Understanding IS-IS Designated Routers

A router advertises its priority to become a designated router in its hello packets. On all multiaccess 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. The router with the highest priority is elected as the designated router. 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.

Related Topics

• Junos OS Feature Support Reference for SRX Series and J Series Devices
• IS-IS Overview
• Configuring IS-IS Designated Routers (CLI Procedure)