A computer network is often spread across multiple switches. Trunk ports are usually used to connect switches together. There are two issues with using only a single physical link for the trunk connection.

• A single trunk link or port represents a single point of failure. So further no one can exchange data frames when the trunk port goes down because all other ports on the switch will, using that one single trunk link to communicate across the network.
• All traffic is going through the single trunk link; sometimes the link will fail to carry and move all the traffic smoothly. Because of the slow speed, the trunk link unable to carry the traffic.

So, if we want to transmit the traffic gently through the trunk links simply we need to increase the speed of the trunk link, 

However, simply connecting two or more ports/Links between the switches to increase the link speed will not work and one of two things will occur 

(1) Spanning Tree Protocol (STP) will disable one or more ports to eliminate the Ethernet loop.

(2) If STP is disabled, the result we will get is switching loop. Here is the reason why we need to use the aggregation protocols.

Port or Link Aggregation Protocol allows multiple physical ports to be bundled together to form a single logical port. The switch and STP (Spanning Tree Protocol) will treat the bundled ports as a single interface, eliminating the possibility of a switching loop.

Aggregation protocols support Fast, Gigabit, and 10 Gigabit Ethernet ports. A maximum of 8 active ports are supported in a single Switch. If the ports are operating in full duplex, the maximum theoretical bandwidth supported is as follows:

� Fast Ethernet � 800 Mbps 

� Gigabit Ethernet � 8 Gbps 

� 10 Gigabit Ethernet � 80 Gbps

 The previous section described the benefits of port or link aggregation for a trunk connection. However, aggregation protocols can be formed with either access or trunk ports. Aggregation protocols are also supported on Layer-3 interfaces.

Implementing aggregation protocols for access ports provides increased bandwidth and redundancy to a host device, such as a server. However, the host device must support a port aggregation protocol, such as LACP or PAGP.

If a port in the bundle fails, traffic will be redistributed across the remaining ports in the bundle. This happens nearly directly.