Riverstone Networks WICT1-12 - Manual (Page 410)

17-102 Riverstone Networks RS Switch Router User Guide Release 8.0
Traffic Engineering MPLS Configuration
17.7 TRAFFIC ENGINEERING
One of the most important applications of MPLS is traffic engineering. Traffic engineering allows you to optimize the
utilization of network resources and traffic performance throughout a network. Traffic engineering does not mean that
the shortest path is always selected—traditional shortest path routing, as determined by interior gateway protocols
(IGPs), can cause both network congestion and the overuse of certain network paths, while longer paths are
under-utilized. Traffic engineering allows more efficient use of available bandwidth while avoiding congestion.
Packets with the same source and destination addresses can travel completely different paths in the network.
With MPLS, explicit LSPs can provide traffic engineering. For example, you can configure two explicit paths to the
same destination, with one the primary and the other the secondary path. However, explicit LSPs require you to
configure the paths on the ingress router. More dynamic traffic engineering can be performed with constraint-based
LSPs.
Traffic engineering requires extensions to the IGP. The RS provides extensions to OSPF and IS-IS IGPs to support
traffic engineering with MPLS. Traffic engineering is disabled by default for OSPF and IS-IS on RS routers.
This section discusses some of the features of traffic engineering and provides example configurations.
17.7.1 Administrative Groups
An MPLS administrative group 3 designates certain link attributes that can be used to impose additional path
constraints. Administrative groups can be used to contain certain traffic trunks within specific topological regions of
an MPLS network. You can employ administrative groups for path setup and selection for constrained path LSPs. You
can use administrative groups to:
• Apply the same policies to a set of resources that are not necessarily in the same topological area.
• Specify the relative preference of a set of resources for placement of traffic trunks.
• Restrict the placement of traffic trunks to specific sets of resources.
• Implement general include/exclude policies.
• Enforce policies that contain local traffic within specific regions of the network.
• Identify a particular set of resources.
For example, all OC-48 links in a network may be assigned to a particular administrative group. You can also assign
subsets of the OC-48 links to other administrative groups.
If you use administrative groups, the names of the groups and their corresponding decimal values must be the same on
all routers within the domain. You can configure up to 32 administrative groups in an MPLS domain.
You can specify one or more administrative groups to be included or excluded from an LSP computation. If you include
any administrative groups in an LSP computation, each selected link will have at least one included group. If you
exclude specific administrative groups in an LSP computation, each selected link cannot have any excluded groups. If
you include or exclude administrative groups in an LSP computation, links that do not have an associated group are
not considered. You can configure administrative group constraints for an LSP, or for a primary or secondary LSP. You
can include or exclude a maximum of 16 administrative groups for an LSP, or for a primary or secondary path.
You can assign one or more administrative groups to a router interface. IGPs use administrative groups to provide
information, such as IGP topology, to all routers in the domain.
If you change the administrative group for an LSP, the route is recalculated and the LSP may be rerouted. If you
change the administrative group for an interface, the change affects only new LSPs on the interface.
3. Administrative groups are referred to as resource classes or link colors in some implementations.