R3303-HP HSR6800 Routers High Availability Configuration Guide

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echo packets have a similar format as BFD control packets with UDP port number 3785 except that the
Desired Min TX Interval and Required Min RX Interval fields are null. Figure 54 illu
strates the packet
format.
Figure 54 BFD packet format
• Vers—Protocol version. The protocol version is 1.
• Diag—This bit indicates the reason for the last transition of the local session from up to some other
state. Table 19 lists
the states.
Table 19 Diag bit values
Dia
g
Descri
p
tion
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.
9–31 Reserved for future use.
• State (Sta)—Current BFD session state. Its value can be 0 for AdminDown, 1 for Down, 2 for Init,
and 3 for Up.
• Poll (P)—If set, the transmitting system is requesting verification of connectivity, or of a parameter
change. If clear, the transmitting system is not requesting verification.
• Final (F)—If set, the transmitting system is responding to a received BFD control packet that had the
Poll (P) bit set. If clear, the transmitting system is not responding to a Poll.
• Control Plane Independent(C)—If set, the transmitting system's BFD implementation does not share
fate with its control plane. That is, BFD is implemented in the forwarding plane and can continue to
function through disruptions in the control plane. If clear, the transmitting system's BFD
implementation shares fate with its control plane.
• Authentication Present (A)—If set, the Authentication Section is present and the session is to be
authenticated.