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DES-7200 Configuration Guide Chapter 3 BFD Configuration
3-6
1. Active Mode: Before a session is established, BFD actively sends the BFD
control packets regardless of whether any BFD control packet is received
from the peer.
2. Passive Mode: Before a session is established, no BFD control packet is
sent until a BFD control packet is received from the peer.
Cautio
n
In firmware v10.4(1), v10.3(4b3) and v10.3(5), the passive mode
is not supported and can not be configured.
3.2.2 BFD Detection Mode
The BFD detection modes are as follows:
z Asynchronous Mode
In the asynchronous mode, the BFD control packets are sent periodically
among the systems. If one system receives no BFD control packet from the
peer within the BFD interval, the BFD session will be down.
z Demand Mode
In the demand mode, suppose that every system has an independent
method to confirm whether it has been connected to other systems, once a BFD
session is established, the system stops sending the BFD control packets
unless a system needs the connection verification. If the connection verification
is necessary, the system will send a BFD control packet with the short sequence.
If no returned packet is received within the detection interval, the BFD session
will be down. If the echo packet is received from the peer, the forwarding path is
normal.
z Echo Mode
The local system sends the BFD echo packet periodically. The peer system
loops back the echo packet via the forwarding channel. The BFD session will be
down if the continuous echo packets are not received within the detection
interval. The echo mode can be co-used with the above-mentioned two
detection modes. In the echo mode, the packets are forwarded back via the
forwarding panel of the peer system rather than the control panel, reducing the
delay and speeding up the fault detection in comparison to the control packet
sending. In the asynchronous mode, the control packet sending will be
decreased with the echo function enabled, for the echo function processes the
detection. If the echo function is enabled in the demand mode, the control
packet sending can be cancelled after the BFD session establishment. The
echo function must be enabled in the BFD session, otherwise the echo function
will be invalid.