Network Working Group N. So
Internet Draft A. Malis
Intended Status: Informational D. McDysan
Expires: December 2011 Verizon
L. Yong
Huawei
C. Villamizar
Infinera
T. Li
Cisco
June 9, 2011
Composite Link Framework in Multi Protocol Label Switching (MPLS)
draft-so-yong-rtgwg-cl-framework-04
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79. This document may not be
modified, and derivative works of it may not be created, and it may
not be published except as an Internet-Draft.
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79. This document may not be
modified, and derivative works of it may not be created, except to
publish it as an RFC and to translate it into languages other than
English.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
So, et al. Expires December 2011 [Page 1]
Internet-Draft Composite Link Framework June 2011
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on December 9, 2011.
Copyright Notice
Copyright (c) 2011 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.
Abstract
This document specifies a composite link framework in MPLS network.
A composite link consists of a group of homogenous or non-homogenous
links that have the same forward adjacency and can be considered as
a single TE link or an IP link in routing. A composite link relies
on its component links to carry the traffic over the composite link.
The document specifies composite link framework. Applicability is
described for a single pair of MPLS-capable nodes, a sequence of
MPLS-capable nodes, or a set of layer networks connecting MPLS-
capable nodes.
Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................3
2.1. Terminology...............................................3
3. Composite Link Framework.......................................4
4. Composite Link in Control Plane................................6
5. Composite Link in Data Plane...................................8
6. Composite Link in Management Plane.............................9
7. Security Considerations........................................9
8. IANA Considerations............................................9
9. References.....................................................9
9.1. Normative References......................................9
9.2. Informative References...................................10
10. Acknowledgments..............................................10
So, et al. Expires December 2011 [Page 2]
Internet-Draft Composite Link Framework June 2011
1. Introduction
Composite link functional requirements are specified in [CL-REQ].
This document specifies a framework of Composite Link in MPLS
network to meet the requirements. Single link and LAG based link
bundle have been widely used in today's MPLS networks. A link bundle
[RFC4201] bundles a group of homogeneous links as a TE link to make
routing approach more scalable. A composite link allows bundling
non-homogenous links together as a single logical link. The
motivations for using a composite link are descried in the document
[CL-REQ]. This document describes composite link framework in the
context of MPLS network with MPLS control plane.
A composite link is a single logical link in MPLS network that
contains multiple parallel component links between two routers.
Unlike a link bundle [RFC4201], the component links in a composite
link can have different properties such as cost or capacity. A
composite link can transport aggregated traffic as other physical
links from the network perspective and use its component links to
carry the traffic internally.
Specific protocol solutions are outside the scope of this document.
2. Conventions used in this document
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].
2.1. Terminology
Composite Link: A composite link is a logical link composed of a
set of parallel point-to-point component links, where all links in
the set share the same endpoints. A composite link may itself be a
component of another composite link, but only a strict hierarchy of
links is allowed.
Component Link: A point-to-point physical or logical link that
preserves ordering in the steady state. A component link may have
transient out of order events, but such events must not exceed the
network's specific NPO. Examples of a physical link are: Lambda,
Ethernet PHY, and OTN. Examples of a logical link are: MPLS LSP,
Ethernet VLAN, and MPLS-TP LSP.
Flow: A sequence of packets that must be transferred in order on
one component link.
So, et al. Expires December 2011 [Page 3]
Internet-Draft Composite Link Framework June 2011
Flow identification: The label stack and other information that
uniquely identifies a flow. Other information in flow
identification may include an IP header, PW control word, Ethernet
MAC address, etc. Note that an LSP may contain one or more Flows or
an LSP may be equivalent to a Flow. Flow identification is used to
locally select a component link, or a path through the network
toward the destination.
Network Performance Objective (NPO): Numerical values for
performance measures, principally availability, latency, and delay
variation. See Appendix A for more details.
3. Composite Link Framework
A Composite Link in the context of MPLS network is a set of parallel
links between two routers that form a single logical link within the
network. Composite link model is illustrated in Figure 1, where a
composite link is configured between routers R1 and R2. The
composite link has three component links. Individual component
links in a composite link may be supported by different transport
technologies such as wavelength, Ethernet VLAN. Even if the
transport technology implementing the component links is identical,
the characteristics (e.g., bandwidth, latency) of the component
links may differ.
