In IS-IS, which two statements are correct about the designated intermediate system (DIS) on a multi-access network segment? (Choose two)

In IS-IS, the Designated Intermediate System (DIS) is elected on a multi-access (broadcast) network. The election is based on the interface priority, with the highest priority value winning the election. The default priority is 64. If two or more routers share the highest priority, the router with the highest MAC address (or system ID) becomes the DIS.

Unlike OSPF's Designated Router (DR), the IS-IS DIS does not act as a central point for adjacencies. On an IS-IS multi-access segment, all routers form a full mesh of adjacencies with every other router on that same segment. The primary role of the DIS is to create and flood a pseudonode Link-State PDU (LSP) that represents the multi-access network itself.

B. A router with a priority of 1 would lose the DIS election to a router with a higher priority, as the highest priority value is preferred.

D. This describes OSPF behavior. In IS-IS, all routers on the multi-access segment form adjacencies with each other, not just with the DIS.

1. Juniper Networks TechLibrary

IS-IS Overview: "On broadcast networks

IS-IS uses a designated intermediate system (DIS) to issue LSPs on behalf of the network. The DIS is elected based on the interface priority (the highest priority becomes the DIS). If there is a tie in priority

the router with the highest MAC address is elected." This source validates that the highest priority wins the election (Answer A).

2. Juniper Networks TechLibrary

IS-IS Adjacencies: "On a broadcast subnetwork

all routers form adjacencies with all other routers on the subnetwork. The designated intermediate system (DIS) multicasts pseudonode LSPs to advertise all the routers that are attached to the broadcast subnetwork." This source confirms that a full mesh of adjacencies is formed (Answer C) and not just with the DIS (refuting Answer D).

3. Juniper Networks Day One Library

This Week: An In-Depth Look at IS-IS

page 11: "The router with the highest priority is elected as the DIS. If there is a tie

the router with the highest SNPA (MAC address) is elected... Unlike OSPF

all routers on the LAN will form adjacencies with all other routers on the LAN." This reference supports both correct answers (A and C).