Supported Platforms
Example: Configuring IS-IS Designated Routers
Understanding IS-IS Designated Routers
A router advertises its priority to become a designated router in its hello packets. On all multiaccess networks (physical networks that support the attachment of more than two routers, such as Ethernet networks), IS-IS uses the advertised priorities to elect a designated router for the network. This router is responsible for sending network link-state advertisements, which describe all the routers attached to the network. These advertisements are flooded throughout a single area. The priority value is meaningful only on a multiaccess network. It has no meaning on a point-to-point interface.
A router’s priority for becoming the designated router is indicated by an arbitrary number from 0 through 127, which you configure on the IS-IS interface. The router with the highest priority becomes the designated router for the area (Level 1, Level 2, or both), also configured on the IS-IS interface. If routers in the network have the same priority, then the router with the highest MAC address is elected as the designated router. By default, routers have a priority value of 64.
Example: Configuring Designated Router Election Priority for IS-IS
This example shows how to configure the designated router election priority for IS-IS.
Before you begin:
- Configure network interfaces. See the Junos OS Interfaces Configuration Guide for Security Devices.
- Enable IS-IS on the interfaces. See Example: Configuring IS-IS.
In this example, you configure the priority for logical interface ge-0/0/1.0 to be 100 and the level number to be 1. If this interface has the highest priority value, the router becomes the designated router for the Level 1 area.
To configure a designated router election priority for IS-IS:
