Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 98)

74 Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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MPLS CSPF fate-sharing group
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traversed. The path computation for a CSPF-enabled LSP uses the information from the TE
database to compute the best path for an LSP satisfying all constraints (bandwidth reservations,
network topology information, available resources), yet has the shortest distance to its destination.
The CSPF computation for an LSP only uses the information from the TE database at the time of
computation. Any future updates to the TE database do not cause the CSPF-enabled LSP to
recompute. Each CSPF fate-sharing group has an associated penalty (or cost) assigned to it. The
penalty associated with a CSPF fate-sharing group is used to direct the path computation for a
CSPF-enabled LSP away from TE links that share the same risk used by the set of TE links that the
protected path is using. The greater the penalty associated with a group, the less likely the
secondary or bypass LSP shares TE links used by the protected path.
A CSPF fate-sharing group is identified by a group name, and uses the following four ways to
identify elements in the TE database:
• Interface address - The interface address identifies all TE links by either the local address, or
the remote address matching the configured interface address.
• Point-to-point link - A point-to-point link identifies TE links by the local address and the remote
address on an interface. A point-to-point link specifies the from address and the to
address.The order in which the address is configured is not significant.
• Node - The node address is used to identify the device. All TE links from this device are
included.
• Subnet - The IP address with subnet mask identifies all TE links by either the local interface or
the remote address belonging to the configured subnet.
A CSPF fate-sharing group can be used in the following applications:
• The CSPF computation for setting up a secondary LSP when the associated primary LSP is in
an UP state.
• The CSPF computation for a backup path when selecting the bypass LSP tunnel.
• The CSPF computation for a bypass LSP path.
Refer to, “Configuring a MPLS CSPF fate-sharing group” for more information on configuring the
path computation for a CSPF-enabled LSP using CSPF fate-sharing group information.
Configuration considerations when using CSPF fate-sharing
group information
Consider the following when using CSPF fate-sharing group information:
NOTE
This release only supports a single mode of CSPF computation for a CSPF group by adding penalties
to each TE link's native IGP cost when it shares fate-sharing groups used by the protected path.
• CSPF computation using a CSPF group is only applicable when computing a secondary LSP
path, or when computing a backup path for selecting a bypass LSP. It is not applicable to the
primary or protected LSP path.
• CSPF calculates the least cost paths first and then applies the hop limit on the paths.
• CSPF computation using a CSPF group is used only for computing the secondary LSP path
when the primary LSP is in an UP state. In this case, CSPF collects group information from all
TE links used by the primary LSP. For each TE link, CSPF computes the total adjusted distance.
The total adjusted distance for each TE link is equal to the native IGP cost of the TE link plus
the sum of all penalties of the CSPF groups that the TE link is associated with, and used by the