Layer 3 Etherchannel on Cisco IOS Switch

In a previous lesson I explained how Etherchannels work and how to configure them, but I didn’t write about layer 3 Etherchannels before. In this lesson, I’ll show you how to configure them.

A layer three etherchannel is similar to an interface on a router. The switch won’t “switch” traffic on this interface but route it. Because it’s a layer three interface, we configure an IP address on it.

I’ll be using two switches for this:

Before we configure the port channel settings, you need to make sure that all interfaces have the exact same configuration. Once you use the channel-group command, the port-channel interface will automatically inherit all settings from your physical interface. If you forget to run the no switchport command on an interface, your etherchannel will be layer 2 instead of layer 3!

Having said that, let’s configure our switches:

SW1(config)#interface range fastEthernet 0/1 - 2
SW1(config-if-range)#no switchport
SW1(config-if-range)#channel-group 12 mode on
Creating a port-channel interface Port-channel 12

SW2(config)#interface range fa0/1 - 2
SW2(config-if-range)#no switchport
SW2(config-if-range)#channel-group 12 mode on
Creating a port-channel interface Port-channel 12

This creates our Etherchannel. We can verify our work like this:

SW1#show etherchannel 12 summary 
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
------+-------------+-----------+-----------------------------------------------
12     Po12(RU)         -        Fa0/1(P)   Fa0/2(P)

Above, you can see that our port-channel 12 interface is layer 3, and it’s operational. Just like any other layer 3 interface, we can configure an IP address on this port-channel interface:

SW1(config)#interface port-channel 12
SW1(config-if)#ip address 192.168.12.1 255.255.255.0

SW2(config)#interface port-channel 12
SW2(config-if)#ip address 192.168.12.2 255.255.255.0

Let’s see if that works: