The scenario
ISP-A (AS 65001) serves Host-A on 172.16.1.0/24. ISP-B (AS 65002) serves Host-B, a web server on 172.16.2.0/24. The two routers share one link, 10.0.0.0/29, and run an eBGP session across it. Neither router has a static route and neither runs OSPF, so the only way ISP-A can know about 172.16.2.0/24 is for ISP-B to tell it over BGP, and the other way round. You will see the learned routes, add a new customer network on ISP-B and watch ISP-A learn it without touching ISP-A, then break the session with a wrong address and watch every route it carried vanish.
What you will work out
Understand what a BGP session needs, what the routers advertise over it, and how to tell a BGP-learned route from a configured one.
Why this matters
BGP is how separate networks on the internet tell each other which addresses they can reach. Cloud providers and content networks announce their address ranges with it, and a session that will not come up, or a route that is not advertised, is a common reason one network cannot reach another. The first checks are the ones in this lab: is the session Established, and is the route in the table as a BGP route?
Running it
BGP: Two ISPs Exchanging Routes opens on a canvas, already wired and addressed. Trace a packet through it hop by hop, or run the same topology live on real Linux network namespaces. How the two modes differ.
Open BGP: Two ISPs Exchanging Routes
Runs in your browser. No install, no signup, and the simulation starts instantly.
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