Controlling Whether a Level-1 Device Generates a IPv4 Default Route

Context

As defined in the IS-IS protocol, if a Level-1-2 device reaches more areas through a Level-2 area than through a Level-1 area based on the link state database (LSDB), the Level-1-2 device sets the ATT bit to 1 in the LSPs and sends the LSPs with the ATT bit 1 to the Level-1 device. Upon receipt, the Level-1 device generates a default route destined for the Level-1-2 device.

The preceding rules are used by default. You can set the ATT bit as required on a live network.

Perform the following steps:

Procedure

Run system-view
The system view is displayed.
Run isis [ process-id ]
The IS-IS view is displayed.
Run the following command as required:
- To set the ATT bit in the LSPs sent by the Level-1-2 device, run the attached-bit advertise { always | never } command.
  - If the always parameter is specified, the ATT bit is set to 1. After receiving the LSPs carrying the ATT bit 1, the Level-1 device generates a default route.
  - If the never parameter is specified, the ATT bit is set to 0. After receiving the LSPs carrying the ATT bit 0, the Level-1 device does not generate a default route, which reduces the size of a routing table.
- To disable the Level-1 device from generating default routes even though it receives the LSPs carrying the ATT bit 1, run the attached-bit avoid-learning command.