The BGP Message types are used to create a NEIGHBOUR relationship and exchange parameters such as the autonomous system number and authentication values. A BGP message is made up of two parts: a BGP header and data. The header format is the same in all of the BGP messages. TCP is used to transmit BGP messages (port 179). The length of the message ranges from 19 to 4096 octets. Each BGP message's header is 19 octets long and consists of three fields.

The types of BGP messages are listed below:

• Open : A BGP adjacency is established using the OPEN message. Before a BGP peering is established, both parties negotiate session capabilities. The BGP version number, ASN of the originating router, Hold TIME, BGP Identifier, and other optional characteristics that define the session capabilities are all included in the OPEN message.
• Keepalive : To ensure that the neighbours are still alive, BGP does not rely on the TCP connection status. Every one-third of the Hold Timer agreed upon between the two BGP routers, keepalive messages are exchanged. Generally, the default Hold Time for  devices is 180 seconds, so the default Keepalive interval is 60 seconds. No Keepalive messages are delivered between BGP neighbours if the Hold Time is set to zero.
• Update : The Update message can EITHER advertise or remove previously advertised routes, or it can do both. When advertising prefixes, the Update message includes the Network Layer Reachability Information (NLRI), which includes the prefix and related BGP PAs. Only the prefix is included in NLRIs that have been WITHDRAWN. To save needless BANDWIDTH, a UPDATE message can be used as a Keepalive.
• Notification : When a BGP session error is discovered, such as a hold timer expiring, neighbour capabilities changing, or a BGP session reset is requested, a Notification message is sent. The BGP connection is closed as a result of this.