HCIP-Datacom H12-821_V1.0 Exam Questions and Answers PDF

Understanding DIS Election in IS-IS:

On an IS-IS broadcast network, a Designated Intermediate System (DIS) is elected to create and update pseudonodes for efficient communication.

The election is based on the following criteria:

DIS Priority: The router with the highest priority is elected as the DIS.

Router ID (tie-breaker): If priorities are equal, the router with the highest Router ID is elected.

Analyzing the DIS Priorities and Router IDs:

R1: Priority = 64, Router ID = 1.1.1.1

R2: Priority = 1, Router ID = 2.2.2.2

R3: Priority = 127, Router ID = 3.3.3.3

R4: Priority = 10, Router ID = 4.4.4.4

Among the routers, R3 has the highest DIS priority (127), making it the DIS.

Correct Option:

Option B (R3): Correct, as R3 has the highest priority.

Option A (R1): Incorrect, as its priority is lower (64).

Option C (R4): Incorrect, as its priority is lower (10).

Option D (R2): Incorrect, as its priority is the lowest (1).

References:

HCIA-Datacom Study Guide, Chapter: IS-IS DIS Election

Huawei IS-IS Configuration and DIS Role Details

When OSPF routers have interfaces on different network segments with different subnet masks, the network type can be adjusted to establish adjacency. A point-to-point (P2P) network type eliminates the requirement for matching subnet masks by treating the link as directly connected without intermediate devices.

P2P Network Characteristics

OSPF treats the link as a direct connection between two routers.

No DR/BDR election occurs, simplifying adjacency establishment.

Subnet mask differences do not hinder neighbor relationships as the link is viewed as a logical tunnel.

HCIP-Datacom-Core Reference

The OSPF configuration section explicitly mentions P2P as a suitable network type for resolving adjacency issues caused by mismatched subnet masks​​.

 BGP Route Flapping and Mitigation

While route flapping is a concern in large-scale networks, BGP employs mechanisms such as Route Dampening to mitigate its impact. Route dampening suppresses frequently flapping routes for a period of time to reduce resource consumption and network instability.

Therefore, it is incorrect to state that the issue cannot be resolved in BGP.

 HCIP-Datacom-Core Reference

The mechanism of route dampening is detailed in the BGP optimization chapters​​.

When OSPF routers exchange LSDBs using Database Description (DD) packets, they first establish a master-slave relationship. The router with the larger Router ID becomes the master, setting the MS (Master/Slave) bit in the DD packets. This hierarchical relationship ensures an orderly exchange of routing information ​.