EN – Ether Channel

As I mentioned I will put up some CCNP stuff so here we go Ether Channel. Since I´m lacking real Switch hardware I sat it up on GNS3 / Dynamips.
First of all I added 2 x 3725 as Hosts than 2 x 3725 with NM-16ESW as “Switches”and connected both switches with 4 cables via interfaces fast ethernet 1/12 - 15.

The configuration of the Hosts is straight forward 
domain name, interface IP address 10.0.1.1 or 2 /24 speed and duplex

ip domain name EtherChannel.playingwithnetworks.com
int fast 0/0
speed 100
du fu
ip address 10.0.1.1 255.255.255.0
no shut


On the „switches“ you have to configure the Ether Channels. If you have a look on your spanning tree you´ll see that only the interface with the lowest interface number is in forwarding state all other interfaces connecting to your root bridge are in blocking state.

Switch_A#sh spanning-tree brief
VLAN1
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address c20a.1ed0.0000
Cost 19
Port 53 (FastEthernet1/12)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768
Address c20b.1ed0.0000
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300

Interface Designated
Name Port ID Prio Cost Sts Cost Bridge ID Port ID
-------------------- ------- ---- ----- --- ----- -------------------- -------
FastEthernet1/0 128.41 128 19 FWD 19 32768 c20b.1ed0.0000 128.41
FastEthernet1/12 128.53 128 19 FWD 0 32768 c20a.1ed0.0000 128.53
FastEthernet1/13 128.54 128 19 BLK 0 32768 c20a.1ed0.0000 128.54
FastEthernet1/14 128.55 128 19 BLK 0 32768 c20a.1ed0.0000 128.55
FastEthernet1/15 128.56 128 19 BLK 0 32768 c20a.1ed0.0000 128.56


The Ether Channel is configured by adding all physical interfaces to a channel group.


Interface range fast 1/12 – 15
Switchport trunk encryption dot1q
Switchport mode trunk
Channel-group 1 mode on


As soon as on both switches this configuration has been applied you can have another look into the spanning tree and you´ll see that the interfaces fastethernet 1/12 – 15 have vanished and only interface Port-channel 1 is in forwarding state.

Switch_A#sh spanning-tree brief

VLAN1
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address c20a.1ed0.0000
Cost 8
Port 321 (Port-channel1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768
Address c20b.1ed0.0000
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300

Interface Designated
Name Port ID Prio Cost Sts Cost Bridge ID Port ID
-------------------- ------- ---- ----- --- ----- -------------------- -------
FastEthernet1/0 128.41 128 19 FWD 8 32768 c20b.1ed0.0000 128.41
FastEthernet1/1 128.42 128 19 FWD 8 32768 c20b.1ed0.0000 128.42
Port-channel1 129.65 128 8 FWD 0 32768 c20a.1ed0.0000 129.65

Done ;)

Cheers NWG