In Border Gateway Protocol (BGP), preventing routing loops is critical — especially because BGP is the inter-domain routing protocol used to connect Autonomous Systems (ASes) on the internet. 🔄 How BGP Prevents Routing Loops The main mechanism BGP uses is the AS_PATH attribute . 🔍 What is AS_PATH? AS_PATH is a BGP path attribute that lists the sequence of Autonomous Systems (AS numbers) a route has traversed. Each time a route is advertised across an AS boundary, the local AS number is prepended to the AS_PATH. Example: If AS 65001 → AS 65002 → AS 65003 is the route a prefix has taken, the AS_PATH will look like: makefile AS_PATH: 65003 65002 65001 It’s prepended in reverse order — so the last AS is first . 🚫 Loop Prevention Using AS_PATH ✅ Core Mechanism: BGP routers reject any route advertisement that contains their own AS number in the AS_PATH. 🔁 Why It Works: If a route makes its way back to an AS that’s already in the AS_PATH , that AS kno...
