BFD is a simple “Hello” protocol，similar with routing protocol’s neighbor detection.By fast sending timely 
detection packets on established communication channels, provide the detection function.Currently the most 
used of fast fault detection is BFD(Bidirectional Forwarding Detection).


BFD protocol provide bidirectional detection mechanism, can be divided into two types.
Asynchronous mode and inquiry mode, one assistant function is echo function, it can
work together with the two modes. For Asynchronous mode and inquiry mode, the key
point of difference is that the location of detection. For asynchronous mode, local side timely
sending BFD control packet, on the remote side detect the BFD control packets, while for
inquiry mode, the sending and detection are both on local side.

In asynchronous mode timely sending BFD control packet, if not received any BFD 

packet sent from peer side in the detection time, means the session down.

In inquiry mode, suppose that each end have a special method to check the
connection to the peer, when BFD session is established, it will stop sending the
BFD control packet. Only when the system need to identify the connection
explicitly, then it will send out some BFD control packets, in the detection time, if
no receive any reply packet, means session down, others ,system keep silent again
and not send the BFD control packet.


In echo function, Local side send out some BFD echo packets, for the peer side, it would loop them
back, in the detection time, if no receive any back packet, means session down.
Echo function can be provided together with the two detection modes.

Thank you for the knowledge

Thank you for sharing.

If you can give us some network examples will be praised.

bfd to-bg_bog3_ar2 bind peer-ip 10.252.20.1

bfd to-cg_ptl3_ar2 bind peer-ip 10.252.12.1

bfd to-mgw60-1 bind peer-ip 10.187.4.14 interface GigabitEthernet1/0/9
bfd to-mgw60-2 bind peer-ip 10.187.4.18 interface GigabitEthernet2/0/2

<SV_SAV4_NE40E_AR2>display bfd session all 
--------------------------------------------------------------------------------
Local Remote PeerIpAddr      State     Type        InterfaceName                
--------------------------------------------------------------------------------

8250  215    10.248.3.10     Up        D_IP_IF     Eth-Trunk1                   
8007  8006   10.187.4.14     Up        S_IP_IF     GigabitEthernet1/0/9         
8009  8008   10.187.4.18     Up        S_IP_IF     GigabitEthernet2/0/2         

2     1      10.248.3.1      Up        S_IP_IF     Vlanif2 

It will be very helpful if you give us some suggestions on product document.

nice sharing

good job

helpful documentation with examples

thanks for share

thanks for share