Te Metric (Is-Is And Ospf); Maintenance Of Te Links And Nodes - Alcatel-Lucent 7210 SAS M User Manual

Traffic Engineering

TE Metric (IS-IS and OSPF)

When the use of the TE metric is selected for an LSP, the shortest path computation after the TE
constraints are applied will select an LSP path based on the TE metric instead of the IGP metric.
The user configures the TE metric under the MPLS interface. Both the TE and IGP metrics are
advertised by OSPF and IS-IS for each link in the network. The TE metric is part of the traffic
engineering extensions of both IGP protocols.
A typical application of the TE metric is to allow CSPF to represent a dual TE topology for the
purpose of computing LSP paths.
An LSP dedicated for real-time and delay sensitive user and control traffic has its path computed
by CSPF using the TE metric. The user configures the TE metric to represent the delay figure, or a
combined delay/jitter figure, of the link. In this case, the shortest path satisfying the constraints of
the LSP path will effectively represent the shortest delay path.
An LSP dedicated for non delay sensitive user and control traffic has its path computed by CSPF
using the IGP metric. The IGP metric could represent the link bandwidth or some other figure as
required.
When the use of the TE metric is enabled for an LSP, CSPF will first prune all links in the network
topology that do not meet the constraints specified for the LSP path. These constraints include
bandwidth, admin-groups, and hop limit. CSPF will then run an SPF on the remaining links. The
shortest path among the all SPF paths will be selected based on the TE metric instead of the IGP
metric which is used by default. Note that the TE metric is only used in CSPF computations for
MPLS paths and not in the regular SPF computation for IP reachability.

Maintenance of TE links and Nodes

Graceful shutdown is used to maintain selective links and nodes in a TE network. Prior to a
shutdown, headend LER nodes are notified of the imminent shutdown of the links or nodes for the
purpose of maintenance, so the head-end nodes can move the paths of the LSPs away from the
affected resources. Modified TE parameters for the affected links are flooded so all other nodes in
the network avoid them in the CSPF calculations.
When the maintenance is over, the operator disables graceful shutdown, which reinstates and
floods the user-configured TE parameters. The restored links are available for LSP path
establishment.
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7210 SAS M, T, X, R6, Mxp MPLS Configura-