As shown in Figure 1, the composite link may carry LSP traffic flows
and control plane packets that appear as IP packets. A LSP may be
established over the link by either RSVP-TE or LDP signaling
protocols. All component links in a composite link have the same
forwarding adjacency. The composite link forms one routing interface
at the composite link end points for MPLS control plane. In other
words, two routers connected via a composite link have forwarding
adjacency and routing adjacency. Each component link only has
significance to the composite link, i.e. it does not appear as a
link in the control plane.
So, et al. Expires December 2011 [Page 4]
Internet-Draft Composite Link Framework June 2011
Management Plane
Configuration and Measurement <------------+
^ |
| |
+-------+-+ +-+-------+
| | | | | |
CP Packets V | | V CP Packets
| V | | Component Link 1 | | ^ |
| | |=|===========================|=| | |
| +----| | Component Link 2 | |----+ |
| |=|===========================|=| |
Aggregated LSPs | | | | |
~|~~~~~~>| | Component Link 3 | |~~~~>~~|~~
| |=|===========================|=| |
| | | | | |
| LSR | | LSR |
+---------+ +---------+
! !
! !
!<------ Composite Link ------->!
Figure 1 Composite Link Architecture Model
A component link in a composite link may be constructed in different
ways.[CL-REQ] Figure 2 shows three common ways that may be deployed
in a network.
+-------+ 1. Physical Link +-------+
| |-|----------------------------------------------|-| |
| | | | | |
| | | +------+ +------+ | | |
| | | | MPLS | 2. Logical Link | MPLS | | | |
| |.|.... |......|.....................|......|....|.| |
| | |-----| R3 |---------------------| R4 |----| | |
| | | +------+ +------+ | | |
| | | | | |
| | | | | |
| | | +------+ +------+ | | |
| | | |GMPLS | 3. Logical Link |GMPLS | | | |
| |.|. ...|......|.....................|......|....|.| |
| | |-----| R5 |---------------------| R6 |----| | |
| | +------+ +------+ | |
| R1 | | R2 |
+-------+ +-------+
|<------------- Composite Link ------------------->|
Figure 2 Illustration of Component Link Variances
So, et al. Expires December 2011 [Page 5]
Internet-Draft Composite Link Framework June 2011
As shown, the first component link is configured with direct
physical media wire. The second component link is a TE tunnel that
traverses R3 and R4. Both R3 and R4 are the nodes in the MPLS. The
third component link is formed by lower layer network that has GMPLS
enabled. In this case, R5 and R6 are not the nodes controlled by the
MPLS but provide the connectivity for the component link. Note: if
two unidirectional LSPs are used to construct a component link, they
MUST be co-routed.
Composite link forms one logical link between connected routers and
is used to carry aggregated traffic.[CL-REQ] Composite link relies
on its component links to carry the traffic over the composite link.
This means that a composite link maps incoming traffic into
component links. The router (R1 in Figure 1) of composite link
ingress maps a set of traffic flows including control plane packets
to a specific component link. The router (R2 in Figure 1) of
composite link egress receives the packets from its component links
and sends them to MPLS forwarding engine like a regular link. The
traffic from R2 to R1 is distributed by the router R2.
Traffic mapping to component links may be done by control plane,
management plane, or data plane.[CL-REQ] The objectives are to keep
the individual flow packets in sequence and meet its QoS criteria,
do not overload any component link, and be able to perform local
recovery when one of component link fails.[CL-REQ] Operator may have
other objectives such as placing a bi-directional flow or LSP on the
same component link in both direction, load balance over component
links, composite link energy saving, and etc. A flow may be a LSP,
or sub-LSP [MLSP], PW, a flow within PW [FAT-PW], entropy flow in
LSP [ENTROPY].
4. Composite Link in Control Plane
A composite Link is advertised as a single logical interface between
two connected routers, which forms routing and forwarding adjacency
between the routers in IGP. The interface parameters for the
composite link can be pre-configured by operator or be derived from
its component links. Composite link advertisement requirements are
specified in [CL-REQ].
