draft-ietf-tewg-te-metric-igp-00.txt   draft-ietf-tewg-te-metric-igp-01.txt 
skipping to change at line 14 skipping to change at line 14
Cisco Systems, Inc. Cisco Systems, Inc.
Alain Vedrenne Alain Vedrenne
Pierre Merckx Pierre Merckx
Equant Equant
Thomas Telkamp Thomas Telkamp
Global Crossing Global Crossing
IETF Internet Draft IETF Internet Draft
Expires: September, 2002 Expires: March, 2003
Document: draft-ietf-tewg-te-metric-igp-00.txt March, 2002 Document: draft-ietf-tewg-te-metric-igp-01.txt September, 2002
Use of IGP Metric as a second TE Metric Use of Interior Gateway Protocol Metric as a second
MPLS Traffic Engineering Metric
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are all provisions of Section 10 of RFC2026. Internet-Drafts are
Working documents of the Internet Engineering Task Force (IETF), its Working documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts. distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six
skipping to change at line 39 skipping to change at line 40
at any time. It is inappropriate to use Internet-Drafts as reference at any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Abstract Abstract
This draft describes a common practice on how the existing IGP This document describes a common practice on how the existing metric
Metric can be used as an alternative metric to the TE Metric for of Interior Gateway Protocols can be used as an alternative metric
Constraint Based Routing of MPLS TE Tunnels. This effectively to the Traffic Engineering metric for Constraint Based Routing of
results in the ability to perform Constraint Based Routing with MultiProtocol Label Switching Traffic Engineering tunnels. This
optimization of one metric (e.g. link bandwidth) for some TE Tunnels effectively results in the ability to perform Constraint Based
(e.g. Data Trunks) while optimizing another metric (e.g. propagation Routing with optimization of one metric (e.g. link bandwidth) for
delay) for some other TE Tunnels with different requirements (e.g. some Traffic Engineering tunnels (e.g. Data Trunks) while optimizing
Voice Trunks). another metric (e.g. propagation delay) for some other tunnels with
different requirements (e.g. Voice Trunks).
No protocol extensions or modifications are required. This text
documents current router implementations and deployment practices.
Le Faucheur, et. al 1 Le Faucheur, et. al 1
IGP Metric as second TE Metric March 2002 IGP Metric as second TE Metric September 2002
No protocol extensions or modifications are required. This text
documents current router implementations and deployment practices.
1. Introduction 1. Introduction
IGP routing protocols (OSPF and IS-IS) as well as MPLS Signaling Interior Gateway Protocol (IGP) routing protocols (OSPF and IS-IS)
protocols (RSVP-TE and CR-LDP) have been extended (as specified in as well as MultiProtocol Label Switching (MPLS) signaling protocols
[ISIS-TE], [OSPF-TE], [RSVP-TE] and [CR-LDP]) in order to support (RSVP-TE and CR-LDP) have been extended (as specified in [ISIS-TE],
the traffic engineering functionality as defined in [TE-REQ]. [OSPF-TE], [RSVP-TE] and [CR-LDP]) in order to support the Traffic
Engineering (TE) functionality as defined in [TE-REQ].
These IGP routing protocol extensions currently include These IGP routing protocol extensions currently include
advertisement of a single additional TE Metric to be used for advertisement of a single additional MPLS TE metric to be used for
Constraint Based Routing of TE Tunnels. Constraint Based Routing of TE tunnels.
However, the objective of traffic engineering is to optimize the use However, the objective of traffic engineering is to optimize the use
and the performance of the network. So it seems relevant that TE and the performance of the network. So it seems relevant that TE
tunnel placement may be optimized according to different tunnel placement may be optimized according to different
optimization criteria. For example, some Service Providers want to optimization criteria. For example, some Service Providers want to
perform traffic engineering of different classes of service perform traffic engineering of different classes of service
separately so that each class of Service is transported on a separately so that each class of Service is transported on a
different TE Tunnel. One example motivation for doing so is to apply different TE tunnel. One example motivation for doing so is to apply
different fast restoration policies to the different classes of different fast restoration policies to the different classes of
service. Another example motivation is to take advantage of separate service. Another example motivation is to take advantage of separate
Constraint Based Routing in order to meet the different QoS Constraint Based Routing in order to meet the different Quality of
objectives of each Class of Service. To achieve different QoS Service (QoS) objectives of each Class of Service. Depending on QoS
objectives may require enforcement by Constraint Based Routing of objectives one may require either (a) enforcement by Constraint
different bandwidth constraints for the different classes of service Based Routing of different bandwidth constraints for the different
as defined in [DS-TE]. In some Service Provider environments, it classes of service as defined in [DS-TE], or (b) optimizing on a
also requires optimizing on a different metric during Constraint different metric during Constraint Based Routing or (c) both. This
Based Routing. document discusses how optimizing on a different metric can be
achieved during Constraint Based Routing.
