Hello @M.Sultan,
Difficult to summurarize BGP with significant fundamentals. To much things to say!
BGP is a path vector protocol, which means it advertises the path (sequence of ASNs) that a packet should take to reach a destination network. This path information is used to make routing decisions. BGP has multiple versions, including BGP-4, which is widely used in today's networks.
An AS is a collection of IP networks and routers under the control of a single organization and sharing a common routing policy. BGP operates at the AS level, making it suitable for inter-domain routing (routing between different organizations).
BGP routers establish peering sessions with neighboring BGP routers (tcp_179). BGP sessions can be either eBGP (between routers in different ASes) or iBGP (between routers within the same AS). BGP uses a set of attributes associated with routes to make routing decisions. Find few attributes bellow:
-AS Path: A list of ASNs through which the route has passed. Helps prevent routing loops.
-Next Hop: The IP address of the next-hop router for the route,
-Prefix Length: The length of the network prefix in CIDR notation,
-Local Preference: Used in route selection within an AS,
-Weight: Cisco-specific attribute used for route selection within a router,
-MED: Used for route selection between ASes,
-Community: A tag used for policy manipulation.
BGP uses a combination of these attributes to select the best path to reach a destination. The BGP decision process evaluates attributes to determine the best route.
Net admin can apply route filters and policies to manipulate BGP routes based on specific criteria.
Best regards
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