Forums bury the answer under 40 replies. Vendor docs assume you already know the feature name. This library starts where an outage starts — the exact symptom on your screen — then gives you checks in order, ranked causes, a safe fix, and proof it worked. Every page is written in plain English.
Two routers that should exchange routes sit forever in the state EXSTART (or bounce between EXSTART and DOWN).
Engineers search this as: 'ospf neighbor stuck in exstart' · 'ospf exstart exchange mtu'
A BGP session never comes up.
Engineers search this as: 'bgp neighbor stuck in active' · 'bgp active state no connection'
A switch port shuts itself off.
Engineers search this as: 'port err-disabled link flap' · 'how to fix errdisable'
The Error Decoder translates the cryptic lines your switches and routers print — what the message means, what usually causes it, the commands to check, and the fix. Popular right now:
%PM-4-ERR_DISABLE %PORT_SECURITY-2-PSECURE_VIOLATION %BGP-5-ADJCHANGE %OSPF-5-ADJCHG %LINK-3-UPDOWN %CDP-4-DUPLEX_MISMATCH
No 40-reply threads, no "it worked for me" guesses, no answers for a software version from 2012. Every case ends in a verdict: the fix, and the output that proves it.
Docs are organized by feature. Outages are organized by symptom. These pages start from what is on your screen, and cross vendors where the problem does.
Every answer is written from vendor documentation and RFCs, with the source named on the page. And Packet Path's labs can reproduce many of these faults, so you can practice the fix safely first.
When the fire is out: 31 free network tools for the calculating and checking, and 228 hands-on labs to practice the next fault before it happens.