Example for Configuring IS-IS Fast Convergence

Procedure

1. Configure IP addresses for interfaces on each router.

   # Configure RouterA.

   <Huawei> system-view

   [Huawei] sysname RouterA

   [RouterA] interface gigabitethernet 1/0/0

   [RouterA-GigabitEthernet1/0/0] ip address 10.1.1.1 24

   [RouterA-GigabitEthernet1/0/0] quit

   The configuration of RouterB is similar to the configuration of RouterA, and is not mentioned here.

2. Configure basic IS-IS functions.

   # Configure RouterA.

   [RouterA] isis 1

   [RouterA-isis-1] is-level level-2

   [RouterA-isis-1] network-entity 10.0000.0000.0001.00

   [RouterA-isis-1] quit

   [RouterA] interface gigabitethernet 1/0/0

   [RouterA-GigabitEthernet1/0/0] isis enable 1

   [RouterA-GigabitEthernet1/0/0] quit

   # Configure RouterB.

   [RouterB] isis 1

   [RouterB-isis-1] is-level level-2

   [RouterB-isis-1] network-entity 10.0000.0000.0002.00

   [RouterB-isis-1] quit

   [RouterB] interface gigabitethernet 1/0/0

   [RouterB-GigabitEthernet1/0/0] isis enable 1

   [RouterB-GigabitEthernet1/0/0] quit

3. Configure BFD.

   # Configure RouterA.

   [RouterA] bfd

   [RouterA-bfd] quit

   [RouterA] bfd atob bind peer-ip 10.1.1.2 interface gigabitethernet 1/0/0

   [RouterA-bfd-session-atob] discriminator local 1

   [RouterA-bfd-session-atob] discriminator remote 2

   [RouterA-bfd-session-atob] commit

   [RouterA-bfd-session-atob] quit

   [RouterA] interface gigabitethernet 1/0/0

   [RouterA-GigabitEthernet1/0/0] isis bfd static

   [RouterA-GigabitEthernet1/0/0] quit

   # Configure RouterB.

   [RouterB] bfd

   [RouterB-bfd] quit

   [RouterB] bfd btoa bind peer-ip 10.1.1.1 interface gigabitethernet 1/0/0

   [RouterB-bfd-session-btoa] discriminator local 2

   [RouterB-bfd-session-btoa] discriminator remote 1

   [RouterB-bfd-session-btoa] commit

   [RouterB-bfd-session-btoa] quit

   [RouterB] interface gigabitethernet 1/0/0

   [RouterB-GigabitEthernet1/0/0] isis bfd static

   [RouterB-GigabitEthernet1/0/0] quit

4. Set the time parameters of fast convergence.

   # Configure RouterA.

   [RouterA] isis 1

   [RouterA-isis-1] flash-flood

   [RouterA-isis-1] timer spf 1 20 100

   [RouterA-isis-1] timer lsp-generation 1 1 120

   [RouterA-isis-1] quit

   # Configure RouterB.

   [RouterB] isis 1

   [RouterB-isis-1] flash-flood

   [RouterB-isis-1] timer spf 1 20 100

   [RouterB-isis-1] timer lsp-generation 1 1 120

   [RouterB-isis-1] quit

   • In IS-IS, if the LSDB changes, routes are calculated and a new LSP is generated to report this change. Frequent route calculations consume a lot of system resources and decrease the system performance. Delaying SPF calculation and LSP generation and speeding up LSP flooding can improve the efficiency in route calculation and reduce the consumption of system resources.

   • The flash-flood command enables LSP fast flooding to speed up IS-IS network convergence.

   • The timer spf command sets the interval for SPF calculation. The default interval is 5 seconds.

   • The timer lsp-generation command sets the delay in generating an LSP. The default interval is 2 seconds.

5. Verify the configuration.

   # Run the shutdown command on GE1/0/0 of RouterB to shut down the link.

   [RouterB] interface gigabitethernet 1/0/0

   [RouterB-GigabitEthernet1/0/0] shutdown

   # View the information about neighbors of RouterA.

   <RouterA> display isis peer

   INformation about neighbors of RouterA does not exist.

   When BFD detects that the link goes Down, it notifies the routing management (RM) module immediately. IS-IS then deletes the neighbor relationship immediately and triggers route calculation. This implements fast convergence of the network.