Network Monitoring And Management
Network Peformance Problems
By Michael Griffin
One of the top causes of slow network devices are Auto Negotiation issues. Assumptions about how auto-negotiation works often lead to a wrong setup. Auto-negotiation allows a router or switch port to automatically connect with a device and determine the optimum duplex and speed for that device.
Speed is the transfer rate of the interface 10Mbps, 100Mbps, 1000Mbps, etc. Duplex describes how data flows on the interface. With Half-duplex data flows only one direction: data can only be transmitted or received but not both. Full duplex allows both transmit and receive to happen simultaneously. Half duplex is like a walkie-talkie whereas full duplex is more like a phone conversation where both parties can talk at the same time.
Auto negotiation does not determine the port settings on the other end of the line but rather starts a dialog with the connected device. If both ends are set to auto then a successful, high speed connection will be negotiated. If one end has been set to fixed settings for speed or duplex then auto-negotiate will fail and the connection settings may differ and the connection speed will suffer.
MTD Best Practice: if both ends of the link support Auto-Negotiation then use it, otherwise be sure to set both ends to the same settings.
If network Ethernet wiring or the Fiber is not made correctly, then the port may receive too many errors. It may (depending on the settings) auto-negotiate a slower speed. We have seen bad gigabit fiber slow to a crawl when the fiber was poorly made, poorly run, cracked because it took a turn too sharply, cracked because it was tugged too hard, or when the transceiver module on one end or the other went bad.
With standard twisted pair Ethernet care must be taken to use a properly rated cable with good ends particularly at the higher speeds in or again the speed will fall and you will not get the performance you expect. Be cautious when you just pull a cable out of the pile to make that connection. Do you really know that it is speced for 1000BT? If it's fiber, is it really good?
Fiber and Ethernet testers from companies such as Fluke should be used particularly in large installations to verify cable integrity. But once the system is in place, how do you know when something like this is happening? A simple ping test is great to see when there is an outright failure but will not help locate these kinds of problems. Looking at throughput, errors, and packet loss on a switch port may be the best thing to look at if there is a slow down and you've ruled out problems such as auto-negotiate.
Many network switches have a web interface that allows you to check the status of ports. If you are using Cisco and most professional switches, the 'show interfaces' command from the console login will show a variety of stats about the port including the various errors so you can confirm connections. MTD Systems can monitor port throughput and status over time to give easy visibility to these kinds of problems.
MTD Best Practice: Confirm network integrity by checking throughput by transferring large files while also watching for CRC errors and dropped packets. Deficiencies in any of these parameters may mean a faulty cable which should be checked with a cable tester or an auto-negotiation issue.
MTD Systems is a network systems monitoring company with products optimized for video based systems like newsroom, transmitters, Digital Cinema, and satellite distribution. You can also see the MTD blog here.
Mike Griffin is Chief Technology Officer for MTD Systems.
Article Source: http://EzineArticles.com/?expert=Michael_Griffin
