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mediumbgp~60 min

BGP won't come up between two ASes

An eBGP session between two providers won't establish, and even once it does, a prefix is missing. Fix both.

Scenario

Two organizations are peering over eBGP across a direct link. The link is up and the routers can ping each other, but the BGP session is stuck and isn't exchanging routes. After you get the session up, you'll notice one side still isn't advertising its LAN.

Topology

  • R1: AS 65001, LAN 10.0.1.0/24, link IP 10.0.12.1/30
  • R2: AS 65002, LAN 10.0.2.0/24, link IP 10.0.12.2/30
  • host-A 10.0.1.10 behind R1, host-B 10.0.2.10 behind R2

Your job

Get the eBGP session to Established, make sure both LAN prefixes are advertised and learned, and confirm host-A can reach host-B.

What "done" looks like

Session Established, each router has the other's LAN via BGP, and end-to-end ping works.

Teaches: eBGP neighbor parameters must match, and a working session still advertises nothing unless you tell it to.

What gets checked

Your solution is verified against each of these:

  • eBGP session between R1 and R2 reaches Established state
  • R1 has 10.0.2.0/24 in its table, learned via BGP
  • R2 has 10.0.1.0/24 in its table, learned via BGP
  • Ping from host-A (10.0.1.10) to host-B (10.0.2.10) succeeds

Solve it in the browser lab

No setup, no install. Open a live lab: configure each device in the editor or its Cisco IOS terminal, run show/ping/traceroute (or test from the hosts), and watch the network react. The in-house engine grades your fix instantly and issues your proof the moment every check passes.

Open the lab →

Prefer your own lab?

  1. Build the fix locally. New to the tooling? See setting up your lab.
  2. Push your topology file, device configs, and any playbooks to a public repo (GitHub or GitLab).
  3. Submit the repo link. We review it by hand, confirm it works, and issue your proof page.
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