Question 1
In an IS-IS network, what is the role of a Designated Intermediate System (DIS)?
graph TD
subgraph Broadcast Network
R1(Router 1) --- R2(Router 2)
R1 --- R3(Router 3)
R1 --- R4(Router 4)
R2 --- R3
R2 --- R4
R3 --- R4
end
DIS[DIS Creates Pseudonode] --> R1
DIS --> R2
DIS --> R3
DIS --> R4
Answer and explanation
Correct answer: B
On a broadcast network, IS-IS elects a Designated Intermediate System (DIS) to reduce the number of adjacencies and the amount of LSP flooding. The DIS's primary role is to create a 'pseudonode' LSP that represents the broadcast segment itself and lists all the routers attached to it. This simplifies the link-state database, as each router only needs to see the pseudonode instead of forming adjacencies with every other router on the segment.
