R3102-R3103-HP 6600/HSR6600 Routers High Availability Configuration Guide

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BFD packet format
BFD control packets are encapsulated into UDP packets with port number 3784 for single-hop
detection or port number 4784 for multi-hop detection (also can be 3784 based on the configuration
task). BFD 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 58
illustrates the packet format.
Figure 58 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
Diag
Description
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
Vers Diag
Sta
P F C A D Detect Mult Length
My Discriminator
Your Discriminator
Desired Min TX Interval
Required Min RX Interval
Required Min Echo RX Interval
Auth Type Auth Len Authentication Data...
0 7
R
23 31