Troubleshooting Interface Configurations – CompTIA Network+ N10-006 – 4.6

| May 11, 2015


A network interface has many different configuration options that can have an impact on network performance. On this video, you’ll learn about network interface configuration problems and how to troubleshoot interfaces.
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If you’re suffering from an interface configuration issue, then you might see symptoms like these. You could certainly see very poor throughput. You’re transferring a file and it’s not transferring very quickly. Or as you’re surfing around the net, you’re noticing a very consistent and very low throughput.

Perhaps you look at your interface card, and you’ll notice there’s no link light at all. You have no connectivity to the network. And you’re not able to see any signal or any lights turned on on your network interface card. Perhaps the light is blinking, or you can see that the light is solid, but you’re not getting any information sent out over the network. If any of these things are occurring, you might have a configuration problem with the interface card itself.

If you look at all of the different configuration options for your network interface card, you might be surprised at how many things you can change or modify with the configuration of that card. Let’s look at some of the more important configuration settings that you could have in that interface.

One is to set the automatic or manual configuration of the interface itself. Instead of manually setting speed and duplex for the card, you can have the card automatically check to see what type of network it’s connected to and set its speed and duplex automatically based on that information.

Most of the time this process works perfectly. You plug into the network. And it automatically finds the speed and duplex. And everything is working exactly the way it should. But occasionally the devices do not sync up properly on each side. And one device will configure itself incorrectly. And now you’re running at the wrong speed or a different duplex. And that will certainly cause performance problems across the network.

You might also want to check the lights on your network interface card. There’s often at least a signal light that tells you you have a connection back to a switch. And there’s also usually a light that flashes that tells you if data happens to be going through that connection.

If there’s no light on that connection side, then you want to check the cable or the connection off to the switch that you should be connecting to. If there are no lights appearing on the card itself, you may want to check to see if the card is working properly or if it’s receiving power from the device.

One reason that light may not be turning on is that the speed setting on both sides is mismatched. You might have one side set to Gigabit and the other side set to 100 Megabit. And that will cause the connection to never light up. You’ll never get signal between those two devices. And you won’t see any lights appear on the network interface card.

If the duplex is mismatched between two devices, you’ll have performance problems. So you’ll want to check to see what one side of the connection is set to and make sure the other side of the connection matches that setting. Most devices these days are configured as full duplex. But if you happen to have a switch configured as half duplex and you connect to it at full duplex, you’ll find that your network performance will suffer across that connection.

Your problem might also be with the switch configuration. If the interface you’re connecting to has been assigned to the incorrect VLAN, you’ll be able to connect to the network, you’ll get a link light, you’ll be able to send information, but unfortunately you’ll not be able to have any communication outside of that local subnet.

If you look into the details in your operating system or on a switch or router or other networking device, you’ll often find a number of statistics associated with the network interface. This is one that’s on my switch. It shows me a port. It shows me the number of unicast, multicast, and broadcast packets, in and out. And it shows me the number of octets, in and out.

And right underneath that, it shows me all of the different errors that could be occurring across that link. So you can monitor the interface and see if any of these error counters are increasing. And if they are, you may be having some type of communication problem between the switch and the other device.

You might also want to confirm what the speed, the duplex, the VLAN settings, and all of the other configuration options might be for that interface and make sure that it matches the device on the other side. Then you can start performing some two-way traffic communication. See if you can communicate to other devices on your local subnet. See if you can communicate to your default gateway. And then try some communication out to the internet.

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Category: CompTIA Network+ N10-006

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