Common Layer 1 Issues

Common Network Problems

We're going to be talking about some common problems that we see on our layer 1 networks, and then we're going to talk about some common causes for those, and then also some cable considerations when you're dealing with your different networks.

So first up, let's talk about some common network problems. Here I have a network, and let's say I'm on this PC right here. The first thing is maybe it doesn't have any connectivity at all. Maybe it just flat out doesn't have connectivity. Maybe it's because it's not plugged in, or maybe because the port on the switch has gone bad and so now that port no longer works, or maybe there's some patch panel cables that are missing, patch cables. So there's a whole host of reasons, but maybe this machine doesn't have any connectivity at all.

Or maybe it does have connectivity, it just can't reach much of anything on the network. So maybe it's not capable of reaching something on its own network, or maybe it's trying to reach something on a remote network. Maybe it can reach its local devices, it just can't reach this machine over here. So you don't have end-to-end connectivity between these two devices. Something's gone wrong. It could be because this network is not seen over there, or it could be because one of these connections is down.

Or even worse yet, maybe you have intermittent issues. Maybe this connection is going up and down. We call that flapping. So the network connection goes up and then it goes down, and it causes it where you're not able to have that end-to-end connectivity. Or maybe what's happening is the packets are making it to here and they drop when this goes down, but then it goes this direction, and so that works for a little bit, and this is flapping in and out, so it gets confused on which direction is it heading. So that could be something that a flapping interface would cause all sorts of problems with.

There's also could be performance issues. So this might not stop that end-to-end connectivity. Maybe it still has end-to-end connectivity, and maybe that flapping doesn't cause intermittent connectivity issues, but maybe it's causing some sort of performance issues, and that can affect the speed of the connection that you're going from one location to another. Or it could cause something called latency, which just stops these packets from getting over from one location to the other location in an expedited manner. So maybe it's just too much delay, and you have too much delay between these two devices.

Perhaps you have something called jitter on here. And what jitter is is it can communicate just fine some of the time and not other points in time. And so you've got kind of this where packets will get in and then it'll stop getting in and then it'll get in, and so you'll have a big delay and then little delay and then big delay. And so that's jitter, where you're just getting that inconsistency with it. So those are some common problems with connectivity on the layer 1 level.

Common Causes

So let's take a look at some of the common issues you may see on your network. The first one we'll talk about you may not even have control over, because that's through your internet service provider or some sort of service issue. So you are going to subscribe to certain services, and perhaps that's your internet service provider that's providing connection to the outside world, or maybe you have some sort of leased lines that are going in between your sites, and so you have some sort of service issue with there. In fact, I've had some sites where the backhoe digs up one of the fiber lines and they lose connectivity for a day or two. So one of the common issues that you'll have is just some sort of service issue with some sort of service provider, like your internet service provider.

There are also cabling issues that you can encounter. For instance, maybe you have some sort of incorrect pinout on the different ends that you have, or maybe the connection was not strong enough and has come apart, and so now you don't have a strong connection. If your cables are running too far, maybe you have some sort of attenuation. If there's like a big twist in your line or a knot in your line, that can affect that attenuation as well. Or perhaps you have some sort of noise or interference, that these cables are running by power, or cables are too close together, or something that's going to cause some sort of interference. Or maybe there's some sort of short. Maybe those cables broke apart and it created some sort of open circuit that's not communicating anymore, or some sort of the insulation has gone away and rubbed away and now it's touching something and grounding out and you've got some sort of short. Or perhaps it's fiber optics that are connected together but it had a little dirt or dust or something in there that now it's not making a clean connection. So those are some of the cabling issues that you can encounter.

There are also resourcing issues. This is inside of a switch, and we see that there's components here inside the switch that do processing, and there's RAM inside of these switches. And so there's different things that can become overwhelmed with traffic. And so maybe you spike the CPU on these different switches, or you spike how much RAM or the buffering on these devices. And so there's different limitations to these devices, and you could be hitting those resource limitations.

Or perhaps your equipment goes offline. So here are some switches here, and I've quite often will see where the power will go out, and the power goes out either going to the device, or your device has some sort of power supply on it and sometimes I've seen that busted where it's not working anymore. So that can be a problem, the equipment itself. I've seen hardware just fail, just flat out fail, and I've had to switch out hardware before. I've seen cabling faults, especially with cables that are made by somebody rather than purchased, like patch cables that somebody has made, and I've seen those go bad. But I have seen other cables go bad as well.

I've also seen ports go bad. There are specific ports on those switches that I've seen. The first time, I actually had a really hard, I tested it many, many times to make sure I was actually seeing it correctly: a Cisco switch with a port out. I've had other brands do it quite often, but Cisco, that seems pretty rare to happen. So I tested it multiple times, and in fact the port had just gone bad. And then also, maybe rather than just being completely down, maybe you get some sort of errors during that communication. So the fault creates just kind of errors rather than just being disconnected altogether.

I mentioned with troubleshooting that sometimes what will happen is there'll be configuration errors, and so this is one of the most common type of errors that there are, where things will be misconfigured so something goes down. So I see things like interface configuration errors. When you're in these switches, sometimes you're configuring that interface, and I've seen wrong things like wrong VLANs entered into there. I've seen mismatched duplex, so one's half duplex and the other one's full duplex, and mismatched speeds. We don't encounter as much anymore with a mismatched duplex and mismatched speeds, because those are usually on older equipment that we had those issues. But you could potentially still see that. Or maybe it's an interface on a router that there is no IP address that was configured on it. Or maybe it was configured with the wrong IP address or the wrong subnet mask. Or maybe the piece of equipment doesn't have DNS and it's trying to do some sort of DNS resolution. Or in this case, some of these switches will have transceivers, and maybe you put the wrong transceiver inside of those. So there's a lot of configurations that we can program wrong on these devices and set up wrong. And like I say, that's one of the most common issues that you have on your networks.

Cable Considerations

There's lots of different reasons. I'm not going to get real in depth into this because I covered some of this earlier, but there are things like with your Ethernet cables, you can have a shielding that goes along with this to keep it from having interference with other devices. So that's one thing.

One thing we didn't talk about is there's also something called a plenum cable. And what it is is the plastic that they use is non-toxic if it were to be burned. And so if you are going up into like a false ceiling that has, you know, some sort of ventilation and stuff in it, then it needs to be a plenum cable. So that way if there is a fire, it's not going to cause a bunch of toxic fumes to go into the office. So that's one consideration.

Also, if you're having problems with, maybe shielding is not the best to shield you from other devices and other interferences that you're getting, maybe at that point in time you want to go with fiber and run fibers. And then this here's a cable with some shielding as well. So there are different reasons why we choose different cables and different types of cables with it, and different considerations for different applications.