The most common scenario for a different metric calls for The most common scenario for a different metric calls for
optimization of a metric reflecting delay (mainly propagation delay) optimization of a metric reflecting delay (mainly propagation delay)
when Constraint Based Routing TE LSPs that will be transporting when Constraint Based Routing TE Label Switched Paths (LSPs) that
voice, while optimizing a more usual metric (e.g. reflecting link will be transporting voice, while optimizing a more usual metric
bandwidth) when Constraint Based Routing TE LSPs that will be (e.g. reflecting link bandwidth) when Constraint Based Routing TE
transporting data. LSPs that will be transporting data.
[METRICS] proposes extensions so that multiple TE Metrics can be Additional IGP protocol extensions could be defined so that multiple
advertised in the IGP. If/once those are fully specified and TE metrics could be advertised in the IGP (as proposed for example
implemented, they will address the above scenario. However this in [METRICS]) and would thus be available to Constraint Based
draft describes how the above scenario is currently addressed in the Routing in order to optimize on a different metric. However this
meantime by existing implementations and deployments, without any document describes how optimizing on a different metric can be
additional IGP extensions beyond [ISIS-TE] and [OSPF-TE], by achieved today by existing implementations and deployments, without
effectively using the IGP Metric as a "second" TE Metric. any additional IGP extensions beyond [ISIS-TE] and [OSPF-TE], by
effectively using the IGP metric as a "second" TE metric.
2. Common Practice 2. Common Practice
In current MPLS TE deployments, network administrators often want
Constraint Based Routing of TE LSPs carrying data traffic to be
based on the same metric as the metric used for Shortest Path
Le Faucheur et. al 2 Le Faucheur et. al 2
IGP Metric as second TE Metric March 2002 IGP Metric as second TE Metric September 2002
In current MPLS TE deployments, network administrators often want
Constraint Based Routing of TE LSPs carrying data traffic to be
based on the same metric as the metric used for Shortest Path
Routing. Where this is the case, this practice allows the Constraint Routing. Where this is the case, this practice allows the Constraint
Based Routing algorithm running on the Head-End LSR to use the IGP Based Routing algorithm running on the Head-End LSR to use the IGP
Metric advertised in the IGP to compute paths for data TE LSPs metric advertised in the IGP to compute paths for data TE LSPs
instead of the advertised TE Metric. The TE Metric can then be used instead of the advertised TE metric. The TE metric can then be used
to convey another metric (e.g. a delay-based metric) which can be to convey another metric (e.g. a delay-based metric) which can be
used by the Constraint Based Routing algorithm on the Head-End LSR used by the Constraint Based Routing algorithm on the Head-End LSR
to compute path for the TE LSPs with different requirements (e.g. to compute path for the TE LSPs with different requirements (e.g.
Voice TE LSP). Voice TE LSP).
In some networks, network administrators configure the IGP metric to In some networks, network administrators configure the IGP metric to
a value factoring the link propagation delay. In that case, this a value factoring the link propagation delay. In that case, this
practice allows the Constraint Based Routing algorithm running on practice allows the Constraint Based Routing algorithm running on
the Head-End LSR to use the IGP Metric advertised in the IGP to the Head-End LSR to use the IGP metric advertised in the IGP to
compute paths for delay-sensitive TE LSPs (e.g. Voice TE LSPs) compute paths for delay-sensitive TE LSPs (e.g. Voice TE LSPs)
instead of the advertised TE Metric. The TE Metric can then be used instead of the advertised TE metric. The TE metric can then be used
to convey another metric (e.g. bandwidth based metric) which can be to convey another metric (e.g. bandwidth based metric) which can be
used by the Constraint Based Routing algorithm to compute paths for used by the Constraint Based Routing algorithm to compute paths for
the data TE LSPs. the data TE LSPs.
More generally, the TE Metric can be used to carry any arbitrary More generally, the TE metric can be used to carry any arbitrary
metric that may be useful for Constraint Based Routing of the set of metric that may be useful for Constraint Based Routing of the set of
LSPs which need optimization on another metric than the IGP metric. LSPs which need optimization on another metric than the IGP metric.
