Configuring Dynamic BFD for IPv4 IS-IS

Dynamic BFD for IPv4 IS-IS can accelerate IS-IS route convergence.

Context

Connection status between an IS-IS device and its neighbors can be monitored by exchanging Hello packets at intervals. The minimum allowable sending interval is 3s, and a neighbor is declared Down after at least three intervals during which no response Hello packet is received from the neighbor. IS-IS takes more than one second to detect that a neighbor becomes Down, resulting in loss of a large amount of high-speed data.

To solve this problem, BFD must be configured for IS-IS. BFD provides millisecond-level fault detection. After detecting a link or node failure, BFD will notify IS-IS of the failure, accelerating the IS-IS route convergence speed.

Dynamic BFD for IPv4 IS-IS implements dynamic setup of BFD sessions. When a new IS-IS neighbor relationship is set up, BFD is notified of the neighbor parameters and the detection parameters (including source and destination IP addresses). Then a BFD session will be established based on the received neighbor parameters. Dynamic BFD is more flexible than static BFD.

Procedure

Enable dynamic BFD for an IS-IS IPv4 process.
1. Access the system view.
  system-view
2. Enable BFD.
  bfd
3. Access the system view.
  quit
4. Access the IS-IS process view.
  isis [ process-id ]
5. Enable BFD for IS-IS.
  bfd all-interfaces enable
  
  After BFD is enabled globally and the neighbor status becomes Up, IS-IS adopts default BFD parameters to establish BFD sessions on all interfaces.
6. (Optional) Set the parameters for establishing BFD sessions for all interfaces.
  bfd all-interfaces { min-rx-interval receive-interval | min-tx-interval transmit-interval | detect-multiplier multiplier-value } ^*
  
  The command execution result is applicable to BFD session parameters on all IS-IS interfaces.
7. Access the system view.
  quit
  
  To disable the BFD function on an interface, run the isis bfd block command in the interface view to disable the interface from establishing BFD sessions.
Enable dynamic BFD on an IPv4 interface.
1. Access the system view.
  system-view
2. Enable BFD.
  bfd
3. Access the system view.
  quit
4. Access the interface view.
  interface interface-type interface-number
5. Enable BFD.
  isis bfd enable
  
  After BFD is configured globally and the neighbor status is Up (on a broadcast network, DIS is in the Up state), default BFD parameters will be used to establish BFD sessions on the specified interface.
6. (Optional) Configure BFD session parameters.
  isis bfd { min-rx-interval receive-interval | min-tx-interval transmit-interval | detect-multiplier multiplier-value } ^*
  
  The priority of BFD configured on an interface is higher than that of BFD configured for a process. If BFD session parameters are configured for both a process and an interface, the parameters on the interface will be used to establish a dynamic BFD session.