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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

An engineer inspects the OSPFv2 operational status of interface GigabitEthernet0/0 on router R1 using the `show ip ospf interface` command:

text
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.1.10/24, Area 0
Process ID 1, Router ID 192.168.1.10, Network Type BROADCAST, Cost: 1
State DROTHER, Priority 0
Designated Router (ID) 10.3.3.3, Interface address 192.168.1.3
Backup Designated Router (ID) 10.2.2.2, Interface address 192.168.1.2

If the active Designated Router (10.3.3.3) reboots and leaves the network, which role will router R1 assume?

  1. A
    R1 will become the new Backup Designated Router because its interface IP address is higher than that of the current BDR.
  2. R1 will remain in the DROTHER state and will not participate in the election for Designated Router or Backup Designated Router.Answer
  3. C
    R1 will preempt the Backup Designated Router and immediately become the new Designated Router.
  4. D
    R1 will become the new Designated Router while the current Backup Designated Router retains its BDR role.

Answer

Router R1 will remain in the DROTHER state and will not participate in the election for Designated Router or Backup Designated Router.
In OSPFv2 broadcast multiaccess networks, setting an interface priority to 0 completely disables DR/BDR election eligibility for that interface. Even if the current DR fails and a new election occurs, any router with a priority of 0 remains strictly in the DROTHER state.

Step-by-Step Solution

1
Analyze the output of the 'show ip ospf interface' command for router R1.
Interface GigabitEthernet0/0 has an OSPF priority set to 0 ('Priority 0').
OSPF interface priority determines eligibility for DR and BDR roles during elections on multiaccess networks.
2
Apply OSPF DR/BDR election rules regarding priority values.
A router interface configured with an OSPF priority of 0 (ip ospf priority 0) is ineligible to become a DR or BDR.
Setting priority to 0 forces the router interface to remain in the DROTHER state indefinitely regardless of router ID, IP address, or failures of existing DR/BDR routers.
3
Determine the outcome when the active DR fails.
The current BDR (10.2.2.2) promotes to DR, and R1 remains a DROTHER, taking no part in any subsequent BDR election.
R1 is excluded from all DR/BDR election calculations due to its priority of 0.

Key Concept

OSPF Priority 0 Exclusion from DR/BDR Selection
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Topics

OSPFv2 Network Types and DR/BDR Selection

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