Border Gateway Protocol (BGP) is the routing protocol used to exchange routing and reachability information among autonomous systems (AS) on the internet. To facilitate this exchange and maintain peer relationships, BGP utilizes a set of specific message types.
According to NetworkLessons.com, "To do all of this, BGP uses 4 messages: Open Message, Update Message, Keepalive Message, Notification Message." These four messages are fundamental to BGP's operation.
Understanding the Core BGP Messages
Each BGP message serves a distinct purpose in the lifecycle of a BGP peering session, from establishing the connection to exchanging routing information and handling errors.
Here are the four BGP message types:
- Open Message: Used to establish a BGP session between two BGP peers. It includes parameters like the BGP version, AS number, hold time, BGP identifier, and optional parameters.
- Update Message: Carries routing information. It is used to announce new routes, withdraw previously announced routes, or both. Update messages contain Network Layer Reachability Information (NLRI) and path attributes.
- Keepalive Message: Sent periodically to maintain the BGP session between peers. If a peer does not receive an Update or Keepalive message within the negotiated hold time, the session is terminated.
- Notification Message: Sent when an error is detected, and the BGP session is about to be closed. It indicates the type of error that occurred.
BGP Message Types Summary
| Message Type | Primary Purpose |
|---|---|
| Open | Establish and negotiate BGP peering parameters. |
| Update | Exchange routing information (announce/withdraw routes). |
| Keepalive | Maintain the BGP peering session. |
| Notification | Signal errors and close the BGP peering session. |
These four messages enable BGP routers to discover neighbors, exchange reachability information for networks across the internet, ensure the peering session remains active, and handle abnormal situations.
For more details on BGP messages, you can refer to resources like NetworkLessons.com.
