subject: Top 5 Network Issues That Can Cause Slow LAN Performance [print this page] Top 5 Network Issues That Can Cause Slow LAN Performance
A Local Area Network(LAN) should have the capacity to carry a large amount of data with minimum delay. Even very large corporate LANs often have 1 to 3 millisecond round trip delays. To give you an idea of just how fast that is, the human ear can only recognise delays of 125 milliseconds or greater during a phone conversation. Anything less that 125 milliseconds sounds to us like an instant response.
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 Patch Leads The easiest way to identify faulty patch leads is to replace them. For example, if you are experiencing delays between two computers in particular you may replace the patch lead(s) between the computer and the switch. If the switch is connected to structured cabling, you should also replace the patch between the patch panel and the switch.
2. Faulty Physical Hardware The switch ports that connect computers to switches can sometimes be physically damaged causing intermittent connection problems . The best way to ensure that a switch port is not causing slow LAN performance is to plug the computer into a different switch port. Ensure that the new switch port is on the same VLAN (if VLANS are applied), not shut down and does not have MAC address level security applied to it. If there is a notable difference when attached to the new port then it may be possible you have uncovered a faulty switch port.
3. Over Loaded Switch Switches are made with high throughput in mind, but sometimes the aggregate pressure of many attached computers can cause switches to struggle with performance. This is usually only a problem when the switch has been configured to perform additional functions such as QOS (Quality of Service), VACLs (Vlan Access Lists) or the switch is hosting a large number of VLANS and spanning tree instances. One sign of an over loaded switch is high utilization on the switch CPU.
4. Connected to a Hub Be aware of the difference between a hub and a switch. A switch provides intelligence behind the switching function ensuring that packets are forwarded efficiently. A hub is completely inefficient and forwards every packet out of every port this is a shared Ethernet architecture and it does not scale well with many computers attached or when a large amount of traffic is traversing the hub because every single 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 capacity to run at half duplex for backward compatibility with older equipment such as hubs. When a network interface card is set at half duplex it must send and receive data out of the same wire creating the possibility of collisions between inbound and outbound traffic. Full duplex is the alternative and it is far more efficient using one wire for sending traffic and one for receiving traffic eliminating the problem of Ethernet frame collisions.
