STP with Port Channels.

[D Prasanna Kumar Reddy]

Hi All,

Can some one please tell me How STP will calculate Cost over Portchannels ?

Lets say we have two Gigs Channeled together - Does it take this as 4 or 8 ?

And Why CDP will not detect Portchannels ? It will show as two entries in Neighbor table but not Portchannel. 

Thanks,

Prasanna Kumar Desireddy

[Mark Malone]

Hi
cdp detects physical ints only not logical

STP cost over pos
https://supportforums.cisco.com/t5/lan-switching-and-routing/stp-cost-of-port-channel/td-p/1423119

[Georg Pauwen]

Hello,

on a side note, I remember that in older (like 12.4) IOS versions you could specify the source interface for CDP:

Router(config)#cdp source-interface Loopback/Port-channel

I am not sure if this command is still around...

[paul driver]

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@D Prasanna Kumar Reddy wrote:

Hi All,

Can some one please tell me How STP will calculate Cost over Portchannels ?

Lets say we have two Gigs Channeled together - Does it take this as 4 or 8 ?

And Why CDP will not detect Portchannels ? It will show as two entries in Neighbor table but not Portchannel. 

Thanks,

Prasanna Kumar Desireddy

Hello

Just last me to add - Stp  cost of an ether-channel/portchannel is calculated from the aggregated bw of the physical links within that ether-channel  thus if an interface is removed from the PC the stp cost could be recalculated and as such initiate a stp topology change.

res

paul

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[Rolando Valenzuela]

Check this links:

https://supportforums.cisco.com/t5/lan-switching-and-routing/etherchannel-and-stp/td-p/1543214

https://www.netcraftsmen.com/port-channels-vpcs-and-spanning-tree-issues/

>>>>>>>>>>>>>>>>>>

About CDP read this: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-mt/cdp-15-mt-book/nm-cdp-discover.html#GUID-F729EBA3-2945-456F-9C1F-6CDD993CABEC

CDP learns about directly connected networks and it is consider a media-independent and network-independent protocol.