2.1. Head-End LSR Implementation Practice 2.1. Head-End LSR Implementation Practice
A Head-End LSR implements the current practice by: A Head-End LSR implements the current practice by:
(i) Allowing configuration, for each TE LSP to be routed, of (i) Allowing configuration, for each TE LSP to be routed, of
whether the IGP Metric or the TE Metric is to be used by the whether the IGP metric or the TE metric is to be used by the
Constraint Based Routing algorithm. Constraint Based Routing algorithm.
(ii) Enabling the Constraint Based Routing algorithm to make use (ii) Enabling the Constraint Based Routing algorithm to make use
of either the TE Metric or the IGP Metric, depending on the of either the TE metric or the IGP metric, depending on the
above configuration for the considered TE-LSP above configuration for the considered TE-LSP
2.2. Network Deployment Practice 2.2. Network Deployment Practice
A Service Provider deploys this practice by: A Service Provider deploys this practice by:
(i) Configuring, on every relevant link, the TE Metric to reflect (i) Configuring, on every relevant link, the TE metric to reflect
whatever metric is appropriate (e.g. delay-based metric) for whatever metric is appropriate (e.g. delay-based metric) for
Constraint Based Routing of some LSPs as an alternative Constraint Based Routing of some LSPs as an alternative
metric to the IGP Metric metric to the IGP metric
(ii) Configuring, for every TE LSP, whether this LSP is to be (ii) Configuring, for every TE LSP, whether this LSP is to be
constraint based routed according to the TE Metric or IGP constraint based routed according to the TE metric or IGP
Metric metric
Le Faucheur et. al 3
IGP Metric as second TE Metric September 2002
2.3. Constraints 2.3. Constraints
The practice described in this document has the following The practice described in this document has the following
constraints: constraints:
Le Faucheur et. al 3 (i) it only allows TE tunnels to be routed on either of two
metrics (i.e. it cannot allow TE tunnels to be routed on one
IGP Metric as second TE Metric March 2002 of three, or more, metrics). Extensions (for example such as
those proposed in [METRICS]) could be defined in the future
(i) it only allows TE Tunnels to be routed on either of two if necessary to relax this constraints, but this is outside
metrics (i.e. it cannot allow TE Tunnels to be routed on one the scope of this document.
of three, or more, metrics). [METRICS] proposes extensions
which could be used to relax this constraints when necessary.
(ii) it can only be used where the IGP Metric is appropriate as (ii) it can only be used where the IGP metric is appropriate as
one of the two metrics to be used for constraint based one of the two metrics to be used for constraint based
routing (i.e. it cannot allow TE Tunnels to be routed on routing (i.e. it cannot allow TE tunnels to be routed on
either of two metrics while allowing IGP SPF to be based on a either of two metrics while allowing IGP SPF to be based on a
third metric). [METRICS] proposes extensions which could be third metric). Extensions (for example such as those proposed
used to relax this constraint when necessary. in [METRICS]) could be defined in the future if necessary to
relax this constraints, but this is outside the scope of this
document.
(iii) it can only be used on links which support an IGP adjacency (iii) it can only be used on links which support an IGP adjacency
so that an IGP Metric is indeed advertised for the link. For so that an IGP metric is indeed advertised for the link. For
example, this practice can not be used on Forwarding example, this practice can not be used on Forwarding
Adjacencies (see [LSP-HIER]). Adjacencies (see [LSP-HIER]).
Note that, as with [METRICS], this practice does not recommend that Note that, as with [METRICS], this practice does not recommend that
the TE Metric and the IGP metric be used simultaneously during path the TE metric and the IGP metric be used simultaneously during path
computation for a given LSP. This is known to be an NP-complete computation for a given LSP. This is known to be an NP-complete
problem. problem.
2.4. Interoperability 2.4. Interoperability
Where path computation is entirely performed by the Head-End (e.g. Where path computation is entirely performed by the Head-End (e.g.
intra-area operations with path computation on Head-end), this intra-area operations with path computation on Head-end), this
practice does not raise any interoperability issue among LSRs since practice does not raise any interoperability issue among LSRs since
the use of one metric or the other is a matter purely local to the the use of one metric or the other is a matter purely local to the
Head-End LSR. Head-End LSR.
