A Cisco router is configured to run OSPFv2 without an explicitly configured manual router … — Cisco CCNA

A Cisco router is configured to run OSPFv2 without an explicitly configured manual router ID. The router has the following active interface IP addresses:

- Loopback0: $10.10.1.1/32$
- Loopback1: $10.20.1.1/32$
- GigabitEthernet0/0: $192.168.1.254/24$
- GigabitEthernet0/1: $172.16.50.1/24$

Which IP address will OSPFv2 select as the router ID?

$10.20.1.1$ Answer
B
$192.168.1.254$
C
$10.10.1.1$
D
$172.16.50.1$

Answer

The OSPFv2 router ID selected by the router is

10.20.1.1

In OSPFv2, when a router ID is not manually specified with the 'router-id' command, the router selects the highest IPv4 address among all active loopback interfaces. Comparing Loopback0 (

10.10.1.1

) and Loopback1 (

10.20.1.1

10.20.1.1

is the highest loopback IP address and is selected as the OSPF Router ID.

Step-by-Step Solution

Check for an explicitly configured manual OSPF Router ID

No manual 'router-id' command is present.

Manual configuration takes highest precedence in OSPF Router ID election.

Evaluate active loopback interfaces

Two active loopbacks exist: Loopback0 (

10.10.1.1

) and Loopback1 (

10.20.1.1

If no manual router ID is specified, OSPF evaluates active loopback interfaces next.

Select the highest IP address among active loopback interfaces

Compare

10.20.1.1

and

10.10.1.1

;

10.20.1.1

is numerically higher.

OSPF selects the highest active loopback IP address over lower loopbacks and over any physical interfaces.

Key Concept

OSPFv2 Router ID Election Precedence

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