3com S7906E Instruccion De Instalación

 

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No detection time resolution is defined in the BFD draft. At present, most devices supporting BFD 

provide detection measured in milliseconds.  

 

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Single-hop detection: Detects the IP connectivity between two directly connected systems. Single 

hop means one hop for IP forwarding.  

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Multi-hop detection: Detects any of the paths between two systems. These paths may have 

multiple hops and maybe overlapped.  

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Bidirectional detection: Sends detection packets at two sides of a bidirectional link to detect the 

bidirectional link status, thus to implement a link fault detection rate in milliseconds. (BFD LSP 

detection is a special case, in which BFD control packets are sent in one direction, and the peer 

device reports the link status through other links.)  

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Control packet mode: Both ends of the link exchange BFD control packets to monitor link status.  

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Echo mode: One end of the link sends Echo packets to the other end, which then forwards the 

packets back to the originating end, thereby monitoring link status in both directions. 

Before a BFD session is established, there are two BFD operating modes: active and passive.  

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Active mode: In this mode, BFD actively sends BFD control packets regardless of whether any 

BFD control packet is received from the peer.  

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Passive mode: In this mode, BFD does not send control packets until a BFD control packet is 

received from the peer.  

At least one end must operate in the active mode for a BFD session to be established.  

After a BFD session is established, both ends must operate in one of the following two BFD operating 

modes: asynchronous and command.  

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Asynchronous mode: A device operating in the asynchronous mode periodically sends BFD control 

packets. The peer considers that the BFD session is down if it receives no BFD control packet 

within the BFD interval.  

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Demand mode: In this mode, it is assumed that a system has an independent way of verifying the 

connectivity to the peer system. Once a BFD session is established, such a system may stop 

sending BFD control packets, except when the system feels the need to verify connectivity 

explicitly.