In this lab I'll show you how to configure etherchannel on two Cisco 2950 switches. There are three ports on SW1 which link to the corresponding three ports on SW2. Ordinarily two of these links would be shutdown by STP to prevent a switching loop from occuring, however we will setup etherchannel to increase bandwidth and minimise the impact of a link failure by utilising all three ports. Because these three ports will now appear as one logical port, STP will not put any in blocking mode.

To do this we will create a port channel group which will consist of our three links:

SW2#configure terminal
SW2(config)#interface range fastethernet 0/6 - 8
SW2(config-if-range)#channel-group 1 mode desirable
Creating a port-channel interface Port-channel 1
SW1#configure terminal
SW1(config)#interface range fastethernet 0/6 - 8
SW1(config-if-range)#channel-group 1 mode desirable
Creating a port-channel interface Port-channel 1

That creates our etherchannel. We can then view the configuration using standard show commands:

SW2#show interface | include line
Vlan1 is administratively down, line protocol is down
FastEthernet0/1 is down, line protocol is down (notconnect)
FastEthernet0/2 is down, line protocol is down (notconnect)
FastEthernet0/3 is down, line protocol is down (notconnect)
FastEthernet0/4 is down, line protocol is down (notconnect)
FastEthernet0/5 is down, line protocol is down (notconnect)
FastEthernet0/6 is up, line protocol is up (connected)
FastEthernet0/7 is up, line protocol is up (connected)
FastEthernet0/8 is up, line protocol is up (connected)
FastEthernet0/9 is down, line protocol is down (notconnect)
FastEthernet0/10 is down, line protocol is down (notconnect)
FastEthernet0/11 is down, line protocol is down (notconnect)
FastEthernet0/12 is down, line protocol is down (notconnect)
Port-channel1 is up, line protocol is up (connected)

Using the show interface command, you can see the interface bandwidth (BW) is the combination of all three interfaces in the channel group (300000 Kbit)

SW1#show interface port-channel 1
Port-channel1 is up, line protocol is up (connected)
  Hardware is EtherChannel, address is 000a.8ab9.7e46 (bia 000a.8ab9.7e46)
  MTU 1500 bytes, BW 300000 Kbit, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Full-duplex, 100Mb/s, media type is unknown media type
  input flow-control is off, output flow-control is off
  Members in this channel: Fa0/6 Fa0/7 Fa0/8
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:30, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 2000 bits/sec, 4 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     140 packets input, 14252 bytes, 0 no buffer
     Received 131 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 131 multicast, 0 pause input
     0 input packets with dribble condition detected
     37 packets output, 3791 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

For comparison the below shows the bandwidth of a standard fastethernet port (100000 Kbit).

SW1#show interface fastethernet 0/9
FastEthernet0/9 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 000a.8ab9.7e49 (bia 000a.8ab9.7e49)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 100BaseTX
  input flow-control is unsupported output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     104 packets input, 14131 bytes, 0 no buffer
     Received 75 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 55 multicast, 0 pause input
     0 input packets with dribble condition detected
     71 packets output, 6400 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

You can also use the show etherchannel x summary command to view details regarding the EtherChannel. One thing to note when creating an EtherChannel is both ends of the EtherChannel must use the same channel-group number otherwise the interface wont come up and you will see it in a down down state.

For more information on etherchannel and the channel group modes, see the Cisco article here: http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/relea...