How to configure an Etherchannel + Etherchannel port number

[Steph1963]

Hi,

1) Can somebody indicate me where we should use the switchport mode trunk command when we want to configure an Etherchannel

Should we use the switchport mode trunk/switchport trunk encapsulation dot1q commands under the interface Port-Channe1 and under all interfaces that are part of the Etherchannel.

I am not sure if the configuration under the interface Port-Channel will automatically reflect under the interface configuration or we really have to duplicate the same configuration under interface Port-Channel and interface fa0/x (part of the same Etherchannel)

2) Can somebody explain me how the port number of the channel is derived.

In the following example, the port-channel 1 is numbered 201, how does the 201 is calcultated. The port cost is 12, is 12 a default for an Etherchannel port independant of the number of bundled interface or can it change depending on how many interfaces are used.

show spanning-tree vlan 10

DSW1#show spanning-tree vlan 10

VLAN10 is executing the ieee compatible Spanning Tree protocol

Bridge Identifier has priority 24576, address c407.0853.0001

Configured hello time 2, max age 20, forward delay 15

We are the root of the spanning tree

Topology change flag not set, detected flag not set

Number of topology changes 1 last change occurred 00:03:50 ago

from Port-channel1

Times: hold 1, topology change 35, notification 2

hello 2, max age 20, forward delay 15

Timers: hello 0, topology change 0, notification 0, aging 0

Port 201 (Port-channel1) of VLAN10 is forwarding

Port path cost 12, Port priority 128, Port Identifier 128.201.

Designated root has priority 24576, address c407.0853.0001

Designated bridge has priority 24576, address c407.0853.0001

Designated port id is 128.201, designated path cost 0

Timers: message age 0, forward delay 0, hold 0

Number of transitions to forwarding state: 1

BPDU: sent 122, received 3

Thanks for your help

Stephane

[cadet alain]

Hi,

an etherchannel is just a logical bundling of physical ports.the interfaces you're bundling must be in same mode meaning all access ports or all trunk ports and in this case must have same allowed vlans and same native vlan.

if you change the mode on the etherchannel then all physical bundled ports will inherit the change but before creating the etherchannel you must configure the interfaces the same.

The more interfaces you bundle the lower the cost is gonna be because the higher the bandwidth.

For port number, I can't tell you how it is derived.

Regards.

Alain.

[Jon Marshall]

Stephane

2) Portchannel 1 is not numbered 201. What is numbered 201 is the physical port id that is part of the port-channel. How these numbers are derived is dependant on the switch ie. a 6500 uses slot + port number to come up with an STP port id.

The cost will change dependant on the number of links you have in the etherchannel. See the last table on this page for examples -

http://www.hojmark.net/stp-port-cost.html

Jon