EtherChannel can be implemented in two ways, either statically or dynamically. In static mode, the network administrator manually configures the physical links that need to be bundled into a single logical link. The administrator needs to configure the same parameters on both ends of the physical links, such as the speed, duplex, and VLAN membership.
If you want to use manual (static) configuration, you must enable the EtherChannel functionality on each interface that should be included in the port channel by using the "On" mode. This way, the interfaces do not negotiate with each other by exchanging control packets but immediately become part of the port channel interface.
In dynamic mode, the devices negotiate the creation of an EtherChannel automatically. A special protocol detects the physical links between the switches and creates a logical link by aggregating the interfaces with similar characteristics.
Two protocols can be used for the EtherChannel deployment process:
- Cisco proprietary Port Aggregation Protocol (PAgP)
- Standard Link Aggregation Control Protocol (LACP)
If you are wondering which one is better, then neither is! They perform the same actions; the only difference is the terms used in the configuration process.
When you use PAgP or LACP, you must define the modes that interfaces will use. One mode defines the initiator of the establishment phase, while the other passively waits for the other side to start the negotiation process.
The active mode in PAgP is configured as "Desirable" while in LACP as "Active." The passive mode in PAgP is configured as "Auto," while in LACP as "Passive." Even though different terms are used, they perform the same actions, and based on the terms used in the configuration, you define the protocol you want to use.
Important: You cannot mix the PAgP and LACP protocols in a single EtherChannel configuration. You can use either of the protocols for an EtherChannel, but not both simultaneously.
The same applies to the static configuration. You must statically configure both devices to establish an EtherChannel, but you cannot use the static configuration on one side and either one of the dynamic protocols on the other.
EtherChannel Types
Depending on the type of interface (mode) you want to use for the EtherChannel, two different types of EtherChannel can be configured, and they are:
- Layer 2 EtherChannel
- Layer 3 EtherChannel
The main difference between Layer 2 and Layer 3 EtherChannel is the layer at which the technology operates. Layer 2 EtherChannel operates at the OSI model’s data link layer (Layer 2), while Layer 3 EtherChannel operates at the network layer (Layer 3).
As shown in the image above, Layer 2 EtherChannel bundles multiple physical links between two switches into a single logical link at Layer 2 and is typically used in the access layer of the networks.
Layer 3 EtherChannel combines multiple physical links between two routers or other devices with Layer 3 interfaces into a single logical link at Layer 3 and is used in the distribution or core layers of the network.