Examkin

Question

Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

A network administrator executes the command shown below to inspect the OSPFv2 configuration on interface GigabitEthernet0/0 of router R3 on a shared Ethernet segment:

text
R3# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.10.3/24, Area 0
Process ID 1, Router ID 192.168.10.3, Network Type BROADCAST, Cost: 1
State DROTHER, Priority 0
Designated Router (ID) 10.1.1.1, Interface address 192.168.10.1
Backup Designated Router (ID) 10.2.2.2, Interface address 192.168.10.2

If the current Designated Router (10.1.1.1) reboots and permanently disconnects from the network, which state will router R3 transition to following the OSPF election process?

  1. R3 will remain in the DROTHER state because an OSPF priority of 0 excludes the router from DR and BDR elections.Answer
  2. B
    R3 will automatically be promoted to Backup Designated Router (BDR) after the current BDR transitions to Designated Router (DR).
  3. C
    R3 will assume the Designated Router (DR) role because its Router ID is higher than the remaining operational routers.
  4. D
    R3 will trigger an election delay and shift the network type from BROADCAST to POINT_TO_POINT.

Answer

Router R3 will remain in the DROTHER state because an OSPF interface priority of 0 completely disables the router from participating in DR or BDR elections.
Configuring an OSPF priority of 0 on an interface ('ip ospf priority 0') explicitly prohibits the router from participating in Designated Router (DR) and Backup Designated Router (BDR) elections on multiaccess network segments. When the primary DR fails, the existing BDR becomes the new DR, but router R3 remains a DROTHER because its priority of 0 disqualifies it from election consideration regardless of its Router ID or interface IP.

Step-by-Step Solution

1
Analyze the CLI output for interface priority settings on router R3.
The CLI output displays 'State DROTHER, Priority 0' for interface GigabitEthernet0/0.
OSPF interface priority dictates election participation. Priority values range from 0 to 255.
2
Evaluate the effect of a priority 0 configuration during DR/BDR failover.
A priority of 0 (configured via 'ip ospf priority 0') strictly prevents the interface from becoming a DR or BDR.
Even when the existing DR fails and the current BDR moves up to DR, a router with priority 0 cannot participate in the election for the new BDR position.
3
Determine R3's resulting state after DR failover.
R3 stays in the DROTHER state while other eligible routers on the multiaccess segment contest the new BDR role.
Priority 0 overrides Router ID, Loopback IP addresses, and physical interface IP tie-breakers.

Key Concept

OSPFv2 DR/BDR Election Rules and Priority 0 Exclusion
Rate this question

Topics

OSPFv2 Network Types and DR/BDR Selection

More questions from this topic