Internet DRAFT - draft-jjwl-mpls-mldp-hsmp
draft-jjwl-mpls-mldp-hsmp
Network Working Group L. Jin
Internet-Draft ZTE Corporation
Intended status: Standards Track F. Jounay
Expires: March 7, 2013 France Telecom
I. Wijnands
Cisco Systems, Inc
N. Leymann
Deutsche Telekom AG
Sep 3, 2012
LDP Extensions for Hub & Spoke Multipoint Label Switched Path
draft-jjwl-mpls-mldp-hsmp-01.txt
Abstract
This draft introduces a hub & spoke multipoint LSP (short for HSMP
LSP), which allows traffic both from root to leaf through P2MP LSP
and also leaf to root along the co-routed reverse path. That means
traffic entering the HSMP LSP from application/customer at the root
node travels downstream, exactly as if it was traveling downstream
along a P2MP LSP to each leaf node, and traffic entering the HSMP LSP
at any leaf node travels upstream along the tree to the root as if it
is unicast to the root, except that it follows the path of the tree
rather than ordinary unicast to the root.
Requirements 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 RFC2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 7, 2013.
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Copyright Notice
Copyright (c) 2012 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Time synchronization scenario . . . . . . . . . . . . . . 4
3.2. VPMS scenario . . . . . . . . . . . . . . . . . . . . . . 4
3.3. IPTV scenario . . . . . . . . . . . . . . . . . . . . . . 4
4. Setting up HSMP LSP with LDP . . . . . . . . . . . . . . . . . 5
4.1. Support for HSMP LSP setup with LDP . . . . . . . . . . . 5
4.2. HSMP FEC Elements . . . . . . . . . . . . . . . . . . . . 6
4.3. Using the HSMP FEC Elements . . . . . . . . . . . . . . . 6
4.3.1. HSMP LSP Label Map . . . . . . . . . . . . . . . . . . 6
4.3.2. HSMP LSP Label Withdraw . . . . . . . . . . . . . . . 8
4.3.3. HSMP LSP upstream LSR change . . . . . . . . . . . . . 9
5. HSMP LSP on a LAN . . . . . . . . . . . . . . . . . . . . . . 9
6. Redundancy considerations . . . . . . . . . . . . . . . . . . 9
7. Co-routed path exceptions . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative references . . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
The point-to-multipoint LSP defined in [RFC6388] allows traffic to
transmit from root to several leaf nodes, and multipoint-to-
multipoint LSP allows traffic from every node to transmit to every
other node. This draft introduces a hub & spoke multipoint LSP
(short for HSMP LSP), which allows traffic both from root to leaf
through P2MP LSP and also leaf to root along the co-routed reverse
path. That means traffic entering the HSMP LSP at the root node
travels downstream, exactly as if it was traveling downstream along a
P2MP LSP, and traffic entering the HSMP LSP at any other node travels
upstream along the tree to the root. A packet traveling upstream
should be thought of as being unicast to the root, except that it
follows the path of the tree rather than ordinary unicast to the
root.
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 [RFC2119].
This document uses some terms and acronyms as follows:
mLDP: Multipoint extensions for LDP
P2MP LSP: An LSP that has one Ingress LSR and one or more Egress
LSRs.
MP2MP LSP: 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 & spoke multipoint LSP. An LSP allows traffic both
from root to leaf through P2MP LSP and also leaf to root along the
co-routed reverse path.
PTP: The timing and synchronization protocol used by IEEE1588
3. Applications
In some cases, the P2MP LSP may not have a reply path for the OAM
message (e.g, LSP Ping). If P2MP LSP is provided by HSMP LSP, then
the upstream path could be exactly used as the OAM message reply
path. This is especially useful in the case of P2MP LSP fault
detection, performance measurement, root node redundancy and etc.
There are several other applications that could take advantage of
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such kind of LDP based HSMP LSP as described below.
3.1. Time synchronization scenario
[IEEE1588] over MPLS is defined in [I-D.ietf-tictoc-1588overmpls].
It is required that the LSP used to transport PTP event message
between a Master Clock and a Slave Clock, and the LSP between the
same Slave Clock and Master Clock must be co-routed. By using point-
to-multipoint technology to transmit PTP event messages from Master
Clock at root side to Slave Clock at leaf side will greatly improve
the bandwidth usage. Unfortunately current point-to-multipoint LSP
only provides unidirectional path from root to leaf, which cannot
provide a co-routed reverse path for the PTP event messages. LDP
based HSMP LSP described in this draft provides unidirectional point-
to-multipoint LSP from root to leaf and co-routed reverse path from
leaf to root.
