Networking / Beginners

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BSSID, SSID, and ESSID

Wireless devices connected together into a network, whether ad hoc or infrastructure, require some way to identify that network. Packets bound for computers within the network need to go where they're supposed to go, even when you have more than one Wi-Fi network overlapping. The jargon gets a little crazy here, especially because marketing has come into the mix.

The Basic Service Set Identifier (BSSID) defines the most basic infrastructure mode network, a BSS of one WAP and one or more wireless nodes. With such a simple network, the Wi-Fi folks didn't see any reason to create some new numbering or naming scheme, so they made the BSSID the same as the MAC address for the WAP. Simple! Ah, but what to do about ad-hoc networks that don't have a WAP? The nodes that connect in an IBSS randomly generate a 48-bit string of numbers that looks and functions just like a MAC address, and that BSSID goes in every packet.

You could, if required, discover the MAC address for the WAP in a BSS and manually type that into the network name field when setting up a wireless computer. But that brings up two problems. First, people don't want to remember strings of 48 digits, even if translated out as six hexadecimal octets, like A9-45-F2-3E-CA-12. People want names. Second, how do you connect two or more computers together into an IBSS when the BSSID has to be randomly generated?

The Wi-Fi folks created another level of naming called a Service Set Identifier (SSID), a standard name applied to the BSS or IBSS to help connection happen. The SSID- sometimes called a network name-is a 32-bit identification string that's inserted into the header of each data packet processed by a WAP. Every Wi-Fi device must share the same SSID to communicate in a single network.

So let's take it one step further into a Wi-Fi network that has multiple WAPs, an ESS. How do you determine the network name at this level? You simply repurpose the SSID, only apply it to the ESS as an Extended Service Set Identifier (ESSID).

Unfortunately, most Wi-Fi devices just use the term SSID, not ESSID. When you configure a wireless device to connect to an ESS, you're technically using the ESSID rather than just the SSID, but the manufacturer often has tried to make it simple for you by using only the term SSID.

TIP The CompTIA Network+ certification exam uses the two terms-SSID and ESSID-interchangeably. Concentrate on these two terms for the exam.