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Cat 6k Logical Port Calculation (as it relates to STP mode)

The release notes for CatOS on the Cat 6k discusses the logical port limits for each type of Supervisor Engine. According to the release notes, "the sum of all logical ports equals the number of trunks on the switch times the number of active VLANs on the trunks, plus the number of nontrunking ports on the switch." How should Etherchannel ports be counted? If you have a 4 port Etherchannel with 10 VLANs, is it 40 logical ports or just 10 logical ports?

  • Other Network Infrastructure Subjects
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Cisco Employee

Re: Cat 6k Logical Port Calculation (as it relates to STP mode)

Ports in an etherchannel are counted as individual ports, not as a single port, in the calculation.

The whole point of this calculation is to keep the spantree port management & processing within the constraints of what the CPU on the supervisor engine can handle. So at some level, the CPU still has to treat each port individually, even if logically they are a single link.

New Member

Re: Cat 6k Logical Port Calculation (as it relates to STP mode)

This is an interesting topic and so far I assumed that STP messages travel only through the Ag port and over one physical link. If this is true I am not able

to see CPU time used to justify an individual port count instead of an Ag port count. Please clarify, Thanks.

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