draft-ietf-tewg-te-metric-igp-02.txt   rfc3785.txt 
Francois Le Faucheur Network Working Group F. Le Faucheur
Ramesh Uppili Request for Comments: 3785 R. Uppili
Cisco Systems, Inc. BCP: 87 Cisco Systems, Inc.
Category: Best Current Practice A. Vedrenne
Alain Vedrenne P. Merckx
Pierre Merckx
Equant Equant
T. Telkamp
Thomas Telkamp
Global Crossing Global Crossing
May 2004
IETF Internet Draft Use of Interior Gateway Protocol (IGP) Metric
Expires: March, 2003 as a second MPLS Traffic Engineering (TE) Metric
Document: draft-ietf-tewg-te-metric-igp-02.txt September, 2002
Use of Interior Gateway Protocol (IGP) Metric as a second
MPLS Traffic Engineering Metric
Status of this Memo Status of this Memo
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Abstract Abstract
This document describes a common practice on how the existing metric This document describes a common practice on how the existing metric
of Interior Gateway Protocols (IGP) can be used as an alternative of Interior Gateway Protocols (IGP) can be used as an alternative
metric to the Traffic Engineering (TE) metric for Constraint Based metric to the Traffic Engineering (TE) metric for Constraint Based
Routing of MultiProtocol Label Switching (MPLS) Traffic Engineering Routing of MultiProtocol Label Switching (MPLS) Traffic Engineering
tunnels. This effectively results in the ability to perform tunnels. This effectively results in the ability to perform
Constraint Based Routing with optimization of one metric (e.g. link Constraint Based Routing with optimization of one metric (e.g., link
bandwidth) for some Traffic Engineering tunnels (e.g. Data Trunks) bandwidth) for some Traffic Engineering tunnels (e.g., Data Trunks)
while optimizing another metric (e.g. propagation delay) for some while optimizing another metric (e.g., propagation delay) for some
other tunnels with different requirements (e.g. Voice Trunks). other tunnels with different requirements (e.g., Voice Trunks). No
protocol extensions or modifications are required. This text
Le Faucheur, et. al 1
IGP Metric as second TE Metric September 2002
No protocol extensions or modifications are required. This text
documents current router implementations and deployment practices. documents current router implementations and deployment practices.
1. Introduction 1. Introduction
Interior Gateway Protocol (IGP) routing protocols (OSPF and IS-IS) Interior Gateway Protocol (IGP) routing protocols (OSPF and IS-IS) as
as well as MultiProtocol Label Switching (MPLS) signaling protocols well as MultiProtocol Label Switching (MPLS) signaling protocols
(RSVP-TE and CR-LDP) have been extended (as specified in [ISIS-TE], (RSVP-TE and CR-LDP) have been extended (as specified in [ISIS-TE],
[OSPF-TE], [RSVP-TE] and [CR-LDP]) in order to support the Traffic [OSPF-TE], [RSVP-TE] and [CR-LDP]) in order to support the Traffic
Engineering (TE) functionality as defined in [TE-REQ]. Engineering (TE) functionality as defined in [TE-REQ].
These IGP routing protocol extensions currently include These IGP routing protocol extensions currently include advertisement
advertisement of a single additional MPLS TE metric to be used for of a single additional MPLS TE metric to be used for Constraint Based
Constraint Based Routing of TE tunnels. 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
optimization criteria. For example, some Service Providers want to criteria. For example, some Service Providers want to perform
perform traffic engineering of different classes of service traffic engineering of different classes of service separately so
separately so that each class of Service is transported on a that each class of Service is transported on a different TE tunnel.
different TE tunnel. One example motivation for doing so is to apply One example motivation for doing so is to apply different fast
different fast restoration policies to the different classes of restoration policies to the different classes of service. Another
service. Another example motivation is to take advantage of separate example motivation is to take advantage of separate Constraint Based
Constraint Based Routing in order to meet the different Quality of Routing in order to meet the different Quality of Service (QoS)
Service (QoS) objectives of each Class of Service. Depending on QoS objectives of each Class of Service. Depending on QoS objectives one
objectives one may require either (a) enforcement by Constraint may require either (a) enforcement by Constraint Based Routing of
Based Routing of different bandwidth constraints for the different different bandwidth constraints for the different classes of service
classes of service as defined in [DS-TE], or (b) optimizing on a as defined in [DS-TE], or (b) optimizing on a different metric during
different metric during Constraint Based Routing or (c) both. This Constraint Based Routing or (c) both. This document discusses how
document discusses how optimizing on a different metric can be optimizing on a different metric can be achieved during Constraint
achieved during Constraint Based Routing. 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 Label Switched Paths (LSPs) that when Constraint Based Routing TE Label Switched Paths (LSPs) that
will be transporting voice, while optimizing a more usual metric will be transporting voice, while optimizing a more usual metric
(e.g. reflecting link bandwidth) when Constraint Based Routing TE (e.g., reflecting link bandwidth) when Constraint Based Routing TE
LSPs that will be transporting data. LSPs that will be transporting data.
