| A Local Area Network(LAN) should have the | | | | 3. Over Loaded Switch – Switches are made |
| capacity to carry a large amount of data with | | | | with high throughput in mind, but sometimes the |
| minimum delay. Even very large corporate LANs | | | | aggregate pressure of many attached computers |
| often have 1 to 3 millisecond round trip delays. To | | | | can cause switches to struggle with performance. |
| give you an idea of just how fast that is, the | | | | This is usually only a problem when the switch has |
| human ear can only recognise delays of 125 | | | | been configured to perform additional functions |
| milliseconds or greater during a phone | | | | such as QOS (Quality of Service), VACLs (Vlan |
| conversation. Anything less that 125 milliseconds | | | | Access Lists) or the switch is hosting a large |
| sounds to us like an instant response. | | | | number of VLANS and spanning tree instances. |
| | | | | One sign of an over loaded switch is high utilization |
| But sometimes the expectations of a high | | | | on the switch CPU. |
| performance LAN are not met. Below are my top | | | | |
| 5 causes of a slow LAN in no particular order. | | | | 4. Connected to a Hub – Be aware of the |
| | | | | difference between a hub and a switch. A switch |
| 1. Faulty Patch Leads – The easiest way to | | | | provides intelligence behind the switching function |
| identify faulty patch leads is to replace them. For | | | | ensuring that packets are forwarded efficiently. A |
| example, if you are experiencing delays between | | | | hub is completely inefficient and forwards every |
| two computers in particular you may replace the | | | | packet out of every port – this is a shared |
| patch lead(s) between the computer and the | | | | Ethernet architecture and it does not scale well |
| switch. If the switch is connected to structured | | | | with many computers attached or when a large |
| cabling, you should also replace the patch between | | | | amount of traffic is traversing the hub because |
| the patch panel and the switch. | | | | every single packet competes for time on the |
| | | | | network with every other packet causing collisions |
| 2. Faulty Physical Hardware – The switch | | | | and retransmissions. |
| ports that connect computers to switches can | | | | |
| sometimes be physically damaged causing | | | | 5. Half Duplex Connections – Modern network |
| intermittent connection problems . The best way | | | | interface cards have the capacity to run at half |
| to ensure that a switch port is not causing slow | | | | duplex for backward compatibility with older |
| LAN performance is to plug the computer into a | | | | equipment such as hubs. When a network |
| different switch port. Ensure that the new switch | | | | interface card is set at half duplex it must send |
| port is on the same VLAN (if VLANS are applied), | | | | and receive data out of the same wire creating |
| not shut down and does not have MAC address | | | | the possibility of collisions between inbound and |
| level security applied to it. If there is a notable | | | | outbound traffic. Full duplex is the alternative and |
| difference when attached to the new port then it | | | | it is far more efficient using one wire for sending |
| may be possible you have uncovered a faulty | | | | traffic and one for receiving traffic eliminating the |
| switch port. | | | | problem of Ethernet frame collisions. |
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