BFD diagnostic messages and session states

Important: BFD can only be enabled on provisioned VLAN attachments that use Dataplane version 2. You can view the dataplaneVersion for a VLAN attachment by viewing the attachment details in one of the following ways:

• API: Use the interconnectAttachments.get method. You can use this method on VLAN attachments for either Dedicated Interconnect or Partner Interconnect.
• Google Cloud CLI: Use the gcloud compute interconnects attachments describe ATTACHMENT-NAME command where ATTACHMENT-NAME is the name of the VLAN attachment for either Dedicated Interconnect or Partner Interconnect.

In the output of the API or gcloud CLI command, look for the dataplaneVersion field with a value of 2. If the field is absent from the output, the VLAN attachment is using version 1 and cannot be used with BFD. For more information, contact your customer account team.

RFC 5880 defines diagnostic codes that specify the local system's reason for the last change in the Bidirectional Forwarding Detection (BFD) session state. Diagnostic messages can be helpful indicators when troubleshooting. You can see these messages or codes when viewing Cloud Router status.

The following table lists BFD diagnostic messages, their numeric error codes, and suggested follow-up actions.

BFD diagnostic message	Numeric code	Suggested action
NO_DIAGNOSTIC	0	No diagnostic information is available. For more information, see the BFD State Machine section of RFC 5880 and the BFD session state table in the next section.
CONTROL_DETECTION_TIME_EXPIRED	1	Local BFD did not receive a control packet from the remote side within the (num_rx_interval * bfd multiplier) time period. This could happen when the forwarding link is down or BFD on the remote system is not functioning properly. Check connectivity to the remote system, and check the remote system's BFD session transmit counters.
ECHO_FUNCTION_FAILED	2	—
NEIGHBOR_SIGNALED_SESSION_DOWN	3	BFD neighbor signaled DOWN. Check the remote system BFD configuration and operational state.
FORWARDING_PLANE_RESET	4	—
PATH_DOWN	5	—
CONCATENATED_PATH_DOWN	6	—
ADMINISTRATIVELY_DOWN	7	BFD in the local system has been set to DOWN by the administrator due to a BFD software upgrade. Check that the state is back up after the upgrade.
REVERSE_CONCATENATED_PATH_DOWN	8	—

BFD session states

The following table lists BFD session states and their numeric error codes.

BFD session state	Numeric code
ADMIN_DOWN	0
DOWN	1
INIT	2
UP	3

BFD status messages

You can view BFD status messages under the bfdStatus field in command output from the gcloud compute routers get-status command.

For field definitions and descriptions, see the Cloud Router API documentation.

What's next

• To modify BFD settings on a BGP session, see Update or disable BFD.

• For information about BGP session states, see BGP session states.

• To troubleshoot issues with Cloud Router, see Troubleshooting.