Configuring EtherChannel

Configuring EtherChannel
To create an EtherChannel bundle, use the set port channel command. You must first make
sure that all the conditions for EtherChannel have been met.
Using Redundant Links with STP 521
Notice the switch output when we try to configure the ports on our 4000 switch as a bundle
to the 2950 switch:
Terry_4000> (enable) set port channel 1/1-2 on
Mismatch in trunk mode.
Mismatch in port duplex.
Mismatch in STP port priority.
Failed to set port(s) 1/1-2 channel mode to on.
Terry_4000> (enable)
There is a mismatch in trunking, duplex, and STP port priority. All the ports must be configured
the same for EtherChannel to work.
To view the configuration of a port, use the show port capabilities slot/port command:
Terry_4000> (enable) show port capabilities 1/1
Model WS-X5509
Port 1/1
Type 100BaseTX
Speed 100
Duplex half,full
Trunk encap type ISL
Trunk mode on,off,desirable,auto,nonegotiate
Channel 1/1-2
Broadcast suppression percentage(0-100)
Flow control no
Security yes
Membership static,dynamic
Fast start yes
Rewrite no
Terry_4000> (enable)
The preceding output shows the card model number and the configuration of the port. The
easiest way for us to make sure all the ports we want to channel are configured the same is to
just clear the configuration. We’re not suggesting that you just clear your config whenever any
problems come up, but the configuration we created in this chapter is pretty extensive, and it’s
easier to simply clear it out of the switch to perform the next function:
Terry_4000> (enable) clear config all
This command will clear all configuration in NVRAM.
This command will cause ifIndex to be reassigned on the next system startup.
Do you want to continue (y/n) [n]? y
........
.................
System configuration cleared.
Console> (enable)
522 Chapter 16  Using Spanning Tree with VLANs
Remember that you need to reset the switch after erasing the configuration to clear the configuration.
We need to reconfigure the switch with an IP address and trunking on ports 1/1 and
1/2. We’re also going to delete the configuration on the 2950, so then we will have both switches
back to our STP default:
Terry_2950#erase startup-config
Erasing the nvram filesystem will remove all files! Continue? [confirm]
Now that we have both the switches back to their default configurations, we’ll just configure
the host names and IP addresses and turn on trunking on ports 1/1 and 1/2 of the 4000 and
ports fa0/1 and fa0/24 of the 2950:
#configure terminal
(config)#hostname Terry_2950
Terry_2950(config)#int vlan 1
Terry_2950(config-if)#ip address 172.16.10.2 255.255.255.0
Terry_2950(config-if)#exit
Terry_2950(config)#ip default-gateway 172.16.10.1
Terry_2950(config)#int fa 0/1
Terry_2950(config-if)#switchport ?
access Set access mode characteristics of the interface
host Set port host
mode Set trunking mode of the interface
nonegotiate Device will not engage in negotiation protocol on this
interface
port-security Security related command
priority Set appliance 802.1p priority
protected Configure an interface to be a protected port
trunk Set trunking characteristics of the interface
voice Voice appliance attributes
Terry_2950(config-if)#switchport mode trunk
Terry_2950(config-if)#int fa 0/24
Terry_2950(config-if)#switchport mode trunk
Terry_2950(config-if)#^Z
Console> (enable) set prompt Terry_4000>
Terry_4000> (enable) set interface sc0 172.16.10.4 255.255.255.0

