SNMP

Almost everyone has heard about SNMP, how convenient and simple it is and how good it is to use it for network monitoring. But not everyone knows what it is and how it works. When I looked around the Internet, I could not find any article that explains what it is in a concise and clear way. That's why I tried to do it myself.

In this article I try to present the possibilities of practical use of SNMP in conjunction with the PHP programming language. The example I have chosen is to get information about the ports/interfaces of the switch. No deep knowledge of either SNMP or PHP is needed to achieve interesting functionality. I think the main thing is the idea (or information) of what we can do.

In the previous article I described how to get basic information about switch ports. A good extension is to add to the port information what VLAN it is assigned to. This operation is not so simple anymore and it depends on the manufacturer of the switch. In this article I describe the procedure for Cisco switches, which should be universal, but is a bit more complicated for higher-end switches. I tested it on Catalyst 2960 and 3750 switches.

In previous articles I described how to find out basic information about the ports on the switch. And how to complete the information by assigning the port to a VLAN. In this episode, I'll cover another interesting extension, finding out the MAC address of the device that is connected to the port. This can come in handy in a number of situations, for example a computer starts communicating on our network and we need to find out where it is physically located. I tested the procedure on Cisco Catalyst 2960, 3750, 6500 switches, but it should be applicable to other brands as well.

Having found the MAC addresses of the devices that are connected to the ports of the switch, it would be useful to supplement these MAC addresses with the corresponding IP addresses, which will tell us more about the device. If we have a central router (switch) in the network through which individual computers communicate (on L3), we can download its ARP table and that's it.