Layer 3 Etherchannel on Cisco IOS Switch

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

A layer 3 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 3 interface, we configure an IP address on it.

I’ll be using two switches for this:

Etherchannel L3 Addresses

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:

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Forum Replies

  1. Hi Alan,

    1. This was an error which I just fixed. On both ends it should be “no switchport”. There’s two ways how you can create the Etherchannel, you could first manually create the port channel interface and add the physical interfaces or you can do what I did. If you assign physical interfaces to a non-existing port channel then it will be automatically created.

    2. Hmm I haven’t tried this but I guess it could work. It’s similar to connecting a router interface (L3 routed port) to a switch (L2 switchport).

    3. Load balancing is the same for L2 and L3 and you can

    ... Continue reading in our forum

  2. Hi Rene, you mention above that you have been able to get L3 PAgP working with VIRL. When I try, the etherchannel is always suspended at both ends. See output of ‘show etherchannel summary’ command.

    Group Port-channel Protocol Ports
    ------±------------±----------±----------------------------------------------
    1 Po1(RD) PAgP Gi0/1(s)

    I’ve tried ‘sudo vinstall bridge’ & restarting my VIRL vm as recommended on the VIRL discussion pages, however the problem persists and I continue to receive the log message:

    *Nov 2 10:48:04.907: %EC-5-L3DONTBNDL1: Gi0/1 suspended:

    ... Continue reading in our forum

  3. Thanks Rene for your response,

    Probably WLAN is not good choice of comparing to extended the network since CAPWAP is L3

    ... Continue reading in our forum

  4. Hi Santhosh,

    In this example you’ll have L2 interfaces from the access switch to the distribution switch with SVI interfaces for L3 so yes, you’ll have L2/L3 traffic over the same link. It works but it’s not what we normally do.

    With a design like this where we use trunks from the access layer to the distribution layer we normally don’t use SVI interfaces on the access layer. You can stick to cheaper L2 switches for the access layer and let the distribution layer do the routing…that’s where you configure SVI interfaces.

    Let me give you two examples for a typica

    ... Continue reading in our forum

  5. Hi Rene,
    Just my 2 cents, it should be worthwhile to mention that order of operation is crucial when creating L-3 port-channel. i.e. “no swithport” cmd must be entered 1st before entering “channel-group” command. If we enter the “channel-group” cmd first then port-channel will become layer-2 port-channel, and this operation is not revertible.

    Regards,
    Mehul

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