BFD (`bfd`)

Layer: Application and control
Header: variable length
Notes: LDP / RSVP-TE / BFD (P2)

Reached from

Lower layer	Selector	Value
`udp`	`dst_port` / `src_port`	3784 (0x0ec8)
`udp`	`dst_port` / `src_port`	4784 (0x12b0)
`udp`	`dst_port` / `src_port`	6784 (0x1a80)

Fields

Field	Type	Default	Auto	Description
`version`	`uint(3)`	`1`		BFD version (1).
`diag`	`enum(5)`	`0` (no_diagnostic)		Diagnostic code: the reason of the last state change of the local session.
`state`	`enum(2)`	`1` (down)		Session state: 0 AdminDown, 1 Down, 2 Init, 3 Up.
`p`	`uint(1)`	`0`		P bit: Poll (a parameter change, the peer answers with F).
`f`	`uint(1)`	`0`		F bit: Final (answer to a Poll).
`c`	`uint(1)`	`0`		C bit: Control Plane Independent.
`a`	`uint(1)`		Number of items of `authentication`	A bit: authentication present (Auto: set when there is an authentication section).
`d`	`uint(1)`	`0`		D bit: Demand mode.
`m`	`uint(1)`	`0`		M bit: Multipoint (0).
`detect_mult`	`uint(8)`	`3`		Detect time multiplier.
`length`	`uint(8)`		Length of the header in octets	Length of the control packet in octets, including the authentication section (Auto).
`my_discriminator`	`uint(32)`	`1`		My discriminator: a non-zero value unique to the session on the sender.
`your_discriminator`	`uint(32)`	`0`		Your discriminator: the peer’s discriminator (0 while unknown).
`desired_min_tx_interval`	`uint(32)`	`1000000`		Desired minimum TX interval in microseconds.
`required_min_rx_interval`	`uint(32)`	`1000000`		Required minimum RX interval in microseconds.
`required_min_echo_rx_interval`	`uint(32)`	`0`		Required minimum echo RX interval in microseconds (0 = no echo).
`authentication`	`tlv` — `length - 24` octets			Authentication section (8-bit type, 8-bit length including the header): simple password, keyed MD5 / SHA1 and their meticulous variants. The digest / hash is Manual.

`diag`

Value	Name
0	`no_diagnostic`
1	`control_detection_time_expired`
2	`echo_function_failed`
3	`neighbor_signaled_session_down`
4	`forwarding_plane_reset`
5	`path_down`
6	`concatenated_path_down`
7	`administratively_down`
8	`reverse_concatenated_path_down`
9	`mis_connectivity_defect`

`state`

Value	Name
0	`admin_down`
1	`down`
2	`init`
3	`up`

`authentication`

Type 8 bits, length 8 bits.
The length counts the type and length fields too.
Unknown types are kept as raw value octets.

Type	Name	Value fields	Description
1 (0x01)	`simple_password`	`key_id`, `password`
2 (0x02)	`keyed_md5`	`key_id`, `reserved`, `sequence_number`, `digest`
3 (0x03)	`meticulous_keyed_md5`	`key_id`, `reserved`, `sequence_number`, `digest`
4 (0x04)	`keyed_sha1`	`key_id`, `reserved`, `sequence_number`, `hash`
5 (0x05)	`meticulous_keyed_sha1`	`key_id`, `reserved`, `sequence_number`, `hash`

`authentication` › `simple_password`

Field	Type	Default	Auto	Description
`key_id`	`uint(8)`	`1`
`password`	`bytes` — rest of the PDU

`authentication` › `keyed_md5`

Field	Type	Default	Auto	Description
`key_id`	`uint(8)`	`1`
`reserved`	`uint(8)`	`0`
`sequence_number`	`uint(32)`
`digest`	`bytes(16)`

`authentication` › `meticulous_keyed_md5`

Field	Type	Default	Auto	Description
`key_id`	`uint(8)`	`1`
`reserved`	`uint(8)`	`0`
`sequence_number`	`uint(32)`
`digest`	`bytes(16)`

`authentication` › `keyed_sha1`

Field	Type	Default	Auto	Description
`key_id`	`uint(8)`	`1`
`reserved`	`uint(8)`	`0`
`sequence_number`	`uint(32)`
`hash`	`bytes(20)`

`authentication` › `meticulous_keyed_sha1`

Field	Type	Default	Auto	Description
`key_id`	`uint(8)`	`1`
`reserved`	`uint(8)`	`0`
`sequence_number`	`uint(32)`
`hash`	`bytes(20)`

Constraints

Level	Rule
warning	`version` = 1
warning	`detect_mult` ≠ 0
warning	`my_discriminator` ≠ 0
error	header at least 24 octets

Sample templates

interop-bfd-session-up — templates/interop/bfd-session-up.wpg.yaml
bfd-auth — templates/protocols/oam/bfd-auth.wpg.yaml
bfd-multihop-ipv6 — templates/protocols/oam/bfd-multihop-ipv6.wpg.yaml
bfd-single-hop — templates/protocols/oam/bfd-single-hop.wpg.yaml
micro-bfd — templates/protocols/oam/micro-bfd.wpg.yaml