CompTIA Exam Prep - ITF+, A+, Network+, Security+, CySA+

A toner and probe — also called a tone generator and inductive probe , or informally a fox and hound — is the tool you reach for when a cable disappears into a wall at one end and you need to find which of two hundred unlabelled cables in a patch panel is the other end. The toner injects an audible tone onto the cable. The probe finds it by induction, without touching the conductors. It is the answer to one very specific exam question — "how do you identify an unlabelled cable?" — and a genuinely common piece of field work. How It Works The tone generator clips onto or plugs into the cable at one end and injects a low-frequency signal, typically a warbling audio tone. The inductive probe is swept near the suspected cables at the other end. It picks up the electromagnetic field produced by that signal and converts it back to audible sound through a small speaker. The cable carrying the tone is loudest. The word inductive matters: the probe does not need electri...

A machine showing an IP address starting 169.254 has told you something precise: it asked for an address and nobody answered. That is an APIPA address — Automatic Private IP Addressing — and it is one of the most diagnostically useful things you can see in ipconfig output. 169.254.x.x means the DHCP request went unanswered. The address is the symptom; the DHCP path is the problem. Windows calls it APIPA. The vendor-neutral term is link-local addressing , defined in RFC 3927, and macOS and Linux do the same thing. The full range is 169.254.0.0/16 , though the first and last 256 addresses are reserved, so hosts self-assign from 169.254.1.0 to 169.254.254.255. What the Host Actually Did When DHCP fails, the host picks an address from that range at random, uses ARP to check nothing else is already using it, and assigns it. If there is a conflict it picks again. The consequence is the part people miss: it assigns an address and a subnet mask of 255.255.0.0, and nothing else . N...