LAG Features
Page 46 7210 SAS M, T, X, R6, R12, Mxp, S, Sx Interface Configuration Guide
links regardless of the specified port threshold action. If the port-threshold is met and
the action is set to dynamic cost, then the path cost is dynamically recalculated
regardless of the global dynamic cost configuration.
Enabling dynamic costing causes the physical link metrics used by OSPF to be
applied based on the operational or aggregate link bandwidth in the LAG that is
available at the time, providing the number of links that are up exceeds the configured
LAG port threshold value. If the number of available links falls below the configured
threshold, the configured threshold action determines if and at what cost this LAG
will be advertised.
For example, assume a single link in OSPF has an associated cost of 100 and the LAG
consists of four physical links. The cost associated with the logical link is 25. If one
link fails then the cost would automatically be adjusted to 33.
If dynamic cost is not configured then costing is applied based on the total number of
links configured. The cost would be calculated at 25. This will remain static provided
the number of links that are up exceeds the configured LAG threshold.
− LAG port threshold
The LAG port threshold feature allows configuration of the behavior, once the
number of available links in a LAG falls below or is equal to the specified threshold.
Two options are available:
1. If the number of links available (up) in a LAG is less than the configured threshold, then the
LAG is regarded as operationally down.
For example, assume a LAG consists of four physical links. The threshold is set to two and
dynamic costing is not configured. If the operational links is equal to or drops below two, the
link is regarded as operationally down until the number of operational links is two or more.
2. When the number of links available in a LAG is less than the configured threshold, the LAG
starts using the dynamic-cost allowing other nodes to adjust their routing tables according to
the revised costs. In this case, when the threshold is not crossed, a fixed metric (all links oper-
ational) is advertised.
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