HP VPN Firewall Appliances High Availability Configuration Guide

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Dynamic BFD parameter changes
After a BFD session is established, both ends can negotiate the related BFD parameters, such as the
minimum transmit interval, minimum receive interval, initialization mode, and packet authentication
mode. After that, both ends use the negotiated parameters, without affecting the current session state.
Authentication modes
BFD provides the following authentication methods:
• Simple—Simple authentication.
• MD5—MD5 (Message Digest 5) authentication.
• SHA1—SHA1 (Secure Hash Algorithm 1) authentication.
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 160 illu
strate
s the packet
format.
Figure 160 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 29 lists the states.
Table 29 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.