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Zorluk: OrtaOSPFv2 Network Types and DR/BDR Selection

During a scheduled maintenance window, a network specialist examines the OSPFv2 operational status of interface GigabitEthernet0/1 on router R3 using the Cisco IOS CLI:

text
GigabitEthernet0/1 is up, line protocol is up
Internet Address 10.1.1.3/24, Area 0
Process ID 1, Router ID 192.168.100.1, Network Type BROADCAST, Cost: 1
State DROTHER, Priority 0
Designated Router (ID) 10.1.1.1, Interface address 10.1.1.1
Backup Designated Router (ID) 10.1.1.2, Interface address 10.1.1.2

If both the current Designated Router (10.1.1.1) and Backup Designated Router (10.1.1.2) suffer a simultaneous power failure, which role will router R3 assume on this multiaccess segment after the network re-converges?

  1. A
    R3 will assume the Designated Router (DR) role because its Router ID (192.168.100.1) is higher than any other router on the segment.
  2. R3 will remain in the DROTHER state and will be ineligible to become either the DR or BDR.Cevap
  3. C
    R3 will automatically become the Backup Designated Router (BDR) while the next eligible router with a non-zero priority becomes the DR.
  4. D
    R3 will dynamically change its OSPF network type to Point-to-Point to bypass the DR/BDR election process.

Cevap

R3 will remain in the DROTHER state and will be ineligible to become either the DR or BDR.
In OSPFv2 broadcast network types, setting an interface OSPF priority to 0 makes that interface permanently ineligible to become a Designated Router (DR) or Backup Designated Router (BDR). Even if all active DR/BDR routers fail, an interface configured with priority 0 remains in the DROTHER state and will never be promoted, regardless of how high its Router ID is.

Adım Adım Çözüm

1
Analyze the CLI output for OSPF interface state and priority setting.
The CLI snippet displays 'State DROTHER, Priority 0' for interface GigabitEthernet0/1 on R3.
An OSPF interface priority value of 0 explicitly configured on an interface signifies that the router is disqualified from DR and BDR elections.
2
Evaluate the impact of active DR and BDR router failures on R3.
Even though both the DR and BDR fail, R3 cannot participate in the re-election due to its priority value of 0.
Router ID parameters (such as 192.168.100.1) are only evaluated among routers with an interface priority of 1 or higher.
3
Determine R3's final state post-convergence.
R3 remains a DROTHER router and forms adjacency only with the newly elected DR and BDR.
disqualification rule for priority 0 is absolute on broadcast multiaccess OSPF networks.

Anahtar Kavram

OSPFv2 DR/BDR Ineligibility via Priority 0
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Konular

OSPFv2 Network Types and DR/BDR Selection

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