Cisco Cisco IOS Software Release 12.2(27)SBC
MPLS Traffic Engineering—Configurable Path Calculation Metric for Tunnels
Feature Overview
2
Cisco IOS Release: Multiple releases (see the Feature History table)
Feature Overview
When Multiprotocol Label Switching (MPLS) traffic engineering (TE) is configured in a network, the
Interior Gateway Protocol (IGP) floods two metrics for every link: the normal IGP (Open Shortest Path
First (OSPF) or (Intermediate System-to-Intermediate System (IS-IS)) link metric and a TE link metric.
The IGP uses the IGP link metric in the normal way to compute routes for destination networks. In
previous releases, MPLS TE used the TE link metric to calculate and verify paths for TE tunnels. When
the traffic engineering metric was not explicitly configured, the traffic engineering metric was the IGP
metric.
Interior Gateway Protocol (IGP) floods two metrics for every link: the normal IGP (Open Shortest Path
First (OSPF) or (Intermediate System-to-Intermediate System (IS-IS)) link metric and a TE link metric.
The IGP uses the IGP link metric in the normal way to compute routes for destination networks. In
previous releases, MPLS TE used the TE link metric to calculate and verify paths for TE tunnels. When
the traffic engineering metric was not explicitly configured, the traffic engineering metric was the IGP
metric.
The current enhancement allows you to specify that the path calculation for a given tunnel be based on
either of the following:
either of the following:
•
IGP link metrics.
•
TE link metrics, which you can configure so that they represent the needs of a particular application.
For example, the TE link metrics can be configured to represent link transmission delay.
For example, the TE link metrics can be configured to represent link transmission delay.
Benefits
When TE tunnels are used to carry two types of traffic, this enhancement allows you to tailor tunnel path
selection to the requirements of each type of traffic.
selection to the requirements of each type of traffic.
For example, suppose certain tunnels are to carry voice traffic (which requires low delay) and other
tunnels are to carry data. In this situation, you can use the TE link metric to represent link delay and do
the following:
tunnels are to carry data. In this situation, you can use the TE link metric to represent link delay and do
the following:
•
Configure tunnels that carry voice to use the TE link metric set to represent link delay for path
calculation.
calculation.
•
Configure tunnels that carry data to use the IGP metric for path calculation.
Restrictions
Unless explicitly configured, the TE link metric for a given link is the IGP link metric. When the TE link
metric is used to represent a link property that is different from cost/distance, you must configure every
network link that can be used for TE tunnels with a TE link metric that represents that property by using
the mpls traffic-eng administrative-weight command. Failure to do so might cause tunnels to use
unexpected paths.
metric is used to represent a link property that is different from cost/distance, you must configure every
network link that can be used for TE tunnels with a TE link metric that represents that property by using
the mpls traffic-eng administrative-weight command. Failure to do so might cause tunnels to use
unexpected paths.
Related Features and Technologies
The configurable path calculation metric feature is related to MPLS traffic engineering.