In IGP-TE, a composite link is advertised as a single TE link
between two connected routers. This is similar to a link bundle
[RFC4201]. Link bundle applies to a set of homogenous component
links. Composite link allows homogenous and non-homogenous component
links. In order for route computing engine to calculate a proper
path for a LSP, it is necessary for composite link to advertise the
summarized available BW as well as the maximum BW for single LSP. If
a composite link contains some non-homogeneous component links, the
composite link also need to advertise the summarized BW and the
maximum BW for single LSP per each homogeneous component link group.
The protocol extension for composite link advertisement will be
described in the separated draft.
So, et al. Expires December 2011 [Page 6]
Internet-Draft Composite Link Framework June 2011
Current IGP Link announcement protocol does not give such
capability. The protocol only allows advertising one cost based TE
metrics. RFC4201 only advertises a largest available BW for a link
bundle that includes a set of homogenous component links. Signaling
protocol does not allow signaling an aggregated LSP where its BW may
be larger than the capacity of any component links. [ENTROPY]
A composite link may contain the set of component links. A component
link may be configured by operator or signaled by the control plane.
If two unidirectional LSPs are used to construct a component link,
they MUST be co-routed. In both cases, it is necessary to convey
component link parameters to the composite link.[CL-REQ] In an often
case, a component link is configured to carry traffic under normal
operation; under some situation, operator may want to configure a
component link as a link for local recovery purpose, in which the
composite link should not count the component link TE parameters
into the composite link TE parameters for the advertisement. However,
the composite link may send the traffic over the component link when
a component link failure occurs. The protocol extension for singling
component link parameter is for further study. This capability is
not supported in current protocol because a link bundle contains a
set of homogenous links.
When a component link is supported by lower layer network (third
component link in figure 2), the control plane that the composite
link resides is able to interoperate with the GMPLS or MPLS-TP
control plane that lower layer network uses for component link
addition and deletion.[CL-REQ]
It is possible for operator to configure one or multiple interface
(s) over a composite link.
Both LDP [RFC5036] and RSVP-TE [RFC3209] can be used to signal a LSP
over a composite link. The router of composite link ingress MUST
place the LSP on the component link that meets the LSP criteria
indicated in the signaling message. Since the composite link brings
some unique characteristics, some signaling protocol extensions are
expected to facilitate the composite link to place LSP to a proper
component link. Several cases may be considered as below. Signaling
extension for configuring such LSP is for further study.
A composite link may contain non-homogeneous component links. The
route computing engine may select one group of component links for a
LSP, it is necessary for signaling protocol to be able to indicate
which group of component links for signaled LSP. Composite link MUST
place the LSP to the component link whose performance such as delay
or jitter is equal or better than the required.
Since composite link capacity is aggregated capacity and is larger
than individual component link capacity, it is possible to signal a
LSP whose BW is larger than individual component link capacity.[CL-
REQ] Assumption is such LSP carrying an aggregated traffic.
So, et al. Expires December 2011 [Page 7]
Internet-Draft Composite Link Framework June 2011
When a bi-directional LSP request is signaled over a composite link,
if the request indicates that the LSP must be placed on the same
component link, the routers of the composite link MUST place the LSP
traffic in both directions on a same component link.
Individual component link may fail independently. Upon component
link failure, a composite link needs to perform local recovery, i.e.
use some available capacity in other component link to carry
impacted traffic. Composite link may use LDP or RSVP-TE signaling
protocol to facilitate the recovery process between two routers that
composite resides. To avoid looped crankback, during the local
recovery process, the composite link should advertise its available
BW as zero; after finishing the local recovery, it should update its
proper available BW in IGP.
5. Composite Link in Data Plane
The traffic over a composite link is distributed over individual
component links. Traffic dissemination may be determined by control
plane, management plane, or data plane, and may be changed due to
component link status change.[CL-REQ] The distribution function is
local to the routers in which a composite link belongs to and is not
specified here. However, if a bi-directional LSP is required to be
placed on the same component link in both directions, the routers at
both composite link end points need incorporation in determining the
component link for the LSP. The protocol extension of that is for
further study.
When performing traffic placement, a composite link does not
differentiate multicast traffic vs. unicast traffic.
