Thursday, July 30, 2009

Getting A Handle On Dropped Packets – 4 Key Troubleshooting Tips

In today’s net-centric environment, organizations often depend on the network for voice over IP, video conferencing and webcasts. Network problems caused by packet loss can create noticeable performance issues.

Is packet loss a problem your organization is experiencing? Could it be contributing to larger problems? One thing’s for sure, almost every network experiences packet loss to one degree or another. Dropped packets can originate in almost any part of the network path, from bad cables to flakey applications. Here are a few common causes and what you can do to fix them:

1 . Find the source. First, understand where the packet loss is occurring. The command line tracer tool helps determine the exact location. Then, learn the extent of the problem by using the “Netstat –s –p tcp” command. This will display the total segments sent and total segments retransmitted. (Check out this site for more information on how to use command line tools)

2. It's probably the cables. More often than not, it’s this simple. Check that nothing has been placed on top of the cable and that the connections are tight. Test by replacing the potentially bad cable with a known good one. Frequently, very long cables will only show excessive problems when they are processing a heavy load.

3. Check for duplex mismatches. Many systems auto negotiate the duplex speed, however errors do occur. Consider manually setting it to a known level and see if the problem goes away.

4. Unleash the routers! If your routers are overwhelmed, they will drop packets. Check for excessive utilization across each link and make sure the system overall is not saturated. Not all routers drop packets at the same traffic level. Some Cisco routers can begin dropping packets at a CPU load of 50%; on other models this may not occur until 95% or more.

Tip for dopplerVUE users: The Locator view lets you sort all interfaces by packet loss so you can isolate the location of dropped packets instantly.


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