Bssid là gì

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The terms BSSID, ESSID, and SSID are all used to describesections of a wireless network (WLAN)—the three terms have slightlydifferent meanings. As a wireless user you are concerned only withthe broadcast SSIDs that let you connect to a wireless network. Asan administrator, you also need to keep track of BSSIDs and, to alesser degree, ESSIDs.

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An SSID is the Name of a Network

Because multiple WLANs can coexist in one airspace, each WLANneeds a unique name—this name is the service set ID (SSID) ofthe network. Your wireless device can see the SSIDs for all availablenetworks—therefore, when you click a wireless icon, the SSIDsrecognized by device are listed. For example, suppose your wirelesslist consists of three SSIDs named Student, Faculty, and Voice. Thismeans that an administrator has created three WLAN Service profilesand, as part of each WLAN service profile, provided the SSID nameStudent, Faculty, or Voice. (For directions to create a WLAN Serviceprofile, see Creating and Managing a WLAN Service Profile.)

Figure 1: Radios can have up to 32 SSIDs
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As a WLAN user, you are concerned only with the SSIDs. You selectone from the list on your laptop or other device, provide your usernameand a password, and use the SSID. You might not have access to allSSIDs—the authentication and access privileges are usually differentfor different WLANs and their associated SSIDs.

BSSIDs Identify Access Points and Their Clients

Packets bound for devices within the WLAN need to go to thecorrect destination. The SSID keeps the packets within the correctWLAN, even when overlapping WLANs are present. However, there areusually multiple access points within each WLAN, and there has tobe a way to identify those access points and their associated clients.This identifier is called a basic service set identifier (BSSID) andis included in all wireless packets.

Figure 2: Each Access Point has its Own BSS
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As a user, you are usually unaware of which basic service set(BSS) you currently belong to. When you physically move your laptopfrom one room to another, the BSS you use can change because you movedfrom the area covered by one access point to the area covered by anotheraccess point, but this does not affect the connectivity of your laptop.

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As an administrator, you are interested in the activity withineach BSS. This tells you what areas of the network might be overloaded,and it helps you locate a particular client. By convention, an accesspoint’s MAC address is used as the ID of a BSS (BSSID). Therefore,if you know the MAC address, you know the BSSID—and, becauseall packets contain the originator’s BSSID, you can trace apacket. This works fine for an access point with one radio and oneWLAN configured.

Most often, there are different BSSIDs on an access point foreach WLAN configured on a radio. If you have an access point with2 radios and 32 WLANs configured on each, you would have 64 BSSIDsplus the base access point BSSID. To accommodate the multiple BSSIDs,each access point is assigned a unique block of 64 MAC addresses.Each radio has 32 MAC addresses and supports up to 32 service setidentifiers (SSIDs), with one MAC address assigned to each SSID asa basic service set identification (BSSID). All MAC addresses foran access point are assigned based on the base MAC address of theaccess point.

Note

The access point MAC address block is listed on a label on theback of the access point.

To view a list of SSIDs for a network, look at the list of WLANService Profiles in Network Director.

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Ad-Hoc Networks Do Not Have a MAC Address

Every BSS needs a BSSID, and using the access point’sMAC address works fine most of the time. However, an ad-hoc network,a network that forwards traffic from node to node, has no access point.When a BSS does not have a physical access point, in an ad-hoc networkfor example, the network generates a 48-bit string of numbers thatlooks and functions just like a MAC address, and that BSSID goes inevery packet.

An ESS Consists of BSSs

An extended basic service set (ESS) consists of all of the BSSsin the network. For all practical purposes, the ESSID identifies thesame network as the SSID does. The term SSID is used most often.