3.2. VPMS scenario
Point to multipoint PW described in [I-D.ietf-pwe3-p2mp-pw] requires
to setup reverse path from leaf node (referred as egress PE) to root
node (referred as ingress PE), if HSMP LSP is used to multiplex P2MP
PW, the reverse path can also be multiplexed to HSMP upstream path to
avoid setup independent reverse path. In that case, the operational
cost will be reduced for maintaining only one HSMP LSP, instead of
P2MP LSP and n (number of leaf nodes) P2P reverse LSPs.
The VPMS defined in [I-D.ietf-l2vpn-vpms-frmwk-requirements] requires
reverse path from leaf to root node. The P2MP PW multiplexed to HSMP
LSP can provide VPMS with reverse path, without introducing
independent reverse path from each leaf to root.
3.3. IPTV scenario
The mLDP based HSMP LSP can also be applied in a typical IPTV
scenario. There is usually only one location with senders but there
are many receiver locations. If IGMP is used for signaling between
senders as IGMP querier and receivers, the IGMP messages from the
receivers are travelling only from the leaves to the root (and from
root towards leaves) but not from leaf to leaf. In addition traffic
from the root is only replicated towards the leaves. Then leaf node
receiving IGMP message (for SSM case) will join HSMP LSP, and then
send IGMP message upstream to root along HSMP LSP. Note that in
above case, there is no node redundancy for IGMP querier. And the
node redundancy for IGMP querier could be provided by two independent
VPMS instances with HSMP applied.
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4. Setting up HSMP LSP with LDP
HSMP LSP is similar with MP2MP LSP described in [RFC6388], with the
difference that the leaf LSRs can only send traffic to root node
along the same path of traffic from root node to leaf node.
HSMP LSP consists of a downstream path and upstream path. The
downstream path is same as MP2MP LSP, while the upstream path is only
from leaf to root node, without communication between leaf and leaf
nodes. The transmission of packets from the root node of a HSMP LSP
to the receivers is identical to that of a P2MP LSP. Traffic from a
leaf node follows the upstream path toward the root node, along the
identical path of downstream path.
For setting up the upstream path of a HSMP LSP, ordered mode MUST be
used which is same as MP2MP. Ordered mode can guarantee a leaf to
start sending packets to root immediately after the upstream path is
installed, without being dropped due to an incomplete LSP.
Due to much of same behavior between HSMP LSP and MP2MP LSP, the
following sections only describe the difference between the two
entities.
4.1. Support for HSMP LSP setup with LDP
HSMP LSP also needs the LDP capabilities [RFC5561] to indicate the
supporting for the 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.
Following 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| HSMP LSP Cap(TBD IANA) | Length (= 1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Reserved |
+-+-+-+-+-+-+-+-+
Figure 1. HSMP LSP Capability Parameter encoding
The HSMP LSP capability type is to be assigned by IANA.
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4.2. HSMP FEC Elements
Similar as MP2MP LSP, we define two new protocol entities, the HSMP
downstream FEC and upstream FEC Element. If a FEC TLV contains an
HSMP FEC Element, the HSMP FEC Element MUST be the only FEC Element
in the FEC TLV. The structure, encoding and error handling for the
HSMP downstream and upstream FEC Elements are the same as for the
MP2MP FEC Element described in [RFC6388] Section 4.2. The difference
is that two additional new FEC types are used: HSMP downstream type
(TBD, IANA) and HSMP upstream type (TBD, IANA).
4.3. Using the HSMP FEC Elements
In order to describe the message processing clearly, following
defines the processing of the HSMP FEC Elements, which is inherited
from [RFC6388] section 4.3.
1. HSMP downstream LSP <X, Y> (or simply downstream <X, Y>): a HSMP
LSP downstream path with root node address X and opaque value Y.
2. HSMP upstream LSP <X, Y> (or simply upstream <X, Y>): a HSMP LSP
upstream path for root node address X and opaque value Y which will
be used by any of 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 Map <X, Y, L>: A Label Map 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 Map Message.
