BGP/RPKI track · Lab 02 overview

Route appearance, withdrawal, and return.

Lab 02 keeps the two-router setup from Lab 01 and adds movement: one route appears on r2, is withdrawn by r1, then is announced again.

Verified on Linux 2026-05-08 Estimated time: 45-60 min Focus: RFC 4271 UPDATE

これは初級の containerlab コースです

従来の hands-on コースとして、route の出現、withdrawal、再広告を手元で観測します。 初級コースの 2 本目として、BGP UPDATE message の意味を実験ベースでつかむページです。

位置づけ: Beginner Lab 02 / 3
先に読む RFC: RFC 4271 Sections 3.1, 4.3, 5, 5.1.1-5.1.3
前の lab: One Prefix Announcement You Can Explain
次の lab: Competing Origins and the First Route-Leak Question
難易度: hands-on 中級入口
想定時間: 45-60 分
前の lab 次の lab

What this lab is for

This lab shows that a BGP UPDATE message can announce reachability and can also withdraw reachability. The route is intentionally small and local: 203.0.113.0/24 moves through visible states on r2.

route sequence 
203.0.113.0/24 is visible on r2
203.0.113.0/24 is withdrawn by r1
203.0.113.0/24 disappears from r2
203.0.113.0/24 is announced again by r1
203.0.113.0/24 returns on r2

The useful distinction is between withdrawing a route and breaking a BGP session. In this lab the neighbor relationship remains the context; the route itself is what changes.

The experiment

AS65001 on r1 first advertises 203.0.113.0/24 to AS65002 on r2. Then r1 removes the network statement, causing a withdrawal. Finally, r1 adds the network statement back and sends a fresh announcement.

ObservationProtocol meaning
203.0.113.0/24 appearsAnnouncement UPDATE carries the prefix as NLRI with path attributes.
10.0.0.1NEXT_HOP for the advertised route.
65001 iAS_PATH 65001 and ORIGIN IGP.
route disappearsWithdrawal UPDATE carries the prefix in Withdrawn Routes.
route returnsA new announcement installs the route again on r2.

RFC reading path

Lab 02 reads a narrow path through RFC 4271. The focus is UPDATE message structure and the difference between NLRI and Withdrawn Routes.

  • Section 3.1 for route advertisement and withdrawal.
  • Section 4.3 for UPDATE message fields: Withdrawn Routes, Path Attributes, and NLRI.
  • Section 5 for mandatory attributes on announcements.
  • Sections 5.1.1, 5.1.2, and 5.1.3 for ORIGIN, AS_PATH, and NEXT_HOP.

Verified result

The verified run from 2026-05-08 records the route present on r2, absent after withdrawal, and present again after re-advertise.

verified excerpt 
before withdraw:
*> 203.0.113.0/24   10.0.0.1                 0             0 65001 i

after withdraw:
No BGP prefixes displayed, 0 exist

after reannounce:
*> 203.0.113.0/24   10.0.0.1                 0             0 65001 i
Safety note: 203.0.113.0/24 is a documentation prefix. The lab keeps it inside a local environment and does not advertise anything to the public Internet.
Open the full Lab 02 walkthrough

Next labs

After seeing a route move through announcement and withdrawal, the track can add competing origins, route leaks, and RPKI origin validation.

Lesson navigation

前に戻るなら Lab 01、続けるなら Lab 03 で competing origins を観察します。

Open Lab 03 overview Back to Lab 01