Additional IGP protocol extensions could be defined so that multiple Additional IGP protocol extensions could be defined so that multiple
TE metrics could be advertised in the IGP (as proposed for example TE metrics could be advertised in the IGP (as proposed for example in
in [METRICS]) and would thus be available to Constraint Based [METRICS]) and would thus be available to Constraint Based Routing in
Routing in order to optimize on a different metric. However this order to optimize on a different metric. However this document
document describes how optimizing on a different metric can be describes how optimizing on a different metric can be achieved today
achieved today by existing implementations and deployments, without by existing implementations and deployments, without any additional
any additional IGP extensions beyond [ISIS-TE] and [OSPF-TE], by IGP extensions beyond [ISIS-TE] and [OSPF-TE], by effectively using
effectively using the IGP metric as a "second" TE metric. the IGP metric as a "second" TE metric.
2. Common Practice 2. Common Practice
Le Faucheur et. al 2
IGP Metric as second TE Metric September 2002
In current MPLS TE deployments, network administrators often want In current MPLS TE deployments, network administrators often want
Constraint Based Routing of TE LSPs carrying data traffic to be Constraint Based Routing of TE LSPs carrying data traffic to be based
based on the same metric as the metric used for Shortest Path on the same metric as the metric used for Shortest Path Routing.
Routing. Where this is the case, this practice allows the Constraint Where this is the case, this practice allows the Constraint Based
Based Routing algorithm running on the Head-End LSR to use the IGP Routing algorithm running on the Head-End LSR to use the IGP metric
metric advertised in the IGP to compute paths for data TE LSPs advertised in the IGP to compute paths for data TE LSPs instead of
instead of the advertised TE metric. The TE metric can then be used the advertised TE metric. The TE metric can then be used to convey
to convey another metric (e.g. a delay-based metric) which can be another metric (e.g., a delay-based metric) which can be used by the
used by the Constraint Based Routing algorithm on the Head-End LSR Constraint Based Routing algorithm on the Head-End LSR to compute
to compute path for the TE LSPs with different requirements (e.g. path for the TE LSPs with different requirements (e.g., Voice TE
Voice TE LSP). 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
the Head-End LSR to use the IGP metric advertised in the IGP to Head-End LSR to use the IGP metric advertised in the IGP to compute
compute paths for delay-sensitive TE LSPs (e.g. Voice TE LSPs) paths for delay-sensitive TE LSPs (e.g., Voice TE LSPs) instead of
instead of the advertised TE metric. The TE metric can then be used the advertised TE metric. The TE metric can then be used to convey
to convey another metric (e.g. bandwidth based metric) which can be another metric (e.g., bandwidth based metric) which can be used by
used by the Constraint Based Routing algorithm to compute paths for the Constraint Based Routing algorithm to compute paths for the data
the data TE LSPs. 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
of either the TE metric or the IGP metric, depending on the either the TE metric or the IGP metric, depending on the above
above configuration for the considered TE-LSP 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
metric to the IGP 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:
(i) it only allows TE tunnels to be routed on either of two (i) it only allows TE tunnels to be routed on either of two metrics
metrics (i.e. it cannot allow TE tunnels to be routed on one (i.e., it cannot allow TE tunnels to be routed on one of three,
of three, or more, metrics). Extensions (for example such as or more, metrics). Extensions (for example such as those
those proposed in [METRICS]) could be defined in the future proposed in [METRICS]) could be defined in the future if
if necessary to relax this constraints, but this is outside necessary to relax this constraints, but this is outside the
the scope of this document. scope of this document.
(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
one of the two metrics to be used for constraint based of the two metrics to be used for constraint based routing
routing (i.e. it cannot allow TE tunnels to be routed on (i.e., it cannot allow TE tunnels to be routed on either of two
either of two metrics while allowing IGP SPF to be based on a metrics while allowing IGP SPF to be based on a third metric).
third metric). Extensions (for example such as those proposed Extensions (for example such as those proposed in [METRICS])
in [METRICS]) could be defined in the future if necessary to could be defined in the future if necessary to relax this
relax this constraints, but this is outside the scope of this constraints, but this is outside the scope of this document.
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
so that an IGP metric is indeed advertised for the link. For 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 an example proposal on how to signal the LSP. See [PATH-COMP] for an example proposal on how to signal
which metric to optimize, to another component involved in path which metric to optimize, to another component involved in path
computation when RSVP-TE is used as the protocol to signal path computation when RSVP-TE is used as the protocol to signal path
computation 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
some migration scenarios may require that all head-end routers be migration scenarios may require that all head-end routers be upgraded
upgraded to the new implementation to avoid any disruption on to the new implementation to avoid any disruption on existing TE-LSPs
existing TE-LSPs before two metrics can effectively be used by TE. before two metrics can effectively be used by TE. The reason is that
The reason is that routers with current implementation are expected routers with current implementation are expected to always use the TE
to always use the TE metric for Constraint Based Routing of all metric for Constraint Based Routing of all tunnels; so when the TE
tunnels; so when the TE metric is reconfigured to reflect the metric is reconfigured to reflect the "second metric" (say to a
"second metric" (say to a delay-based metric) on links in the delay-based metric) on links in the network, then all TE-LSPs would
network, then all TE-LSPs would get routed based on the "second get routed based on the "second metric" metric, while the intent may
metric" metric, while the intent may be that only the TE-LSPs be that only the TE-LSPs explicitly configured so should be routed
explicitly configured so should be routed based on the "second based on the "second metric".
metric".
