When you have a working vSwitch in your environment, chances are you’re going to want to make sure that you can participate in one of a few different monitoring methods to determine the complex topology of switches. We sometimes refer to this as the “neighborhood” of switching.
Most switches are connected to at least one other switch, forming a web of switches that can all talk to one another. Using a discovery protocol, we can allow these switches, both physical and virtual, to understand who their neighbors are.
Cisco Discovery Protocol (CDP)
The VMware standard vSwitch supports only one single protocol for discovery, the Cisco Discovery Protocol. Can you guess which switch manufacturer uses this protocol? We’ll give you a hint—it’s not Brocade.
CDP is a proprietary way to allow switches to chat with one another to figure out who they are plugged into. It’s not required for traffic to flow, but it does give administrators and engineers a great way to see what device is at the end of a plugged-in port. It also updates itself in real time, meaning it has a lot more value than trying to keep your configuration in a spreadsheet or some other manual method. CDP is enabled by default on Standard Switches. Figure 8.5 shows the output of the show cdp neighbors command on a 3550 switch to which a Standard Switch has been connected.
Figure 8.5 CDP information on a Cisco 3550 switch connected to two vSwitch uplink ports