A component link in a composite link may fail independently. The
routers at a composite link MUST maintain each component link
status. Two routers may use the control plane to sync up a component
link state. When a component link fails, the routers of a composite
link MUST re-assign impacted flows to other active component links
in minimal disruptive manner. This is local function and do not
incorporate with LSP head-end routers. When a composite link is not
able to transport all flows, it preempts some flows based upon local
management configuration and informs the control plane on these
preempted flows. The composite link MUST support soft preemption
[RFC5712]. This action ensures the remaining traffic is transported
properly. Note: as mentioned in section 4, in order to prevent
lopped crankback symptom, when composite link performs local
recovery process, it should advertise its available BW as zero; when
the local process completes, the composite link should update its
link state with the proper available BW.
The composite link functions provide component link fault
notification and composite link fault notification. Component link
fault notification MUST be sent to the management plane. Composite
So, et al. Expires December 2011 [Page 8]
Internet-Draft Composite Link Framework June 2011
link fault notification MUST be sent to management plane and
distribute via link state message in IGP.
Operator may want to perform an optimization function such as load
balance or energy saving over a composite link, which may conduct
some traffic moving from one component link to another. The process
MUST support locally and gracefully traffic movement process among
component links. The protocol that facilitates this process between
two composite link end points is for further study.
6. Composite Link in Management Plane
Management Plane MUST keep tracking a composite link and its
individual composite link status and configuration. Management Plane
MUST be able to make any component link in a composite link active
and de-activate in order to facilitate operation maintenance task.
The routers of a composite link resides MUST perform the
redistribution of the traffic flows on a de-activated link to other
component links based on the traffic flow TE criteria.
Management Plane MUST be able to configure a LSP over a composite
link and be able to select a component link for the LSP.
Management Plane MUST be able to trace which component link a LSP is
assigned to and monitor individual component link and composite link
performance.
Management Plane MUST be able to ping individual component link
within a composite link.
Management Plane should build the proper commands to allow operator
execute an optimization process.
7. Security Considerations
For further study.
8. IANA Considerations
IANA actions to provide solutions are for further study.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G.
Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels," December
2001
So, et al. Expires December 2011 [Page 9]
Internet-Draft Composite Link Framework June 2011
[RFC4201] Kompella, K., "Link Bundle in MPLS Traffic Engineering",
RFC 4201, March 2005.
[RFC5036] Andersson, L., "LDP Specification", RFC 5036 , October
2007.
[RFC5712] Meyer, M., "MPLS Traffic Engineering Soft Preemption",
January 2010.
9.2. Informative References
[CL-REQ] Villamizar, C. and McDysan, D, "Requirements for MPLS Over
Composite Link", Oct. 2010, Work in Progress
[ENTROPY] Kompella, K. and S. Amante, "The Use of Entropy Labels in
MPLS Forwarding", draft-ietf-mpls-entropy-label-00.txt, May 2011,
Work in Progress
[FAT-PW] Bryan, S., et. Al, "Flow Aware Transport of Pseudowire over
an MPLS PSN", draft-ietf-pwe3-fat-pw-06, May. 2011, Work in progress
[MLSP] Kompella, K. "Multi-path Label Switched Paths Signaled Using
RSVP-TE", draft-kompella-mpls-rsvp-ecmp-00.txt, July 2010, Work in
Progress
10. Acknowledgments
Authors would like to thank Adrian Farrel, Fred Jounay, Yuji Kamite
for his extensive comments and suggestions, Ron Bonica, Nabil Bitar,
Eric Gray, Lou Berger, and Kireeti Kompella for their reviews and
great suggestions.
So, et al. Expires December 2011 [Page 10]
Internet-Draft Composite Link Framework June 2011
Authors' Addresses
So Ning
Verizon
2400 N. Glem Ave.,
Richerdson, TX 75082
Phone: +1 972-729-7905
Email: ning.so@verizonbusiness.com
Andrew Malis
Verizon
117 West St.
Waltham, MA 02451
Phone: +1 781-466-2362
Email: andrew.g.malis@verizon.com
Dave McDysan
Verizon
22001 Loudoun County PKWY
Ashburn, VA 20147
Email: dave.mcdysan@verizon.com
Lucy Yong
Huawei USA
1700 Alma Dr. Suite 500
Plano, TX 75075
Phone: +1 469-229-5387
Email: lucyyong@huawei.com
Curtis Villamizar
Infinera
Email: cvillamizar@infinera.com
Tony Li
Cisco Systems
Email: tony.li@tony.li
So, et al. Expires December 2011 [Page 11]