6 Bgp Message Types

OPEN Message

Type 1: The OPEN message is identified by Type 1 and is defined in RFC 4271, which serves as the foundation for BGP.
Initialization: This message is not sent until after the TCP session is established between BGP peers. It is used to initiate the BGP setup process between peers.
Content: The OPEN message contains important BGP information, including the BGP version, the Autonomous System Number (ASN) of the sender, the negotiated Hold Time, the BGP Router-ID (RID), and optional parameter capabilities negotiated between the peers.

Type 4: The KEEPALIVE message is designated as Type 4 and is also defined in RFC 4271.
Heartbeat: This message acts as a heartbeat between BGP peers to ensure that the connection remains alive and operational.
Interval: The default KEEPALIVE interval is set to 60 seconds, and it is part of the BGP session's Keepalive mechanism. The Hold Time, by default, is 180 seconds (3 times the KEEPALIVE interval), indicating how long the session should remain active.
Customization: BGP routers can be configured to send KEEPALIVE messages at a different interval or with a Hold Time of 0, effectively disabling KEEPALIVES. The initial KEEPALIVE is sent in response to the initial OPEN message.

Type 2: The UPDATE message is identified by Type 2 and is defined in RFC 4271.
Content: The UPDATE message is used to convey Network Layer Reachability Information (NLRI) and path attributes. It is the primary message for BGP to advertise, withdraw, or modify routes.
Route Updates: This message contains information about routing updates, indicating which routes should be added or withdrawn from the BGP table.

Type 5: The ROUTE REFRESH message is designated as Type 5 and is defined in RFC 2918.
Purpose: This message is used to request a BGP peer to refresh the Adj-RIB-Out (Adjacency Routing Information Base Out). It allows a peer to request the re-advertisement of BGP routes that were previously advertised.
Efficiency: The ROUTE REFRESH message helps optimize BGP routing updates by ensuring that peers have the most current routing information.

Type 3: The NOTIFICATION message is identified by Type 3 and is defined in RFC 4271.
Occurrence: NOTIFICATION messages are seen under various circumstances, such as when a BGP session is reset, BGP capabilities change, or the Hold Timer expires.
Information: These messages provide information about issues or changes in the BGP session, such as errors or notifications of changes that affect the routing updates.

Further Reading:

For more comprehensive details and reference, you can explore the BGP Parameters documentation (opens in a new tab).