What is EtherChannel?
EtherChannel is a port link aggregation technology used primarily on Cisco switches. It allows the grouping of several physical Ethernet links to create one logical channel that provides a bandwidth of up to 4 Gigabits per second (Gbps). EtherChannel has been available on Cisco Catalyst switches since the introduction of the Cisco Catalyst 6500 Series in 1999.
EtherChannel technology increases reliability and availability while also providing load-balancing and link-state redundancy. When used in conjunction with other high-availability technologies, such as Cisco Nonstop Forwarding (NSF) and Stateful Switchover (SSO), EtherChannel can provide a highly available infrastructure.
Protocols of EtherChannel
EtherChannel technology supports two main protocols:
Port Aggregation Protocol (PAgP)
PAgP is a Cisco-proprietary protocol that creates EtherChannels between two similar devices, such as two Cisco switches. PAgP packets are sent over the physical links that are to be aggregated and establish an agreement between the two devices on the formation of the EtherChannel.
Once PAgP has negotiated and formed the EtherChannel, it periodically sends packets to confirm that the physical links are still operational. If one of the physical links fails, PAgP dynamically reconfigures the EtherChannel to use only the working links.
Link Aggregation Control Protocol (LACP)
LACP is an IEEE (Institute of Electrical and Electronics Engineers) standard protocol that creates EtherChannels between devices that are not necessarily similar, such as a Cisco switch and a server with multiple Ethernet ports. LACP packets are sent over the physical links that are to be aggregated and establish an agreement between the two devices on the formation of the EtherChannel.
Once LACP has negotiated and formed the EtherChannel, it periodically sends packets to confirm that the physical links are still operational. If one of the physical links fails, LACP dynamically reconfigures the EtherChannel to use only the working links.
Advantages of EtherChannel
There are several advantages to using EtherChannel technology:
Increased bandwidth: By aggregating multiple physical links into a single logical link, EtherChannel increases the available bandwidth. This is especially important in applications where high bandwidth is required, such as video streaming or large file transfers.
Increased reliability and availability: By bundling multiple physical links into a single logical link, EtherChannel provides redundancy in the event of a link failure. In the event of a link failure, traffic is automatically re-routed to the working links.
Improved network performance: EtherChannel load-balances traffic across the physical links in the bundle and can improve network performance by distributing traffic evenly across the links.
Ease of configuration: EtherChannel technology can be configured manually or automatically using PAgP or LACP. Automatic configuration is recommended as it simplifies the configuration and reduces the potential for human error.
Compatibility: EtherChannel is compatible with a wide range of Cisco switches and routers, as well as third-party devices that support PAgP or LACP.
Drawbacks of EtherChannel
There are a few potential drawbacks to using EtherChannel technology:
Increased complexity: EtherChannel can increase the complexity of your network as it requires multiple physical links and potentially multiple switches.
Increased cost: EtherChannel requires the use of multiple physical links, which can increase the cost of your network infrastructure.
Requirement for similar devices: EtherChannel technology requires that the devices at either end of the EtherChannel are similar. This can be an issue when connecting a Cisco switch to a third-party device that does not support PAgP or LACP. In this case, manual configuration is required.
How to Configure EtherChannel?
EtherChannel technology can be configured manually or automatically using PAgP or LACP. Automatic configuration is recommended as it simplifies the configuration and reduces the potential for human error.
How to Configure LACP?
Follow these steps to configure LACP:
1. Connect the devices that you want to aggregate using multiple physical links.
2. Configure each device with the unique identifier (ID) that will be used to identify it to other devices in the EtherChannel. This can be of any value, but it must be unique.
3. Configure LACP on each device. This will enable the device to send LACP packets over the physical links.
4. The devices will exchange LACP packets and, if they are compatible, will form an EtherChannel.
5. If one of the physical links fails, LACP will dynamically reconfigure the EtherChannel to use only the working links.
Example with Command:
Router(config)#int e0/0
Router(config-if)#channel-group 1 mode active
Router(config-if)#int e0/1
Router(config-if)#channel-group 1 mode active
In the above example, we have configured LACP on two Ethernet interfaces and added them to channel group 1. This will create an EtherChannel between the two interfaces.