Interface sc0 IP address and netmask set.
Terry_4000> (enable) set trunk 1/1 on
Port(s) 1/1 trunk mode set to on.
Terry_4000> (enable) set trunk 1/2 on
Port(s) 1/2 trunk mode set to on.
Terry_4000> (enable)
Using Redundant Links with STP 523
To verify that the ports are trunking, use the show trunk command:
Terry_4000> (enable) show trunk
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ---------- -----------
1/1 on isl trunking 1
1/2 on isl trunking 1
Let’s try to configure EtherChannel between the switches again:
Terry_4000> (enable) set port channel 1/1-2 on
Port(s) 1/1-2 channel mode set to on.
Terry_4000> (enable) 2003 Jul 25 23:08:20 %PAGP-5
PORTFROMSTP:Port 1/1 left bridge port 1/1
2003 Jul 25 23:08:20 %PAGP-5-PORTFROMSTP:Port 1/2 left bridge port 1/2
2003 Jul 25 23:08:20 %PAGP-5-PORTTOSTP:Port 1/1 joined bridge port 1/1-2
2003 Jul 25 23:08:21 %PAGP-5-PORTTOSTP:Port 1/2 joined bridge port 1/1-2
To verify the EtherChannel bundle, use the show port channel command:
Terry_4000> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- --------- -------
1/1 errdisable on channel
1/2 errdisable on channel
----- ---------- --------- ----------- --------- -------
Terry_4000> (enable)
You can see that the status is error disabled and that no neighbors are found. This is because
we still need to configure Fast EtherChannel on the 2950 switch. If this were a remote switch, you
would lose contact with the switch and have to go to the site and console into the switch to configure
EtherChannel. You should configure the remote site first; then you will lose contact with
it until you configure the local switch bundle.
To configure the EtherChannel bundle on a 2950 switch, use the interface command
channel-group group_number mode mode_type:
Terry_2950(config)#int fa 0/1
Terry_2950(config-if)#channel-group ?
<1-6> Channel group number

Terry_2950(config-if)#channel-group 1 ?
mode Etherchannel Mode of the interface
524 Chapter 16  Using Spanning Tree with VLANs
Terry_2950(config-if)#channel-group 1 mode ?
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
Terry_2950(config-if)#channel-group 1 mode on
Terry_2950(config-if)#int fa 0/24
Terry_2950(config-if)#channel-group 1 mode on
Terry_2950(config-if)#exit
To view the channel status on the IOS-based switch, use the show etherchannel options
command.
Terry_2950#show etherchannel ?
<1-6> Channel group number
brief Brief information
detail Detail information
load-balance Load-balance/frame-distribution scheme among ports in
port-channel
port Port information
port-channel Port-channel information
summary One-line summary per channel-group
Terry_2950#show etherchannel det
Channel-group listing:
-----------------------


Group: 1
----------
Group state = L2
Ports: 3 Maxports = 8
Port-channels: 1 Max Port-channels = 1
Ports in the group:
-------------------
Port: Fa0/1
------------
Port state = Up Mstr In-Bndl
Channel group = 1 Mode = On/FEC Gcchange = 0
Port-channel = Po1 GC = 0x00010001 Pseudo port-channel = Po1
Port index = 0 Load = 0x00
Using Redundant Links with STP 525
Age of the port in the current state: 00d:00h:10m:25s
Port: Fa0/24
------------
Port state = Up Mstr In-Bndl
Channel group = 1 Mode = On/FEC Gcchange = 0
Port-channel = Po1 GC = 0x00010001 Pseudo port-channel = Po1
Port index = 0 Load = 0x00
Age of the port in the current state: 00d:00h:05m:45s
Port-channels in the group:
----------------------
Port-channel: Po1
------------
Age of the Port-channel = 00d:00h:10m:26s
Logical slot/port = 1/0 Number of ports = 2
GC = 0x00010001 HotStandBy port = null
Port state = Port-channel Ag-Inuse
Ports in the Port-channel:
Index Load Port EC state
------+------+------+------------
0 00 Fa0/1 on
0 00 Fa0/24 on
Time since last port bundled: 00d:00h:05m:45s Fa0/24
To verify the EtherChannel on the 4000 series switch, use the show port channel command:
Terry_4000> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- ------------------ ----------
1/1 connected on channel cisco 2950 Terry_2950 A
1/2 connected on channel cisco 2950 Terry_2950 B
----- ---------- --------- ----------- ------------------ ----------
Terry_4000> (enable)
526 Chapter 16  Using Spanning Tree with VLANs
The preceding switch output shows the port numbers, status, mode, channel status, neighbor
device, and neighbor port ID. Our EtherChannel is working!