What is most likely to cause packet loss?

[InlineFive]

A computer at work is having pretty bad packet loss. Typically I think the network cable is the fault of this. I tested the network card and the switch is brand-new and working.

Am I on the right track to replace the cable?

-Por

 

[spidey07]

Cable problems are the number one cause of errors and packet loss.

Taking the computer to a known good network jack will tell you if its the PC.

If it isn't the PC/NIC then its the cable. If not the cable then the port on the switch.

 

[InlineFive]

Originally posted by: spidey07
Cable problems are the number one cause of errors and packet loss.

Taking the computer to a known good network jack will tell you if its the PC.

If it isn't the PC/NIC then its the cable. If not the cable then the port on the switch.

Thanks for the quick response spidey07. I appreciate it.

 

[Garion]

Another common cause is a speed/duplex mismatch between the switch and the PC. One thinks that it's full duplex and one that it's half. The half duplex end sees collisions on the wire when there aren't any and the full duplex end sees packet errors because there are collisions on the wire and there shouldn't be.

- G

 

[InlineFive]

Both are set to auto. In any case, I can't configure the switch end of things.

 

[Garion]

How are you seeing packet loss? From where to where? Are you seeing it from your PC to your router, or is it across the Internet?

If it's across the Internet, it's typically caused by congestion somewhere out there - Too much bandwidth trying to squeeze into too small of a pipe. It might also be caused by congestion in your local segment - Cable modems are more prone to this than DSL networks, however.

- G

 

[fs5]

Originally posted by: PorBleemo
A computer at work is having pretty bad packet loss. Typically I think the network cable is the fault of this. I tested the network card and the switch is brand-new and working.

Am I on the right track to replace the cable?

-Por

Try running ethereal on the comp and seeing what types of packets are going out. Look for worm/virus activity... (sequential port scans, 1000's of packets going out at once, etc etc)

 

[InlineFive]

Originally posted by: Garion
How are you seeing packet loss? From where to where? Are you seeing it from your PC to your router, or is it across the Internet?

If it's across the Internet, it's typically caused by congestion somewhere out there - Too much bandwidth trying to squeeze into too small of a pipe. It might also be caused by congestion in your local segment - Cable modems are more prone to this than DSL networks, however.

- G

Across the network from the computer to our firewall. Using ping as it's the best tool I know of for that.

 

[ScottMac]

Congestion is also a frequent contributing factor to packet loss on a WAN.

If some part of the path is backed up / causing a severe bottleneck, the packets can time-out in transit and be dropped.

If you haven't already (and you're using a "commercial grade router" that supports it) make sure you have traffic shaping enabled.

Traffic shaping will pace the traffic onto the pipe to reduce congestion.

If it's on the LAN, there may be an issue with the PC itself, the NIC, and / or the drivers. If the PC is "busy" (bring up the task manager and see what the CPU / memory utilization is), it may not be able to process the traffic in a timely fashion.

If you think it's the PC, I'd vote for a NIC / Driver issue (especially if it's a built-in NIC).

Good Luck

Scott

 

[Garion]

Originally posted by: PorBleemo

Originally posted by: Garion
How are you seeing packet loss? From where to where? Are you seeing it from your PC to your router, or is it across the Internet?

If it's across the Internet, it's typically caused by congestion somewhere out there - Too much bandwidth trying to squeeze into too small of a pipe. It might also be caused by congestion in your local segment - Cable modems are more prone to this than DSL networks, however.

- G

Across the network from the computer to our firewall. Using ping as it's the best tool I know of for that.

If you're seeing packet loss across a LAN, you have a few possible culprits:

Bad cabling
Bad speed/duplex negotiation
Bad NIC
Bad switch port
Interferece on the wire (i.e., florescent lights, etc.)

Work on the variables - Try a different PC, try a different switch port, try that PC on a different cable that's known to be good, etc.

One note - Many PC NIC drivers hide a lot of L2 errors from the stack - You might be seeing a lot of errors and not know about.

Also, different kind of errors mean different things. What are you seeing? FCS, CRC, collisions, runts, giants, etc?

- G