CyberCertPrepNetwork FundamentalsSwitching & Routing BasicsEASYFree question
A routing table has the following entries for traffic destined to 10.1.5.75: Route A: 10.0.0.0/8, Route B: 10.1.0.0/16, Route C: 10.1.5.0/24, Route D: 0.0.0.0/0. Which route is selected, and what principle determines this?
- A.Route C (10.1.5.0/24) - Longest Prefix Match: /24 is the most specific route that includes 10.1.5.75
- B.Route A (10.0.0.0/8) - Class A routes have highest priority in classful routing
- C.Route D (0.0.0.0/0) - default routes always take priority
- D.Route B (10.1.0.0/16) - the router selects routes alphabetically
Why A is correct
Longest Prefix Match (LPM): all four routes match 10.1.5.75, but the router selects the one with the most prefix bits (most specific match). /8 = 8 bits match. /16 = 16 bits match. /24 = 24 bits match. /0 = 0 bits match (matches everything). /24 wins with the highest prefix length. This is fundamental to IP routing - without LPM, specific routes within larger blocks would be unreachable. The default route (0.0.0.0/0) is the LEAST specific and is only selected when no more specific route exists.
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