Probe request

As explained in Acing the CCNA Exam: Volume 2 Advanced Networking and Security

A probe request is an 802.11 management frame that a wireless client transmits to discover nearby access points and the service set identifiers they advertise.

A probe request is an 802.11 management frame a wireless client sends to discover nearby access points and the SSIDs they advertise. The exchange supports the client association process: after discovery, the client authenticates and associates before sending or receiving wireless data. section 19.1.2 section 19.3

Clients discover access points in two ways:

• Active scanning sends probe requests and listens for probe responses; it discovers access points quickly but can reduce battery life. section 19.1.2
• Passive scanning listens for periodic beacon messages advertising each BSS; it conserves battery life but may discover networks more slowly. section 19.1.2
• Discovery is followed by an authentication request and, if successful, an association request. section 19.3

Figure 19.3 The client association process. The probe request/response exchange allows PC1 to discover AP1. PC1 then authenticates and associates with AP1.

Trace the probe request and response exchange that lets a client discover an access point before authentication and association. section 19.1.2

How Acing the CCNA Exam: Volume 2 Advanced Networking and Security covers it

How deep it goes

Defines active and passive discovery and their trade-offs, but stops short of probe-frame field-level implementation.

Examples

Uses a phone or laptop discovering café and household SSIDs as a familiar active- or passive-scanning experience.

What you can do after

Evaluate how a wireless client discovers access points and distinguish active scanning from passive scanning.

How it connects

Connects active scanning with probe responses, passive scanning with beacons, and discovery with authentication and association.

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Related concepts

• active scanningused by · Active scanning is a wireless discovery technique in which a client sends probe requests and listens for probe responses from nearby access points.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 2 Advanced Networking and Security. The section links point to the parts of the book it draws on.