When an error or anomaly happens on a BGP network, BGP will generate a “Notification Message.” As a Network Engineer, this is one message that you do not want to see. This message indicates a problem on your network that caused your BGP peering to fail or stops your BGP peers from forming a neighborship. The possible error codes are:
| Error Code | Error Subcode |
| 1 – Message Header Error | 1- Connection Not Synchronized |
| 2- Bad Message Length | |
| 3- Bad Message Type | |
| 2 – Open Message Error | 1- Unsupported Version Number |
| 2- Bad Peer AS | |
| 3- Bad BGP Identifier | |
| 4- Unsupported Optional Parameter | |
| 5- Authentication Failure | |
| 6- Unacceptable Hold-Timer | |
| 7- Unsupported Capability | |
| 3 – Update Message Error | 1- Malformed Attribute List |
| 2- Unrecognized Well-Known Attribute | |
| 3- Missing Well-Known Attribute | |
| 4- Attribute Flags Error | |
| 5- Attribute Length Error | |
| 6- Invalid Origin Type | |
| 7- AS Routing Loop | |
| 8- Invalid NEXT_HOP attribute | |
| 9- Optional Attribute Error | |
| 10- Invalid Network Field | |
| 11- Malformed AS_Path | |
| 4 – Hold Timer Expired | N/A |
| 5 – FSM Error (for errors detected by FSM) | N/A |
| 6 – Cease (for fatal errors besides ones already listed) | N/A |
An example of a BGP notification Error code for Hold Timer Expiration is shown below:
