200-301 · Question #1541
Refer to the exhibit. How will the device handle a packet destined to IP address 100.100.100.100?
The correct answer is D. It will choose the route with the longest match,. When a router forwards a packet, it determines the best path by first identifying the most specific route in its routing table.
Question
Exhibits
Options
- AIt will always prefer the static route over dynamic routes and choose the route
- BIt will choose the route with the lowest metric,
- CIt will choose the route with the highest metric,
- DIt will choose the route with the longest match,
How the community answered
(60 responses)- A10% (6)
- B2% (1)
- C7% (4)
- D82% (49)
Why each option
When a router forwards a packet, it determines the best path by first identifying the most specific route in its routing table.
Administrative distance is a tie-breaker used when multiple routes to the same destination have the same longest prefix match, it is not the initial or sole determinant.
The lowest metric is considered only after the longest prefix match and administrative distance criteria have been applied to distinguish between equally preferred routes from the same routing protocol.
A route with the highest metric is never preferred; the lowest metric is always chosen when comparing routes from the same routing protocol to the same destination.
When a device needs to forward a packet, it consults its routing table and prioritizes routes based on the longest prefix match. This means it selects the route that has the most specific network address matching the destination IP address, regardless of administrative distance or metric initially.
Concept tested: Router packet forwarding logic (Longest Prefix Match)
Source: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/23602-27.html#anc7
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