A local area network (LAN) must have the ability to carry a large amount of data with minimal delay. Very large corporate LANs often have round trip delays of 1-3 milliseconds under heavy loads. To give you an idea of ​​how fast it is, the human ear can only recognize delays of 125 milliseconds or more during a phone conversation. Anything less than 125 milliseconds seems like an instant response to us.

But sometimes the expectations of a high performance LAN are not met. Below are my top 5 causes of a slow LAN in no particular order.

1. Faulty hoses – The easiest way to identify faulty connection cables is to replace them. For example, if you experience delays between two particular computers, you can replace the connecting cables between the computer and the switch. If the switch is connected to structured cabling, you must also replace the patch between the patch panel and the switch.

2. Defective physical hardware – Switch ports that connect computers to switches can sometimes be physically damaged, causing intermittent connection issues. The best way to ensure that one switch port is not causing slow LAN performance is to connect the computer to a different switch port. Make sure the new switch port is in the same VLAN (if VLANs apply), is not powered down, and does not have MAC address level security applied. If there is a noticeable difference when you connect to the new port, you may have discovered a faulty switch port.

3. Circuit breaker overloaded – Switches are built with high performance in mind, but sometimes the accumulated pressure of many connected computers can cause switches to have performance issues. This is typically only an issue when the switch has been configured to perform additional functions such as QOS (Quality of Service), VACLs (Vlan Access Lists), or the switch hosts a large number of VLANs and tree instances. expansion. One sign of an overloaded switch is high utilization of the switch’s CPU.

4. Connected to a hub – Note the difference between a hub and a switch. A switch provides intelligence behind the switching function, ensuring packets are forwarded efficiently. A hub is completely inefficient and forwards all packets out of all ports; this is a shared Ethernet architecture and does not scale well with many connected computers or when a large amount of traffic traverses the hub because each packet competes for time on the network with every other packet causing collisions and retransmissions.

5. Half duplex connections – Modern network interface cards have the ability to run at half duplex for backwards compatibility with older equipment such as hubs. When a network interface card is configured for half duplex, it must send and receive data over the same cable, creating the possibility of collisions between incoming and outgoing traffic. Full duplex is the alternative and it is much more efficient to use one cable to send traffic and another to receive traffic, which eliminates the problem of Ethernet frame collisions.