Where path computation involves another component than the Head-End Where path computation involves another component than the Head-End
(e.g. with inter-area operations where path computation is shared (e.g. with inter-area operations where path computation is shared
between the Head-End and Area Boundary Routers or a Path Computation between the Head-End and Area Boundary Routers or a Path Computation
Server), this practice requires that which metric to optimize on be Server), this practice requires that which metric to optimize on, be
signaled along with the other constraints (bandwidth, affinity) for signaled along with the other constraints (bandwidth, affinity) for
the LSP. See [PATH-COMP] for a proposal on how to signal which the LSP. See [PATH-COMP] for an example proposal on how to signal
metric to optimize to another component involved in path computation which metric to optimize, to another component involved in path
when RSVP-TE is used as the protocol to signal path computation computation when RSVP-TE is used as the protocol to signal path
information. computation information.
3. Migration Considerations 3. Migration Considerations
Le Faucheur et. al 4
IGP Metric as second TE Metric September 2002
Service Providers need to consider how to migrate from the current Service Providers need to consider how to migrate from the current
implementation to the new one supporting this practice. implementation to the new one supporting this practice.
Although the head-end routers act independently from each other, Although the head-end routers act independently from each other,
some migration scenarios may require that all head-end routers be some migration scenarios may require that all head-end routers be
upgraded to the new implementation to avoid any disruption on upgraded to the new implementation to avoid any disruption on
existing TE-LSPs before two metrics can effectively be used by TE. existing TE-LSPs before two metrics can effectively be used by TE.
The reason is that routers with current implementation are expected The reason is that routers with current implementation are expected
Le Faucheur et. al 4
IGP Metric as second TE Metric March 2002
to always use the TE metric for Constraint Based Routing of all to always use the TE metric for Constraint Based Routing of all
tunnels; so when the TE metric is reconfigured to reflect the tunnels; so when the TE metric is reconfigured to reflect the
"second metric" (say to a delay-based metric) on links in the "second metric" (say to a delay-based metric) on links in the
network, then all TE-LSPs would get routed based on the "second network, then all TE-LSPs would get routed based on the "second
metric" metric, while the intent may be that only the TE-LSPs metric" metric, while the intent may be that only the TE-LSPs
explicitly configured so should be routed based on the "second explicitly configured so should be routed based on the "second
metric". metric".
A possible migration scenario would look like this: A possible migration scenario would look like this:
skipping to change at line 248 skipping to change at line 255
metric" (e.g. delay-based). metric" (e.g. delay-based).
4) modify the LSP configuration of the subset of TE-LSPs which 4) modify the LSP configuration of the subset of TE-LSPs which
need to be Constraint Based routed using the "second metric" need to be Constraint Based routed using the "second metric"
(e.g. delay-based), and/or create new TE-LSPs with such a (e.g. delay-based), and/or create new TE-LSPs with such a
configuration. configuration.
It is desirable that step 2 is non-disruptive (i.e. the routing of a It is desirable that step 2 is non-disruptive (i.e. the routing of a
LSP will not be affected in any way, and the data transmission will LSP will not be affected in any way, and the data transmission will
not be interrupted) by the change of LSP configuration to use "IGP not be interrupted) by the change of LSP configuration to use "IGP
Metric" as long as the actual value of the "IGP Metric" and "TE metric" as long as the actual value of the "IGP metric" and "TE
Metric" are equal on every link at the time of LSP reconfiguration metric" are equal on every link at the time of LSP reconfiguration
(as would be the case at step 2 in migration scenario above which (as would be the case at step 2 in migration scenario above which
assumed that TE Metric was initially equal to IGP Metric). assumed that TE metric was initially equal to IGP metric).
4. Security Considerations 4. Security Considerations
The practice described in this draft does not raise specific The practice described in this document does not raise specific
security issues beyond those of existing TE. security issues beyond those of existing TE. Those are discussed in
the respective security sections of [TE-REQ], [RSVP-TE] and [CR-
LDP].
5. Acknowledgment 5. Acknowledgment
Le Faucheur et. al 5
IGP Metric as second TE Metric September 2002
This document has benefited from discussion with Jean-Philippe This document has benefited from discussion with Jean-Philippe
Vasseur. Vasseur.
References 6. Normative References
[TE-REQ] Awduche et al, Requirements for Traffic Engineering over [TE-REQ] Awduche et al, Requirements for Traffic Engineering over
MPLS, RFC2702, September 1999. MPLS, RFC2702, September 1999.
Le Faucheur et. al 5 [OSPF-TE] Katz et al, Traffic Engineering Extensions to OSPF Version
2, draft-katz-yeung-ospf-traffic-07.txt, August 2002.
IGP Metric as second TE Metric March 2002
[OSPF-TE] Katz, Yeung, Traffic Engineering Extensions to OSPF,
draft-katz-yeung-ospf-traffic-06.txt, October 2001.
[ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft- [ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft-
ietf-isis-traffic-03.txt, June 2001. ietf-isis-traffic-04.txt, August 2001.
[RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP [RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", draft-ietf-mpls-rsvp-lsp-tunnel-08.txt, February 2001. Tunnels", RFC3209, December 2001.
[CR-LDP] Jamoussi et al., "Constraint-Based LSP Setup using LDP", [CR-LDP] Jamoussi et al., "Constraint-Based LSP Setup using LDP",
draft-ietf-mpls-cr-ldp-05.txt, February 2001 RFC3212, January 2002
7. Informative References
[METRICS] Fedyk et al, "Multiple Metrics for Traffic Engineering [METRICS] Fedyk et al, "Multiple Metrics for Traffic Engineering
with IS-IS and OSPF", draft-fedyk-isis-ospf-te-metrics-01.txt, with IS-IS and OSPF", draft-fedyk-isis-ospf-te-metrics-01.txt,
November 2000. November 2000.
[DS-TE] Le Faucheur et al, "Requirements for support of Diff-Serv- [DIFF-TE] Le Faucheur et al, "Requirements for support of Diff-Serv-
aware MPLS Traffic Engineering", draft-ietf-tewg-diff-te-reqts- aware MPLS Traffic Engineering", draft-ietf-tewg-diff-te-reqts-
02.txt, November 2001. 05.txt, June 2002.
[PATH-COMP] Vasseur et al, "RSVP Path computation request and reply [PATH-COMP] Vasseur et al, "RSVP Path computation request and reply
messages", draft-vasseur-mpls-path-computation-rsvp- 01.txt, messages", draft-vasseur-mpls-path-computation-rsvp-03.txt, June
November 2001. 2002.
[LSP-HIER] Kompella et al, "LSP Hierarchy with Generalized MPLS TE", [LSP-HIER] Kompella et al, "LSP Hierarchy with Generalized MPLS TE",
draft-ietf-mpls-lsp-hierarchy-04.txt, February 2002. draft-ietf-mpls-lsp-hierarchy-07.txt, June 2002.
Authors' Address: Authors' Address:
Francois Le Faucheur Francois Le Faucheur
Cisco Systems, Inc. Cisco Systems, Inc.
Village d'Entreprise Green Side - Batiment T3 Village d'Entreprise Green Side - Batiment T3
400, Avenue de Roumanille 400, Avenue de Roumanille
06410 Biot-Sophia Antipolis 06410 Biot-Sophia Antipolis
France France
Phone: +33 4 97 23 26 19 Phone: +33 4 97 23 26 19
Email: flefauch@cisco.com Email: flefauch@cisco.com
Ramesh Uppili Ramesh Uppili
Le Faucheur et. al 6
IGP Metric as second TE Metric September 2002
Cisco Systems, Inc. Cisco Systems, Inc.
300 Apollo Drive 300 Apollo Drive
Chelmsford, Massachussets 01824 Chelmsford, Massachussets 01824
USA USA
Phone: +1 978 244-4949 Phone: +1 978 244-4949
Email: ruppili@cisco.com Email: ruppili@cisco.com
Alain Vedrenne Alain Vedrenne
EQUANT EQUANT
400 Galleria Parkway 400 Galleria Parkway
Atlanta, Georgia 30339 Atlanta, Georgia 30339
Le Faucheur et. al 6
IGP Metric as second TE Metric March 2002
USA USA
Phone: +1 (678)-346-3466 Phone: +1 (678)-346-3466
Email: alain.vedrenne@equant.com Email: alain.vedrenne@equant.com
Pierre Merckx Pierre Merckx
EQUANT EQUANT
1041 route des Dolines - BP 347 1041 route des Dolines - BP 347
06906 SOPHIA ANTIPOLIS Cedex 06906 SOPHIA ANTIPOLIS Cedex
FRANCE FRANCE
Phone: +33 (0)492 96 6454 Phone: +33 (0)492 96 6454
Email: pierre.merckx@equant.com Email: pierre.merckx@equant.com
Thomas Telkamp Thomas Telkamp
Global Crossing Global Crossing
Olympia 6 Oudkerkhof 51
1213 NP Hilversum 3512 GJ Utrecht
The Netherlands The Netherlands
Phone: +31 35 655 651 Phone: +31 30 238 1250
E-mail: telkamp@gblx.net E-mail: telkamp@gblx.net
Le Faucheur et. al 7 Le Faucheur et. al 7
 End of changes. 

This html diff was produced by rfcdiff 1.25, available from http://www.levkowetz.com/ietf/tools/rfcdiff/