EtherChannel Tutorial

In this short article we will configure some Layer 2 EtherChannel links. These are used to aggregate switchports to increase bandwidth and provide redundancy. I am running a four port EtherChannel from my Edge router to my Core switch. This article is useful for CCNP (BCMSN) studies.

First we will configure our switchports, then we will configure the Port-Channel interface, then we’ll look at some show commands.
Here is the switchport configuration:

interface range GigabitEthernet0/23 - 26 switchport trunk encapsulation dot1q switchport trunk native vlan 10 switchport mode trunk channel-group 1 mode on

We’ve set the trunking encapsulation to 802.1q and turn trunking on, then we set the native VLAN (I use 10), the command to note is “channel-group”, we have made the group 1 and set the mode to “on”, this means the port will not negotiate to become an EtherChannel, it just is.
Next we configure the Port-Channel interface:

interface Port-channel1 switchport trunk encapsulation dot1q switchport trunk native vlan 10 switchport mode trunk

This is just a logical interface (somewhat similar to a Loopback). We do the same trunk configuration here.
Now you will perform the same configuration on the other side, which I will leave out. Let’s look at some show commands:

CORE#sh etherchannel 1 summ Flags: D - down P - bundled in port-channel I - stand-alone s - suspended H - Hot-standby (LACP only) R - Layer3 S - Layer2 U - in use f - failed to allocate aggregator   M - not in use, minimum links not met u - unsuitable for bundling w - waiting to be aggregated d - default port   Number of channel-groups in use: 1 Number of aggregators: 1   Group Port-channel Protocol Ports ------+-------------+-----------+----------------------------------------------- 1 Po1(SU) - Gi0/21(P) Gi0/23(P) Gi0/25(P) Gi0/27(P)

This is currently my favorit show command, it sums things up nicely, without too much irrelevant information. It is telling us that our Layer 2 EtherChannel is up and working.
Here’s another useful show command:

CORE#sh etherchannel 1 port-channel Port-channels in the group: ---------------------------   Port-channel: Po1 ------------   Age of the Port-channel = 1d:18h:54m:09s Logical slot/port = 2/1 Number of ports = 4 GC = 0x00000000 HotStandBy port = null Port state = Port-channel Ag-Inuse Protocol = - Port security = Disabled   Ports in the Port-channel:   Index Load Port EC state No of bits ------+------+------+------------------+----------- 0 00 Gi0/21 On 0 0 00 Gi0/23 On 0 0 00 Gi0/25 On 0 0 00 Gi0/27 On 0   Time since last port bundled: 1d:16h:44m:47s Gi0/25 Time since last port Un-bundled: 1d:17h:00m:25s Gi0/27

This is similar information, but it also tells you how long the EtherChannel has been up, which can be helpful for troubleshooting.

We now have a four port, 400Mb/s (the ports on the Edge router are only FastEthernet) EtherChannel. This has been pretty brief, but there isn’t much more to it without getting into the negotiation protocols, which I try to avoid using.