BGP concepts¶
Short primers on the parts of BGP that labs alone don't teach well — the state machine, the attributes, the best-path algorithm, and the policy tooling that makes BGP a policy protocol rather than a routing one.
Read these before Lab 01, alongside it, or as revision. Output shown is captured from the running lab fabric.
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The finite state machine, the four message types, and the timers. Why BGP is deliberately slow, and what each state failure actually tells you.
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Well-known, discretionary, optional transitive — what the categories mean and why they exist. Then each attribute you'll actually manipulate.
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The eleven-step algorithm, in order, with the reason for each step. The single most-asked BGP interview topic.
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Prefix lists, route maps, communities — and the operational safety controls (max-prefix, GTSM, BFD) that keep a peering from taking you down.
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Route reflectors and confederations: why the full mesh doesn't scale, and the loop-prevention that replaces it.
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Self-test bank across the whole phase.
The one-paragraph summary¶
BGP doesn't find the shortest path — it finds the path you said you wanted. Every route carries a set of attributes; your policy sets and reads them; a fixed algorithm compares them in a fixed order and picks a winner. Understand the attributes and the order they're compared in, and BGP stops being mysterious.