Cisco Small Business Managed Switches (Linksys Business Series)

In a switched network, as the number of network users increases the available option for expanding the network is to cascade the switches. However, cascading 2 # 100 Mbps ports will not increase the line speed of the switches to more than 200 Mbps at full duplex mode.

Port trunking is a concept by which more than 1 # link can be combined thereby increasing the bandwidth between the switches. Port trunking allows multiple physical ports to appear as a single uplink port. Port trunking is a scalable solution. Hence, as and when the network traffic increases, the number of uplink ports can be increased. By having multiple links between switches or between switch and the server, even if a single link fails, the other port trunk takes care of the data transfer.

Implementing Port Trunking Between 2 # switches

When 2 # 10 / 100 switches are cascaded, 1 port from each switch is used for uplink functionality. The throughput between the switches can not exceed 200 Mbps when both switches operate at full duplex mode.

When both switches support port trunking, instead of 1 port, 4 ports from each switch can be used for cascading. The effective bandwidth between the switches increases up to 800 Mbps.

Implementing Port Trunking Between a Server and a Switch

Another scenario in which port trunking can be implemented is the connection between the server and the switch. In a client server based network, all the nodes try to communicate with the server. If the server is equipped with just 1 # 100 Mbps connection, the maximum throughput between the server and switch can be 200 Mbps in full duplex mode. When multiple clients try to access the server, the effective response time from the server to the node decreases.

For example, consider a Windows NT server equipped with a single port 10/100 TX card, the bandwidth between the server and the node can be a maximum of 200 Mbps in full duplex mode.

On the other hand, if the server is equipped with multi port network card, by loading the port trunking drivers in the server, all the network ports from the server can be connected to a single switch thereby multiplying the bandwidth between the server and switch.

For example consider a Windows NT server in which a 4 # port 10/100 PCI card is installed with port trunking drivers are configured. All the 4 # ports can be connected to the port trunking, increasing the bandwidth between the server and switch by 800 Mbps. This is almost close to a gigabit uplink speed between the server and the switch.

Identifying the Requirements for Port Trunking

To implement port trunking between switches, both switches should support port trunking.

In order to implement port trunking between a server and a switch, the server should have a multiport card with port trunking drivers loaded. The switch should support the port trunking feature.

The following needs to be taken care before configuring port trunking:

1. If one end of the connection is in a trunk port, the other end of the connection should be in the same trunk port. If it is not, the forwarding behavior of the trunk port will be unpredictable.
2. You should disable the ports in a trunk port until both ends of the link are configured.

Identifying the Benefits of Port Trunking?

1. Increases bandwidth between two switches.
   Port trunking allows more than 1 # link to be combined to provide a fat pipe between the switches, thereby increasing the bandwidth between the switches.
2. Scalable solution.
   Port trunking is a scalable solution. Hence, as and when the network traffic increases, the number of uplink ports to be used as a port trunk can be increased.
3. Increases bandwidth between the switch and the server.
   Port trunking can be implemented between a switch and the server. If the server is equipped with multi port network card, by loading the port trunking drivers in the server, all the network ports from the server can be connected to a single switch thereby multiplying the bandwidth between the server and switch.
4. Redundant links between two switches.
   By having multiple links between switches or between switch and the server, even if a single link fails, the other port trunk links takes care of the data transfer.