Spanning tree in Etherchannel

[holiveros]

Hi again,here are my questions:

1._ How does a fastetherchannel connection manages the link cost in a spanning tree topology. I mean, if a 100 Mbps has a cost of 19, what is the one for a fast etherchannel "200 Mbps" link.

2._ On the other hand (In fastetherchannel), I suppose that an individual physical link is put neither in blocked nor forwarding states (i mean as a individual link) since the distribution of traffic is made by other mechanisms (mac-address i.e.)...it should be treated as a channel, and the blocking or forwarding should be applied to the complete channel...am I correct..?

[Prashanth Krishnappa]

Question 1

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The cost of the channel is calculated by the formula:

cost of the channel = (sum of the costs of individual ports) / ( ( # of

ports) ^ 1.7 )

You would round up any decimal to the next high integer.

For example, A single GE's spant cost is 4:

and a 2 port channel would be (4+4)/(2^1.7)= 2.46 --> 3

and a 4 port channel would be (4+4+4+4)(4^1.7)=1.51 --> 2

cat6509-7b> (enable)sh port spant 4/1

------------------------ ---- ------------- --------- ---- -------- ----------

4/1 10 forwarding 4 32 disabled 0

4/2 10 forwarding 4 32 disabled 0

cat6509-7b> (enable) sh port spant 4/1

Port(s) Vlan Port-State Cost Prio Portfast Channel_id

------------------------ ---- ------------- --------- ---- -------- ----------

4/1-2 10 learning 3 32 disabled 865

cat6509-7b> (enable) sh port spant 4/1

Port(s) Vlan Port-State Cost Prio Portfast Channel_id

------------------------ ---- ------------- --------- ---- -------- ----------

4/1-4 10 learning 2 32 disabled 865

Question 2

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Correct for STP, all ports in the etherchannel is one logical port