What happens in the OpenSent state of BGP?

In the OpenSent state of BGP (Border Gateway Protocol), the primary function is to facilitate the exchange of OPEN messages between BGP peers. When a BGP router enters the OpenSent state, it has already sent an OPEN message to its peer and is awaiting a response. This state conveys that the router is prepared to establish a connection and is waiting to receive an OPEN message back.

When the router receives an OPEN message from its peer, it will process that message. If the OPEN message is valid and meets the necessary criteria (such as proper ASN, parameters, etc.), BGP will transition to the OpenConfirm state. This indicates that the BGP session is advancing towards establishment, where further parameters can be negotiated, ultimately allowing both routers to confirm their connection and parameters before entering the Established state.

The transition from OpenSent to OpenConfirm upon receiving a valid OPEN message is crucial in the establishment of BGP sessions, and it ensures that both peers are configured correctly to communicate with each other.