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BeginnerPublished 2026-07-03

eBGP Fundamentals: The First Peering

Free preview — the first lab of BGP Fundamentals

Build your first external BGP (eBGP) peering between two routers in different autonomous systems over a /30 point-to-point link and exchange one /24 prefix from each side using Loopback0. The topology is intentionally small yet realistic, with two edge routers (AS 65001 and AS 65002) and three Alpine hosts for basic reachability checks and operator context. You will configure deterministic BGP neighbors, originate prefixes with exact-match network statements, and validate reachability and route installation using standard IOS and Linux tools. This is Lab 1 of 10 in the CCNP-aligned BGP Fundamentals series and sets the foundation for later labs on iBGP, route filtering, and path selection.

Track
Est. time
35 minutes
Difficulty
Beginner
Topics

Learning objectives

  • Configure an eBGP neighbor over a directly connected /30 using neighbor remote-as with different ASNs.
  • Set a stable BGP router-id and originate a /24 from Loopback0 using the exact-match network mask.
  • Verify session formation and route installation with show ip bgp summary, show ip bgp, and show ip route bgp.
  • Confirm end-to-end reachability to the remote advertised Loopback using ping sourced from the local Loopback.
  • Recognize common eBGP bring-up pitfalls: wrong remote-as, missing exact-match network, or addressing mismatch.

Troubleshooting focus

  • If the neighbor stays in Idle or Active, confirm the directly connected transit IPs and that the neighbor remote-as values are swapped correctly.
  • If prefixes do not appear in BGP, ensure the network statement includes the mask keyword and that an exact route exists in the RIB.
  • Check for typos in IP addresses on the transit interface; both ends must be in the same /30.
  • Use show ip bgp neighbors to confirm BGP capabilities and that no inbound/outbound filters are suppressing routes.
  • Ping the neighbor’s transit IP before expecting BGP to establish (eBGP default TTL is 1 over a direct link).

Topology

Lab topology diagram

Related labs

More hands-on Cisco Modeling Labs practice on the same track and topics.

Grade your work

How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
  • Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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