🌐 BGP Route Propagation Lab

About this simulation

The Border Gateway Protocol (BGP) is how the internet's independently-run networks, called autonomous systems (AS), agree on paths for traffic. There is no central authority — each AS learns routes from its neighbours, applies its own policy to pick a single best path, and re-announces that choice onward. This scene models a small three-tier internet: Tier-1 core carriers, Tier-2 regional ISPs, and Tier-3 edge networks.

How it works

• Announce — the chosen origin AS originates a prefix. The update fans out hop by hop; every AS that receives it compares candidate routes from its neighbours and keeps only the best one, based on the selected policy.
• Withdraw — the origin pulls the route back. ASes that used it must search their remaining neighbours for a backup path (or lose reachability), which is why withdrawals can take longer to settle than announcements — real BGP calls this "path exploration".
• Export rules follow the classic Gao-Rexford model: routes learned from a customer are re-exported to everyone (they earn revenue), while routes learned from a peer or provider are only re-exported to customers — this prevents an AS from being used as free transit.
• The bright blue tree traces each AS's current best path back toward the origin — the AS-level shortest/preferred spanning tree.

Controls

• Origin AS — which network originates the prefix.
• Route-selection policy — "local-pref" prefers routes learned from customers over peers/providers (how real ISPs route for revenue); "shortest AS-path" ignores commercial relationships and always takes the fewest hops.
• Propagation speed — how fast update messages travel along links.
• Announce / Withdraw — trigger the two core BGP events.
• ↺ Rebuild network — regenerates the AS topology and resets state.

Did you know?

Because BGP has no global view, a withdrawn route can briefly cause routers to try several stale alternate paths before settling — a real phenomenon called BGP path exploration that can take tens of seconds on the real internet.