200-301 · Question #591
Refer to the exhibit. Router R1 resides in OSPF Area 0. After updating the R1 configuration to influence the paths that it will use to direct traffic, an engineer verified that each of the four Gigabi
The correct answer is B. GigabltEthornet0/1. When multiple equal-cost paths exist to a destination, a router typically performs per-flow load balancing; however, if a single path must be deterministically chosen, routers may prefer the path with the numerically lowest next-hop IP address.
Question
Refer to the exhibit. Router R1 resides in OSPF Area 0. After updating the R1 configuration to influence the paths that it will use to direct traffic, an engineer verified that each of the four Gigabit interfaces has the same route to 10.10.0.0/16. Which interface will R1 choose to send traffic to reach the route?
Exhibits
Options
- AGigabitEthernet0/0
- BGigabltEthornet0/1
- CGigabitEthernet0/2
- DGigabitEthernet0/3
How the community answered
(48 responses)- A13% (6)
- B54% (26)
- C27% (13)
- D6% (3)
Why each option
When multiple equal-cost paths exist to a destination, a router typically performs per-flow load balancing; however, if a single path must be deterministically chosen, routers may prefer the path with the numerically lowest next-hop IP address.
While GigabitEthernet0/0 is the first interface, routers do not automatically prefer it over others in ECMP unless its next-hop IP is the lowest, or specific load-balancing logic directs traffic there.
In Equal-Cost Multi-Path (ECMP) scenarios where all paths have the same OSPF cost, if a single interface must be deterministically chosen for a routing decision (e.g., for internal processes or a specific display order), Cisco routers often prefer the path with the numerically lowest next-hop IP address, which we assume corresponds to GigabitEthernet0/1 in this case.
This interface would only be chosen if its corresponding next-hop IP address was the lowest among the options, which is not universally the case or specified.
This interface would only be chosen if its corresponding next-hop IP address was the lowest among the options, which is not universally the case or specified.
Concept tested: OSPF ECMP tie-breaking logic
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/15-mt/iro-15-mt-book/iro-ospf-ecmp.html
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