Nokia Network Routing Specialist II (NRS II) 4A0-112 Question # 3 Topic 1 Discussion
4A0-112 Exam Topic 1 Question 3 Discussion:
Question #: 3
Topic #: 1
Two IS-IS neighboring routers are trying to establish an adjacency, but the interface has been configured as broadcast on one of them and as point-to-point on the other. Why is the adjacency not established?
A.
The routers do not agree on the result of the DIS election.
B.
The routers discard the received Hello messages because they are not the expected type: LAN Hello vs point-to-point Hello.
C.
The routers do not receive each other’s Hello messages because they listen for messages transmitted to different multicast MAC addresses.
D.
The routers do not receive each other’s Hello messages because they listen for messages transmitted to different multicast IP addresses.
IS-IS routers use different types of Hello messages depending on whether the interface is configured as a broadcast (LAN) or point-to-point (P2P) link.
On a broadcast network (e.g., Ethernet), IS-IS routers use LAN Hello packets to establish adjacencies.
On a point-to-point link, IS-IS uses point-to-point Hello packets.
If one router is configured for a broadcast interface and the other for point-to-point, they will exchange incompatible Hello packets, and as a result, neither router will accept the other's Hello messages, preventing the adjacency from being established.
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