Packet Loss: Checking and How to Fix?

Packet loss

Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. It is typically caused by network congestion. Packet loss is measured as a percentage of packets lost with respect to packets sent. Network performance issues are very common as the network is the foundation for the applications and data. Packet loss can be a very bad experience as they travel through multiple devices.

How to check packet loss

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First, you have to check the occurrence of packet loss.

  1. Open a command prompt on a client PC. Search for “cmd” via the Start menu.
  2. Type “ping -n 20”.
  3. This will ping the address 20 times. Substitute with whatever address must be tested to.
  4. Once the command has run, a summary will be presented indicating if the loss occurred.
  5. If no loss occurred, try increasing the “-n” value to something higher (such as 100) to test for a longer period of time.

If packet loss was seen, the next step is to identify where the packet loss begins to occur and then we will see the fix for packet loss. ‘tracert’ can be used to check each layer 3 device along the path to the destination:-

Open a command prompt on a client PC, via the Start Menu, search for “cmd”.

1. Type “tracert -d”.
This will perform a trace route to and present each hop as an IP address. Substitute with whatever address have to be tested.

2. Wait for the trace to complete, or press CTRL+C if multiple lines ending with “Request timed out” are encountered.

A lack of response will be represented by an asterisk (*), potentially indicating packet loss, or that the device is configured to not respond. The test may need to be completed multiple times to identify where loss is occurring. If packet loss is frequently encountered after a particular hop, then the issue most likely is with that device or between it and the previous hop.

It is recommended to test from multiple clients at different locations in the network to help rule out specific client issues and develop generality between clients experiencing the problem.

Causes and how to fix the packet loss

Link Congestion

This occurs when more traffic is attempting to go over a network link than it can support. Such as, 60Mbps of traffic is passing over the same 20Mbps link. This creates congestion, resulting in some packets being dropped. Packet loss can be minimized by,

  • Increase the bandwidth of the congested link(s).
  • Implement Quality of Service (QoS) to give priority to real-time traffic. This will not help the congestion of the link, but it can give priority to applications like voice or video which lowers chances of packets being lost.

Poor/ faulty cable

A cable that has been poorly/incorrectly terminated or damaged can result in an incomplete or inaccurate electrical signal passing between devices. Swapping a cable with a new one or performing a cable test on that particular cable can help eliminate this as a possibility.

Mismatch of duplex

This occurs when two ends of a link are using different speed/duplex settings, such as 100Mbps/half-duplex and 1000Mbps/full-duplex. When this occurs, some or all packets will be lost on the link.

To correct this, ensure both sides of the link have identical settings. Ideally, both ends of the connection should be set to “Auto” for both speed and duplex.

Firewall blocking the traffic

Even if packet loss isn’t occurring for all types of traffic, an upstream firewall may be filtering certain types of traffic. This can result in some websites loading and others failing or some services being accessible, while others are not. If a firewall exists between two devices/locations experiencing these symptoms, ensure that the firewall is not blocking the traffic that is experiencing the problem.

This is the method to check the packet loss. With this, you will get to know if actually there is packet loss and if yes, where the packet loss is occurring. By following the above method, you will get to know ‘How to fix the packet loss’.