x0902
The value has been allocated from the"IETF Consensus" range
(0x0901-0x3DFF).
8.3. New Sub-TLVs for the Target Stack TLV
Two new sub-TLV types have been allocated for inclusion within the
LSP ping [RFC 4379] Target FEC Stack TLV (TLV type 1), Reverse-path
Target FEC Stack TLV (TLV type 16), and Reply Path TLV (TLV type 21).
o the HSMP-upstream LDP FEC Stack - 29
o the HSMP-downstream LDP FEC Stack - 30
The value has been allocated from the "IETF Standards Action" range
(0-16383) that is used for mandatory and optional sub-TLVs that
requires a response if not understood.
9. Acknowledgements
The author would like to thank Eric Rosen, Sebastien Jobert, Fei Su,
Edward, Mach Chen, Thomas Morin, and Loa Andersson for their valuable
comments.
Jin, et al. Standards Track PAGE 13
RFC 7140 LDP Extensions for HSMP LSP March 2014
10. References
10.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space", RFC
5331, August 2008.
[RFC 5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
Multicast Encapsulations", RFC 5332, August 2008.
[RFC 5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
Le Roux, "LDP Capabilities", RFC 5561, July 2009.
[RFC 6388] 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.
[RFC 6389] Aggarwal, R. and JL. Le Roux, "MPLS Upstream Label
Assignment for LDP", RFC 6389, November 2011.
[RFC 6425] Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,
S., and T. Nadeau, "Detecting Data-Plane Failures in
Point-to-Multipoint MPLS - Extensions to LSP Ping", RFC
6425, November 2011.
[RFC 6426] Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
On-Demand Connectivity Verification and Route Tracing",
RFC 6426, November 2011.
10.2. Informative References
[RFC 4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[RFC 5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC 5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Jin, et al. Standards Track PAGE 14
RFC 7140 LDP Extensions for HSMP LSP March 2014
Authors' Addresses
Lizhong Jin
Shanghai
China
EMail: lizho.jin@gmail.com
Frederic Jounay
Orange CH
4 rue du Caudray
1007 Lausanne
Switzerland
EMail: frederic.jounay@orange.ch
IJsbrand Wijnands
Cisco Systems, Inc
De kleetlaan 6a
Diegem 1831
Belgium
EMail: ice@cisco.com
Nicolai Leymann
Deutsche Telekom AG
Winterfeldtstrasse 21
Berlin 10781
Germany
EMail: N.Leymann@telekom.de
Jin, et al. Standards Track PAGE 15
RFC TOTAL SIZE: 33570 bytes
PUBLICATION DATE: Sunday, March 2nd, 2014
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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