Troubleshooting WAN Issues – CompTIA Network+ N10-006 – 4.8

WAN connections can have signal problems, routing protocol issues, and other challenges. In this video, you’ll learn about troubleshooting interface issues, latency problems, routing table issues, and more.
<< Previous: Troubleshooting Authentication IssuesNext: Troubleshooting Customer Premise Equipment >>

On your local area network, you have complete control over the physical plant. If someone is having a problem with a bad cable, you simply swap the cable out or you recrimp the ends and you’re up and running again. But the wide area network cables are completely outside of your control. The WAN provider is responsible for keeping the wide area network up and running, and very often construction or other things in your environment might break the link between you and that remote wide area network location.

If you feel that there is some type of hardware problem, the wide area network provider can loopback one of the connections, usually at the interface inside of your environment, and they can test to see what the experience is like sending traffic to your location and having it loopback to the provider. They can then see if they’re receiving the same information back and determine if that line is working well or not. Then you can start troubleshooting even further to determine is the problem with an interface inside of our building or cables between the wide area network point of presence and our equipment inside of our location?

If you’re running copper cables to get to this wide area network, you can certainly have examples of interference, especially inside of a building where we have so much electrical equipment and other devices that can cause RF interference. And if you’re communicating over a non-terrestrial link for your wide area network, that means that you are leaving the earth and going up to a satellite in space and being bounced back down again. And that process takes time to get up to the satellite and back down to the remote site. And then, of course, the response has to go back up to space and back down to you again.

So if you’re working with an application that does not handle latency very well, then you probably don’t want to put it over a non-terrestrial link. If the wide area network connection is working the way it should, you could still have problems with the configuration of the protocols that are going over that wide area network. A good example of this is split horizon. This is a configuration you would set in the dynamic routing protocols that you’re using across this wide area network link. This is ideally designed to prevent any type of routing loop on the network.

On a dynamically routed network, a router is going to advertise all of the routes that it knows to all of the other routers that are directly connected to it. These routes are going to be set periodically and you’re going to constantly make sure that everybody’s aware of all the routes that your router happens to know about. With split horizon, the router determines what routes have been learned over a particular interface, and it chooses not to advertise those routes back out to that location. That location already knows about the routes, and you’re able to conserve wide area network bandwidth by not sending a duplicate of those routes to a location that already knows that those routes exist.

Another important configuration concern is with our domain name system servers. These DNS servers are there so we can reference devices by their name rather than having to memorize an IP address for every single device on the network. Well, of course, that’s a very important process. It’s one of the first things that happens when you’re trying to communicate to another device is to resolve the IP address from the name that you’re providing, and it’s these DNS servers that provide that for us.

If a DNS server stops responding to us then we’re no longer able to resolve the IP address and therefore, cannot communicate to that other device. If the DNS server slows down, you may try to begin a communication but it takes a number of seconds to finally resolve the IP address, and then the process can continue. And that slight delay can slow things up for everyone. The idea in most environments is that you would have multiple DNS servers and you would be able to share the load and maintain the uptime across multiple DNS devices.

On your router and wide area network devices themselves, we also have to be very aware of how they’re configured for WAN speeds and make sure that they match on both sides of the connection. And, of course, the routing table in our wide area network routers is very important since that determines how we’re going to transfer information from one side of the network to the other.