6. HSMP-U Label Map <X, Y, Lu>: A Label Map 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 Map Message.
4.3.1. HSMP LSP Label Map
This section specifies the procedures for originating HSMP Label Map
messages and processing received HSMP label map messages for a
particular HSMP LSP. The procedure of downstream HSMP LSP is same as
that of downstream MP2MP LSP described in [RFC6388]. Under the
operation of ordered mode, the upstream LSP will be setup by sending
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HSMP LSP mapping message with label which is allocated by upstream
LSR to its downstream LSR one by one from root to leaf node,
installing the upstream forwarding table by every node along the LSP.
Detail procedure of upstream HSMP LSP is different with that of
upstream MP2MP LSP, and is specified in below section.
All labels discussed here are downstream-assigned [RFC5332] except
those which are assigned using the procedures described in section 5.
Determining the upstream LSR for a HSMP LSP <X, Y> follows the
procedure for a MP2MP LSP described in [RFC6388] Section 4.3.1.1.
Determining one's downstream HSMP LSR procedure is much same as
defined in [RFC6388] section 4.3.1.2. A LDP peer U which receives a
HSMP-D Label Map from a LDP peer D will treat D as downstream HSMP
LSR.
Determining the forwarding interface to an LSR has same procedure as
defined in [RFC6388] section 2.4.1.2.
4.3.1.1. HSMP LSP leaf node operation
The leaf node operation is same as the operation of MP2MP LSP defined
in [RFC6388] section 4.3.1.4, only with different FEC element
processing and specified below.
A leaf node Z will send a HSMP-D Label Map <X, Y, L> to U, instead of
MP2MP-D Label Map <X, Y, L>. and expects a HSMP-U Label Map <X, Y,
Lu> from node U and checks whether it already has forwarding state
for upstream <X, Y>. The created forwarding state on leaf node Z is
same as the leaf node of MP2MP LSP. Z will push label Lu onto the
traffic that Z wants to forward over the HSMP LSP.
4.3.1.2. HSMP LSP transit node operation
Suppose node Z receives a HSMP-D Label Map <X, Y, L> from LSR D, the
procedure is same as processing MP2MP-D Label Mapping message defined
in [RFC6388] section 4.3.1.5, and the processing protocol entity is
HSMP-D label mapping message. The different procedure is specified
below.
Node Z checks if upstream LSR U already assigned a label Lu to
upstream <X, Y>. If not, transit node Z waits until it receives a
HSMP-U Label Map <X, Y, Lu> from LSR U. Once the HSMP-U Label Map 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, Z sends a HSMP-U Label Map <X, Y, Lu'> to downstream
node. If it does not, it allocates a label Lu' and creates a new
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label swap for Lu' with Label Lu over interface Iu. Interface Iu is
determined via the procedures in Section 4.3.1. Node Z determines
the downstream HSMP LSR as per Section 4.3.1, and sends a HSMP-U
Label Map <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) can be
distributed to all downstream nodes. This differs from the
procedures for MPMP LSPs [RFC6388], 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 send
HSMP-U Label Map <X, Y, Lu'> with label Lu' will be forwarded to Iu
with label Lu' swap to Lu.
4.3.1.3. HSMP LSP root node operation
Suppose root node Z receives a HSMP-D Label Map <X, Y, L> from node
D, the procedure is much same as processing MP2MP-D Label Mapping
message defined in [RFC6388] section 4.3.1.6, and the processing
protocol entity is HSMP-D label mapping message. The different
procedure is specified below.
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 LSP egress. E.g., 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 4.3.1, and sends a HSMP-U Label Map <X, Y, Lu'> to node
D.
Since Z is the root of the tree, Z will not send a HSMP-D Label Map
and will not receive a HSMP-U Label Map.
4.3.2. HSMP LSP Label Withdraw
The HSMP Label Withdraw procedure is much same as MP2MP leaf
operation defined in [RFC6388] section 4.3.2, and the processing
protocol entities are HSMP FECs. The only difference is process of
HSMP-U label release message, which is specified below.
When a transit node Z receives a HSMP-U label release message from
downstream node D, Z should check if there are any incoming interface
in forwarding state upstream <X, Y>. If all downstream nodes are
released and there is no incoming interface, Z should delete the
forwarding state upstream <X, Y> and send HSMP-U label release
message to its upstream node.
