Where intermediate link speeds are created as a result of the aggregation of two or more links of the same
speed (see IEEE Std 802.3-2002), it can be appropriate to modify the recommended values shown in Table
17-3 to reflect the change in link speed. However, as the primary purpose of the Path Cost is to establish the
active topology of the network, it can be inappropriate for the Path Cost to track the effective speed of such
links too closely, as the resultant active topology could differ from that intended by the network
administrator. For example, if the network administrator had chosen an active topology that makes use of
aggregated links for resilience (rather than for increased data rate), it would be inappropriate to cause a
Spanning Tree topology change as a result of one of the physical links in an aggregation failing. Similarly,
with links that can autonegotiate their data rate, reflecting such changes of data rate in changes to Path Cost
is not necessarily appropriate, depending upon the intent of the network administrator. As a default, dynamic
changes of data rate shall not automatically cause changes in Port Path Cost.
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