A possible migration scenario would look like this: A possible migration scenario would look like this:
1) upgrade software on all head-end routers in the network to 1) upgrade software on all head-end routers in the network to support
support this practice. this practice.
2) change the TE-LSPs configuration on the head-end routers to 2) change the TE-LSPs configuration on the head-end routers to use
use the IGP metric (e.g. bandwidth-based) for Constraint the IGP metric (e.g., bandwidth-based) for Constraint Based
Based Routing rather than the TE metric. Routing rather than the TE metric.
3) configure TE metric on the links to reflect the "second 3) configure TE metric on the links to reflect the "second metric"
metric" (e.g. delay-based). (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
need to be Constraint Based routed using the "second metric" to be Constraint Based routed using the "second metric" (e.g.,
(e.g. delay-based), and/or create new TE-LSPs with such a 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 document does not raise specific The practice described in this document does not raise specific
security issues beyond those of existing TE. Those are discussed in security issues beyond those of existing TE. Those are discussed in
the respective security sections of [TE-REQ], [RSVP-TE] and [CR- the respective security sections of [TE-REQ], [RSVP-TE] and [CR-LDP].
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.
6. Normative References 6. References
[TE-REQ] Awduche et al, Requirements for Traffic Engineering over 6.1. Normative References
MPLS, RFC2702, September 1999.
[OSPF-TE] Katz et al, Traffic Engineering Extensions to OSPF Version [TE-REQ] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M. and J.
2, draft-katz-yeung-ospf-traffic-07.txt, August 2002. McManus, Requirements for Traffic Engineering over MPLS,
RFC 2702, September 1999.
[ISIS-TE] Smit, Li, IS-IS extensions for Traffic Engineering, draft- [OSPF-TE] Katz, D., Kompella, K. and D. Yeung, "Traffic Engineering
ietf-isis-traffic-04.txt, August 2001. (TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
[RSVP-TE] Awduche et al, "RSVP-TE: Extensions to RSVP for LSP [ISIS-TE] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE),
RFC 3784, May 2004.
[RSVP-TE] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC3209, December 2001. Tunnels", RFC3209, December 2001.
[CR-LDP] Jamoussi et al., "Constraint-Based LSP Setup using LDP", [CR-LDP] Jamoussi, B., Andersson, L., Callon, R., Dantu, R., Wu,
RFC3212, January 2002 L., Doolan, P., Worster, T., Feldman, N., Fredette, A.,
Girish, M., Gray, E., Heinanen, J., Kilty, T. and A.
Malis, "Constraint-Based LSP Setup using LDP", RFC 3212,
January 2002.
7. Informative References 6.1. 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", Work in Progress, November 2000.
November 2000.
[DIFF-TE] Le Faucheur et al, "Requirements for support of Diff-Serv- [DIFF-TE] Le Faucheur, F. and W. Lai, "Requirements for Support of
aware MPLS Traffic Engineering", draft-ietf-tewg-diff-te-reqts- Differentiated Services-aware MPLS Traffic Engineering",
05.txt, June 2002. RFC 3564, July 2003.
[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-03.txt, June messages", Work in Progress, June 2002.
2002.
[LSP-HIER] Kompella et al, "LSP Hierarchy with Generalized MPLS TE", [LSP-HIER] Kompella, et al., "LSP Hierarchy with Generalized MPLS
draft-ietf-mpls-lsp-hierarchy-07.txt, June 2002. TE", Work in Progress, September 2002.
Authors' Address: 7. Authors' Addresses
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
Cisco Systems,
2000 Innovation Drive
Kanata,
ONTARIO,
Canada - K2K 3E8
Le Faucheur et. al 6 Phone: 01-613-254 4578
IGP Metric as second TE Metric September 2002
Cisco Systems, Inc.
300 Apollo Drive
Chelmsford, Massachussets 01824
USA
Phone: +1 978 244-4949
Email: ruppili@cisco.com Email: ruppili@cisco.com
Alain Vedrenne Alain Vedrenne
EQUANT Equant
400 Galleria Parkway Heraklion, 1041 route des Dolines, BP347
Atlanta, Georgia 30339 06906 Sophia Antipolis Cedex
USA FRANCE
Phone: +1 (678)-346-3466
Email: alain.vedrenne@equant.com Phone: +33 4 92 96 57 22
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, Ltd.
Oudkerkhof 51 Croeselaan 148
3512 GJ Utrecht NL-3521CG Utrecht
The Netherlands The Netherlands
Phone: +31 30 238 1250 Phone: +31 30 238 1250
E-mail: telkamp@gblx.net EMail: telkamp@gblx.net
Le Faucheur et. al 7 8. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
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