Layer 3 EtherChannel (2024)

Hello Everyone !!!

Happy Diwali..I hope everyone had a wonderful break and enjoyed every moment of Diwali.

So today I am going to talk about Layer 3 EtherChannel. In my previous article I did talk about the EtherChannel, please go through it if you want to take a glance.

Before jumping I would like to clear two points about the Port Channel and EtherChannel which you guys will encounter later in the article .

Strictly speaking, EtherChannel is the name that Cisco gives to its technology or architecture of Link Aggregation. Port channel is the name of the virtual port you create in a switch that binds the physical ports together, thus the Port-channel1, Port-channel2 or Po1 Po2 etc interfaces that you see in the configuration of the switch.In general however, Cisco and its users may use these two terms interchangeably.

Now coming back to our topic, in simple word we can say that EtherChannel allows to bundle to multiple links and to make them appear as only one link.

Alayer 3 EtherChannelis similar to an interface on a router. The switch won't “switch” traffic on this interface but route it. Because it's alayer 3interface, we configure an IP address on it.

I’ll be using two switches to explain the configuration part of it.

Before we configure the port channel settings you need to make sure that all interfaces have theexact sameconfiguration. Once you use thechannel-groupcommand, the port-channel interface will automatically inherit all settings from your physical interface. If you forget to run theno switchportcommand 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

Any idea what is the difference between EtherChannel layer 2 & layer 3?and where layer 2 is used and where layer 3 is used?

A layer2 etherchannel is seen as a single link by STP allowing to use all the member links for better performance. Most of the times a layer2 etherchannel is configured as a trunk ( 802.1Q more often) and can carry multiple Vlans/broadcast domains.

Layer2 etherchannels are best suited for interconnection of L2 LAN switches providing at the same time better performance and link fault tolerance.

For a Layer 2EtherChannel, physical ports are placed into anEtherChannelgroup.

In order to setup a L2 etherchannel acting as a trunk member links have to be configured at the same way:

same speed

same duplex

same trunking encapsulation protocol

same native vlan ( for 802.1Q)

the same list of Vlans permitted on each member link

A Layer3 etherchannel is likea single port configured in routed mode with no switchport, there is no concept of Vlans here, an IP address is associated to the port-channel logical interface, no ip address is configured under member interfaces. Layer3 port channel are used for interconnecting routers with routers or routers with multilayer switches for the same reasons of increased performance and link fault tolerance. No L2 signalling protocol including STP plays a role on Layer3 port channel.

For a Layer 3EtherChannel, layer 3 SVI (Switch Virtual Interface) is created, and then the physical ports are placed into an EtherChannelgroup which is bound to the L3 SVI.

In order to setup a L3 ether-channel acting as a trunk member links have to be configured at the same way:

same speed

same duplex

no switchport

L3 ether-channels are used in Service Provider networks to scale over 10GE speeds between core routers like CRS or ASR 9000 using bundles of 4 or more tengigabit interfaces.

Conclusion

Layer 2 EtherChannel bundles access or trunk ports between switches or other devices (e.g., servers).Layer 3 EtherChannel bundles routed ports between switches.