RFC 5880 · June 2010 · D. Katz, D. Ward
Bidirectional Forwarding Detection (BFD)
Index fetched 2026-10-19 from rfc-editor.org
How it works
Built by hand from RFC 5880. Every arrow, step and field cites the RFC sentence it comes from, and an automated test checks each quote against the RFC text. Provisional: not yet reviewed by a second engineer. Help verify this visual
| From → To | Event / action | Source |
|---|---|---|
| Down → Init | rcv State Down | RFC 5880 §6.8.6 If bfd.SessionState is Down If received State is Down Set bfd.SessionState to Init |
| Down → Up | rcv State Init | RFC 5880 §6.8.6 Else if received State is Init Set bfd.SessionState to Up |
| Init → Up | rcv State Init or Up | RFC 5880 §6.8.6 Else if bfd.SessionState is Init If received State is Init or Up Set bfd.SessionState to Up |
| Down → AdminDown | admin disable / stop EchoThe procedure applies to a session in any state; only the move from Down is drawn. | RFC 5880 §6.8.16 Else Set bfd.SessionState to AdminDown Set bfd.LocalDiag to an appropriate value Cease the transmission of BFD Echo packets |
| AdminDown → Down | admin enable | RFC 5880 §6.8.16 If enabling session Set bfd.SessionState to Down Else Set bfd.SessionState to AdminDown |
What each state means
- Down
- RFC 5880 §6.2
Down state means that the session is down (or has just been created).
- Init
- RFC 5880 §6.2
Init state means that the remote system is communicating, and the local system desires to bring the session up, but the remote system does not yet realize it.
- Up
- RFC 5880 §6.2
Up state means that the BFD session has successfully been established, and implies that connectivity between the systems is working.
- AdminDown
- RFC 5880 §6.2
AdminDown state means that the session is being held administratively down.
Not shown: Administrative disable (to AdminDown) from Init and Up, and Init to Down on a received AdminDown: the RFC's rules cover them but do not name those states; The optional Authentication Section (Auth Type, Auth Len, Authentication Data) and its formats (sections 4.2-4.4, 6.7); Packet validity checks that discard a received Control packet before the state machine runs (section 6.8.6); Demand mode, the Poll Sequence and Echo function (sections 6.4-6.6, 6.8.5); Timer negotiation and Detection Time calculation details (sections 6.8.2-6.8.4); BFD Echo packet format (section 5); A message sequence: the RFC describes the three-way handshake in prose only, with no exchange figure.
Lineage
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