PacketTrap pt360 Tool Suite is a free and very helpful piece network diagnostic software.
It has all sorts of tools. These tools include a switch port mapper, a MAC scanner, an SNMP scanner, and even a TFTP server.
The easiest way to get the software is to do a Google search for PacketTrap pt360 ToolSuite Pro. Once you install it it will ask you for a username/password or to create an account for the license. Don't worry, it is free and once you get signed up, they will give a license that is good for about 30 years.