Configuring BFD-IS-IS Interworking

You can configure BFD interworking with IS-IS in the scenarios with high requirements on data transmission and IS-IS convergence needs to be sped up upon link status changes.

Prerequisites

Before you configure BFD-IS-IS interworking, complete the following tasks on devices at both ends:

Setting the IP addresses of interfaces to ensure reachable adjacent nodes.
Configuring basic IS-IS functions to enable neighbor relationship in Full state. For details, see Configuring IS-IS.
Configure global BFD functions, including enabling BFD and adjusting global parameters. For details, see Configuring Global BFD Functions.
To configure static BFD interworking with IS-IS, manually configure static BFD sessions first. For details, see Creating a Static BFD Session.

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.

BFD interworking with IS-IS can be static or dynamic.

A static BFD session can only be established and released manually. A configuration error will lead to a BFD failure. For example, if a local or remote discriminator is incorrectly configured, a BFD session will not work properly.

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 static BFD on an interface.
1. Access the system view.
  system-view
2. Access the interface view.
  interface interface-type interface-number
3. Enable static BFD.
  isis bfd static
Enable dynamic BFD for an IS-IS IPv4 process.
1. Access the system view.
  system-view
2. Access the IS-IS view.
  isis [ process-id ]
3. 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.
4. (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.
5. Return to 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. Access the interface view.
  interface interface-type interface-number
3. 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.
4. (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.