The attached-bit advertise command configures a rule for setting the ATT bit in Link state Protocol Data Units (LSPs).
The undo attached-bit advertise command restores the default setting rule.
By default, the Level-1-2 device sets the ATT bit in LSPs using the default rule.
| Parameter | Description | Value |
|---|---|---|
| always | Indicates that the ATT bit is set to 1. | - |
| never | Indicates that the ATT bit is set to 0. | - |
Usage Scenario
An ATT bit is a field in link state packets. An ATT bit identifies whether Level-1 area is attached to other areas. A Level-1-2 device sets the ATT bit to 1 to notify the devices in Level-1 area of its attachment to a Level-2 backbone area. After a Level-1 device receives the LSPs carrying the ATT bit 1 from the Level-1-2 device, the Level-1 device generates a route with the same destination address as the default route of the Level-1-2 device. Traffic can be forwarded along this route.
If you want the ATT bit in LSPs to be set to 1, run the attached-bit advertise always command.
Run the attached-bit advertise never command on the Level-1-2 device to disable the device from sending LSPs with the ATT bit 1.
Run the attached-bit avoid-learning command on the Level-1 device that is connected to the Level-1-2 device.
Running the attached-bit advertise never command applies to all Level-1 devices that receive LSPs with the ATT bit 0. Therefore, it is more convenient.
Precautions
The ATT bit is defined in both Level-1 and Level-2 LSPs, but it can be set to 1 only in Level-1 LSPs. Additionally, only the Level-1-2 device can set the ATT bit. Therefore, running the attached-bit avoid-learning command takes effect only on the Level-1-2 device.