Similar to the OSPF DR, the IS-IS DIS needs to be elected on a broadcast network. However, the OSPF DR is preemptive by default, whereas the IS-IS…

The statement incorrectly describes the preemption characteristics of the OSPF Designated Router (DR) and the IS-IS Designated Intermediate System (DIS). The OSPF DR election process is non-preemptive. Once a DR is elected on a broadcast segment, it will not be replaced by another router that comes online later with a higher priority. A new DR election only occurs if the existing DR or Backup Designated Router (BDR) fails. Conversely, the IS-IS DIS election is preemptive. If a new router joins the broadcast network with a higher priority than the current DIS, it will preempt the existing DIS and take over the role. The statement reverses these fundamental behaviors.

The statement is evaluated as "False" because its core claim about the preemption behavior of both protocols is factually incorrect. The "True" option is wrong because it would validate the flawed assertion that OSPF DR is preemptive and IS-IS DIS is non-preemptive, which is the opposite of their actual operation.

1. Huawei HCIP-Datacom-Core Technology V1.0 Training Material.

Document: HCIP-Datacom-Core Technology V1.0 Training Material.pdf

Section on OSPF DR Election: In the chapter covering OSPF principles

the material explains the DR/BDR election. It states

"The DR/BDR election is not preemptive. If a new router with a higher priority is added to the network after the DR/BDR election is complete

the DR and BDR will not be re-elected." (Paraphrased from typical content in OSPF sections).

Section on IS-IS DIS Election: In the chapter covering IS-IS principles

the material details the DIS election mechanism. It clarifies

"The DIS election is preemptive. If a new router with a higher priority is added to a broadcast network

a new DIS will be elected immediately." (Paraphrased from typical content in IS-IS sections). This highlights the key difference in preemption between the two protocols.

2. RFC 2328 - OSPF Version 2.

Section: 9.4. Electing the Designated Router.

Content: The RFC describes the election algorithm based on the Wait Timer. The election process runs when there is a change in the set of neighbors on the network

but it does not specify a preemption mechanism. The established behavior is that once the DR and BDR are selected

they hold their roles until they fail

confirming the non-preemptive nature of the election.

3. ISO/IEC 10589:2002 - Intermediate system to Intermediate system intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473).

Section: 7.3.6. Designated Intermediate Systems.

Content: The standard specifies that the Intermediate System (IS) with the highest isPriority is elected as the DIS. This check is continuous. If an IS with a higher priority becomes active on the LAN

it will assume the DIS role

which defines a preemptive election process.