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4.3.3. HSMP LSP upstream LSR change
The procedure for changing the upstream LSR is the same as defined in
[RFC6388] section 4.3.3, except it is applied to HSMP FECs.
5. HSMP LSP on a LAN
The procedure to process P2MP LSP on a LAN has been described in
[RFC6388]. When the LSR forwards a packet downstream on one of those
LSPs, the packet's top label must be the "upstream LSR label", and
the packet's second label is "LSP label".
When establishing the downstream path of a HSMP LSP, as defined in
[RFC6389], a label request for a LSP label is send to the upstream
LSR. The upstream LSR should send label mapping that contains the
LSP label for the downstream HSMP FEC and the upstream LSR context
label. At the same time, it must also send label mapping for
upstream HSMP FEC to downstream node. Packets sent by the upstream
router can be forwarded downstream using this forwarding state based
on a two label lookup. Packets traveling upstream need to be
forwarded in the direction of the root by using the label allocated
by upstream LSR.
6. Redundancy considerations
In some scenario, it is necessary to provide two root nodes for
redundancy purpose. One way to implement this is to use two
independent HSMP LSPs acting as active/standby. At one time, only
one HSMP LSP will be active, and the other will be standby. After
detecting the failure of active HSMP LSP, the root and leaf nodes
will switch the traffic to the new active HSMP LSP which is switched
from former standby LSP. The detail of redundancy mechanism will be
for future study.
7. Co-routed path exceptions
There are some exceptional cases that mLDP based HSMP LSP could not
achieve co-routed path. One possible case is using static routing
between LDP neighbors; another possible case is IGP cost asymmetric
generated by physical link cost asymmetric, or TE-Tunnels used
between LDP neighbors. The LSR/LER in HSMP LSP could detect if the
path is co-routed or not, if not co-routed, an indication could be
generated to the management system.
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8. Security Considerations
The same security considerations apply as for the MP2MP LSP described
in [RFC6388].
9. IANA Considerations
This document requires allocation of two new LDP FEC Element types
from the "Label Distribution Protocol (LDP) Parameters registry" the
"Forwarding Equivalence Class (FEC) Type Name Space":
1. the HSMP-upstream FEC type - requested value TBD
2. the HSMP-downstream FEC type - requested value TBD
This document requires allocation of one new code points for the HSMP
LSP capability TLV from "Label Distribution Protocol (LDP) Parameters
registry" the "TLV Type Name Space":
HSMP LSP Capability Parameter - requested value TBD
10. Acknowledgement
The author would like to thank Eric Rosen, Sebastien Jobert, Fei Su,
Edward, Mach Chen, Thomas Morin for their valuable comments.
11. References
11.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
Multicast Encapsulations", RFC 5332, August 2008.
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
Le Roux, "LDP Capabilities", RFC 5561, July 2009.
[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.
[RFC6389] Aggarwal, R. and JL. Le Roux, "MPLS Upstream Label
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Assignment for LDP", RFC 6389, November 2011.
11.2. Informative References
[I-D.ietf-l2vpn-vpms-frmwk-requirements]
Kamite, Y., JOUNAY, F., Niven-Jenkins, B., Brungard, D.,
and L. Jin, "Framework and Requirements for Virtual
Private Multicast Service (VPMS)",
draft-ietf-l2vpn-vpms-frmwk-requirements-04 (work in
progress), July 2011.
[I-D.ietf-pwe3-p2mp-pw]
Sivabalan, S., Boutros, S., and L. Martini, "Signaling
Root-Initiated Point-to-Multipoint Pseudowire using LDP",
draft-ietf-pwe3-p2mp-pw-04 (work in progress), March 2012.
[I-D.ietf-tictoc-1588overmpls]
Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
Montini, "Transporting PTP messages (1588) over MPLS
Networks", draft-ietf-tictoc-1588overmpls-02 (work in
progress), October 2011.
[IEEE1588]
"IEEE standard for a precision clock synchronization
protocol for networked measurement and control systems",
IEEE1588v2 , March 2008.
[RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
Authors' Addresses
Lizhong Jin
ZTE Corporation
889, Bibo Road
Shanghai, 201203, China
Email: lizhong.jin@zte.com.cn
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Frederic Jounay
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex, FRANCE
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
Email: N.Leymann@telekom.de
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