Controlling DIS Selection in IS-IS Network

B

The highest priority (and then highest MAC address) is the criterion used to select the DIS. This priority is set on the interface in the IS-IS protocol configuration.

IS-IS (Intermediate System to Intermediate System) is a link-state routing protocol used in large enterprise networks and service provider networks. It is designed to be fast and efficient in finding the best path to a destination. In an IS-IS network, a designated intermediate system (DIS) is elected for each multiaccess network segment, such as an Ethernet LAN. The DIS is responsible for flooding link-state information to all other systems on the same network segment.

To control the selection of the designated intermediate system (DIS) on a specific link in an IS-IS network, we can use the following options:

A. Configure the interface as passive: By configuring an interface as passive, it will not participate in the DIS election process. This means that the interface will not send hello packets or participate in any DIS-related activities. This option is useful when you don't want a particular interface to be the DIS or you want to prevent a specific system from becoming the DIS.

B. Configure a priority on the interface: Each system in an IS-IS network has a priority value associated with it. The system with the highest priority becomes the DIS on a particular network segment. By configuring a priority on the interface, you can control which system becomes the DIS on that network segment. If two systems have the same priority, the system with the highest MAC address becomes the DIS.

C. Configure the hello interval on the interface: Hello packets are used by IS-IS to discover and maintain neighbor relationships. By configuring the hello interval on the interface, you can control how often the hello packets are sent. A lower hello interval means that the DIS election process will happen more frequently, which can be useful in some situations.

D. DIS selection is random in the Junos OS: This option is not correct. In the Junos OS, the DIS is selected based on the priority value assigned to each system.

In conclusion, options A, B, and C are valid ways to control the selection of the designated intermediate system (DIS) on a specific link in an IS-IS network.