Refer to the exhibits. All links inside the network are configured at a default cost of one inside the fully converged OSPF domain. Given the configuration from XR1, which interface does traffic from

Question

Exhibits

Options

• AInterface GigabitElhemet 0/0. The tie breaker of the node index priority is lower and trumps the
• BInterface GigabitEthernet 0/1. The tie breaker of the path cost being lower. The node index
• CInterface GigabitEthernet 0/1. The tie breaker of the node index priority is lower and trumps the
• DInterface GigabitEthernet 0/0. The tier breaker of the path cost being lower. The node index

• A
  76% (38)
• B
  4% (2)
• C
  6% (3)
• D
  14% (7)

Explanation

When all OSPF links have equal cost (cost = 1), multiple equal-cost paths may exist to a destination. OSPF uses tie-breaking rules to select among equal-cost paths. In Cisco IOS XR with Segment Routing or standard OSPF ECMP, when path costs are equal, the tie-breaker mechanism applies. The node index (or router ID) is used as a secondary criterion - a lower node index/priority value takes precedence. GigabitEthernet 0/0 leads toward the path whose next-hop router has a lower node index than the path via GigabitEthernet 0/1. Since the node index (a stable, deterministic identifier in SR-OSPF) for the path through Gi0/0 is lower, OSPF selects Gi0/0 as the exit interface. This is consistent with how Cisco IOS XR breaks ECMP ties in SR-enabled OSPF domains - lower node index wins when path costs are identical.

No community discussion yet for this question.