BGP (Border Gateway Protocol) avoids routing loops by implementing the following mechanisms:
1. Path Attribute: BGP uses path attributes to identify the unique path for each route. These attributes are added to the BGP update messages and help to differentiate between the different paths and avoid loops.
1. AS_PATH: BGP uses the AS_PATH attribute to track the path of an IP packet through different Autonomous Systems. When BGP receives a route that includes its own AS number in the AS\_PATH attribute, it knows that a loop has occurred and discards the route.
1. Route Reflection: BGP uses route reflection to reduce the number of updates and avoid loops in a BGP network. Route reflection allows routers within an AS to reflect BGP routes received from one IBGP (Internal BGP) speaker to another IBGP speaker without the need to send the routes to all routers in the AS.
1. Split Horizon: BGP uses split horizon to prevent the advertisement of a route back to the same neighbor it was learned from. This mechanism ensures that BGP does not advertise a route back to the same router that broadcast it, thus preventing routing loops.
1. TTL (Time to Live): BGP uses the TTL (Time to Live) mechanism to prevent routing loops in a network. When a router receives an update, it decreases the TTL value. If the TTL value reaches zero, the update is discarded as it is considered to have expired.
Overall, BGP employs a combination of different mechanisms to ensure that routing loops are avoided, and routes are propagated efficiently throughout a network.