What is EtherChannel ?
What is EtherChannel ?
EtherChannel is one of the features that make STP/RSTP better. Multiple physical links between two switches are treated as individual links and to avoid a loop one of the links works and the rest are put into a blocking state. However, if an EtherChannel is configured these physical links are known as EtherChannel which is a logical interface.
For an example you can see there are two different Port-Channels ( EtherChannel) Po1 and Po2 in the below sample diagram to clarify where they actually configured.
An Ethernet Switch considers an EtherChannel as a single link and it remains up until all physical links go down. Any physical link failure in EtherChannel does not cause STP convergence. EtherChannel in a network provides two major benefits – One, multiple links bandwidth is combined and there is more capacity available on EtherChannel to carry traffic compared to a single physical link.
Traffic is load-balanced across multiple links. Two, high availability as there are multiple links are bundled together, and in case of one link failure others can take care of traffic forwarding – without going through STP convergence.
There are two ways an EtherChannel is configured :
- Manual EtherChannel Configuration
- Dynamic EtherChannel Configuration
⭐ Manual EtherChannel Configuration 👇
The channel-group <number> mode on command is used to configure manual EtherChannel. This command needs to be entered for each physical link. All physical links that need to be part of the EtherChannel should use the same “<number>” argument in the command.
As per above image, there are 3 physical links between Switch 0 and Switch 1. The output from Switch 0 shows that only one interface Gi1/0/16 is in the forwarding state (Root) rest all are in the blocking state. The state of these ports is alternate which means in case of root port failure one of the links will be transitioned to forwarding and be a root port. Any link failure will cause STP to converge.
Till now it is clear, that there is no benefit of having multiple links between switches if we are not able to use them effectively. Although we have 100x 3 = 300Mbps of connections available but only 100 Mbps is usable as other physical ports are blocking. Ethernet solves this problem.
Will talk about the Dynamic EtherChannel configuration in another article.
