5 Considerations for Network Connection Problems

Errol explains five factors to consider if you're having network connection problems, between switch to switch or between transceiver and transceiver (GBIC/SFP).


Hi. Thank you for joining us today. My name is Errol and today I am going to discuss the top five reasons why you may be having issues with a connection from switch to switch, transceiver to transceiver and so on like that.

So let us get into it. As most people know, most of the problems with connections and network are found at the physical layer, layer one.

The first thing you have to do is check your physical connection. The easiest to do is to pull the cable out, receive it back in. If you have a transceiver, or GBIC or SFP, whatever you want to call it. Pull that out, push it back it. To the cable, pull it out, push it back it. Do that on both ends. Make sure you have a firm, solid connection.

The next thing you do is, back in the days when you are in science class, doing a science project, you always want to create the causes so you try to find out what your variable is in your changes.

So what I recommend doing if you are not getting connection, try non-working things such as a cable. If you are not getting a connection, try different cable. See if you get a connection. If you do get a connection, then the cable is probably bad. If you do not get a connection, try the next thing.

Try to go to a non-working port on the switch. Let us try this port. If that works, then you know you had a bad port. If it still does not, then maybe it is something else.

If you are working with fiber and you have a transceiver or GBIC, then what you want to do is try a non-working one if you have one. And if all that still does not work, then also try a whole different switch because maybe the switch itself could be bad.

Okay, so now we are coming to number three, distance. Make sure the distance that you are using matches the technology that you are using. Usually, with copper, twisted pair, goes to about a hundred meters. If you are going over that, you probably going to start losing connection. It's probably not going to work.

Couple common fiber ones are multi-mode which is 220 meters or 550 depending on the micron that you are using and in single-mode usually is about 10 kilometers. Make sure you are not going over those.

Next thing I would say is, make sure you have the correct product. Is it the same interface on both ends? Do you have a multi-mode SFP transceiver on one end and then LX on the other hand. Simple things but sometimes, it is the thing that track and that is what is going on.

Is it supported? Do you have the right SFP in there? Do you have an HP SFP in a Cisco switch? That really does not work too well.

And sometimes, you may even need to upgrade. Maybe it is supported but you have the wrong version of firmware so you may have to upgrade the firmware and maybe it does not accept SFP just because the HP SFP maybe does not work in legacy equipment and you may have to upgrade to a more advanced product.

Finally, number five, which is actually the most broadest subject, is the configuration. What you want to do is make sure your configuration is correct. The ports turn off because you can disable ports and you may not know that they are disabled. Maybe they were disabled in a previous configuration.

Auto-negotiation, this is a big one sometimes. Sometimes you are going from a different manufacturer. Maybe from a Cisco to an HP or even from an Avaya to Avaya but with different switches, what can happen is auto-negotiation can be turned on on one side and off on the other side, so they are not talking correctly.

So what you want to do is try four different things. Try turning it on on both sides, then try turning it off on both sides. Then maybe turn on on one side, off on the other. And the switch it off on one, and on on the other. Sometimes usually it is weird but that part works.

Span entries is another one. Span entry can get a little difficult, complex sometimes, but make sure there is not a loop on the system. Usually if there's a loop you'll see a bunch of life just flickering up blinking like a Christmas tree. But maybe span entry shut down one of the ports and maybe that is why you are not getting a connection.

And actually, for this third bullet are the shared ports. This I am going to actually show you an actual switch so you can see what I am talking about.

For the last thing, what I want to discuss was shared ports. Sometimes, you call them shared ports, sometimes they call the borrowed ports. But what it is is, if you look at this switch, you have ports one through 24 and there are these two SFP ports, you see this little ring around it.

Basically means you can only use one or the other. So maybe if you have something plugged in here, this will not be working. Or vice versa, if you have something plugged in here, this one will not work. So the connection will not work. You can only use one of the other.

So that is one thing that you want to check to make sure that that is working properly and that you do not have something plugged on both ports so that way, you can get a connection.

So thank you for joining us today. Hopefully this helps you out with your connection issues. Thank you for joining us and I will see you next time.