Today, I was on a 4-hour support call assisting a seasoned “IT Guy” and a fairly green reseller with a remote installation. I was astonished with the number of issues that “came up” and were simply resolved by identifying the MAC address of the access point.
Fun Fact: “MAC” stands for Media Access Control and is a unique address assigned to every piece of network-connected gear. This is how network traffic is able to find its destination.
ISSUE #1 – The MAC addresses were not identifiable on the physical APs or a network topology.
This issue led to many other sub-problems. Seeing as every piece of network gear between the AP and the controller tracks the MAC address, it is THE single most important piece of information you will need when troubleshooting connectivity issues. If an AP isn’t connecting to the controller, how would you identify THAT particular AP from the others?
If you said by the MAC address, give yourself a gold star for this round.
Make it a practice to label the APs with the corresponding MAC address so it is visible AS you deploy. You will also want to create a floorplan which clearly shows the location of the AP and has the MAC address labeled.
ISSUE #2 – The MAC of the problematic AP wasn’t immediately identifiable.
Clearly, this issue stems from the first. Luckily in this case, the partner was able to identify which cables were ran to the corresponding ports on the Ethernet switch. Did you know that every managed switch typically has a visible table of port numbers and MAC addresses? We were able to retrieve this information and then determine which MAC address was communicating with that port.
Boom. Complete list of AP locations with MAC addresses.
MORE POINTS TO PONDER
Know how to read a MAC address. Why is this useful? The first few characters of the MAC address identify the vendor. This makes it easy to look at a table of MAC addresses and understand which components you are looking for.
Or perhaps you are trying to track down a device and you have no idea what you are looking for. The MAC address can be reverse searched on the internet and let you know the manufacture for sure, and sometimes even be as specific as the type of device that it is registered to.
Finally, if you are looking for a specific device on the network, knowing that the last 4 characters are typically unique in a single deployment will save you the time and trouble of trying to remember every character in the MAC address. Just grab the last four and scan any logs or tables for those characters. When you find them, validate the remaining characters just to make sure it is the correct device.
Know how to convert the IP address into a MAC address. In one case, we could not connect to the problematic access point. We tried all the typical methods with no success. However, it would respond to a ping. So it came to a point that I wanted to verify that I was actually talking to a Samsung AP. A ping response simply tells me that “something” is out there talking back to me. I assumed it was a Samsung AP, but to be sure, I wanted to see what MAC address was associated to the IP address that I was pinging. On a LAN, typically, each MAC address will be mapped to one IP address. In windows this can be discovered by looking at the arp table that shows the association between MACs and IP addresses. This is done by simply typing arp -a at the command prompt.
From this table I could clearly see the device I was talking to, that I assumed was a Samsung AP was not at all. [Review Point 3 to see how MACs are associated to vendors] This explained why all the methods I used to try to connect to it would not work. It wasn’t the device I thought it was.
In summary, understanding that the MAC address is used in every single network device between the Samsung AP and the controller will save you many hours of troubleshooting. It is important to understand how to break down a MAC address and how to convert an IP address to a MAC address. It is also important to become familiar with your different network components to understand how to extract the information you are looking for. If you operate on the theory that you know the information is in there and you only need to know how to get it out, a quick Google search can help.
These tips and tricks were very helpful in resolving several different issues all layered on top of each other. I assumed this was common knowledge with IT professionals, but I learned today that it was not.