Configuring the Cost of an IS-IS Interface

Context

The costs of IS-IS interfaces can be determined in the following modes in descending order of priority:

Interface cost: is configured for a specified interface.
Global cost: is configured for all interfaces.
Automatically calculated cost: is automatically calculated based on the interface bandwidth.

If no cost is configured for an IS-IS interface, the IS-IS interface uses the default cost 10 and cost style narrow.

If you want to change the cost style of IS-IS devices, running the command while configuring basic IS-IS functions is recommended. If the cost style of IS-IS devices is changed during network operation, the IS-IS process is restarted and the neighbor relationship is re-established.

Procedure

Configure the IS-IS cost style.
1. Run system-view
  
  The system view is displayed.
2. Run isis [ process-id ]
  
  The IS-IS view is displayed.
3. Run cost-style { narrow | wide | wide-compatible | { narrow-compatible | compatible } [ relax-spf-limit ] }
  
  The IS-IS cost style is configured.
  
  By default, the cost style of routes received and sent by an IS-IS device is narrow.
The cost range of an interface and a route received by the interface vary with the cost type.
- If the cost style is narrow, the cost of an interface ranges from 1 to 63. The maximum cost of a route received by the interface is 1023.
- If the cost style is narrow-compatible or compatible, the cost of an interface ranges from 1 to 63. The cost of a received route is related to relax-spf-limit.
- If the cost style is wide-compatible or wide, the cost of the interface ranges from 1 to 16777215. When the cost is 16777215, the neighbor TLV generated on the link cannot be used for route calculation but for the transmission of TE information. The maximum cost of a received route is 0xFFFFFFFF.

Configure the cost of an IS-IS interface.

Perform any of the following operations to configure the cost of an IS-IS interface.

Configure the cost of a specified IS-IS interface.

Run system-view

The system view is displayed.
Run interface interface-type interface-number

The interface view is displayed.
(Optional) On an Ethernet interface, run undo portswitch
The interface is switched to Layer 3 mode.

By default, an Ethernet interface works in Layer 2 mode.

Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
Run isis cost { cost | maximum } [ level-1 | level-2 ]

The cost of the IS-IS interface is configured.

By default, the link cost of an IS-IS interface is 10.

You can configure the parameter maximum only when the IS-IS cost style is wide or wide-compatible.

To change the cost of a loopback interface, run the isis cost command only in the loopback interface view.

Configure the global IS-IS cost.

Run system-view

The system view is displayed.
Run isis [ process-id ]

The IS-IS view is displayed.
Run circuit-cost { cost | maximum } [ level-1 | level-2 ]

The global IS-IS cost is configured.

By default, no global cost is configured.

Enable IS-IS to automatically calculate the interface cost.

Run system-view

The system view is displayed.
Run isis [ process-id ]

The IS-IS view is displayed.
Run bandwidth-reference value

The reference value of the bandwidth is configured. By default, the bandwidth reference value is 100 Mbit/s.
Run auto-cost enable [ compatible ]

The interface is configured to automatically calculate its cost.

The bandwidth reference value set using the bandwidth-reference command takes effect only when the cost style is wide or wide-compatible. In this case, the interface cost is calculated using the following formula:

Cost of each interface = (Bandwidth-reference/Interface bandwidth) × 10

If the cost-style is narrow, narrow-compatible, or compatible, the cost of each interface is calculated based on costs listed in Table 1.

**Table 1** Mapping between IS-IS interface costs and interface bandwidth
Cost	Bandwidth Range
60	Interface bandwidth ≤ 10 Mbit/s
50	10 Mbit/s < Interface bandwidth ≤ 100 Mbit/s
40	100 Mbit/s < Interface bandwidth ≤ 155 Mbit/s
30	155 Mbit/s < Interface bandwidth ≤ 622 Mbit/s
20	622 Mbit/s < Interface bandwidth ≤ 2.5 Gbit/s
10	2.5 Gbit/s < Interface bandwidth