An enterprise router has populated its IPv4 routing table with the following entries:
text
D 10.50.0.0/16 [90/2560512] via 10.1.1.1, 01:12:40, GigabitEthernet0/0
O 10.50.12.0/24 [110/20] via 10.1.1.2, 00:45:12, GigabitEthernet0/1
S 10.50.12.80/28 [1/0] via 10.1.1.3
S 10.50.12.80/29 [250/0] via 10.1.1.4
The router receives a packet with a destination IP address of . Which next-hop IP address will the router select to forward this packet?
- 10.1.1.4Answer
- B10.1.1.3
- C10.1.1.1
- D10.1.1.2
Answer
10.1.1.4 via the longest prefix match route 10.50.12.80/29
When a router processes a packet destination address, it searches the routing table for all matching network prefixes and selects the route with the longest prefix length (most specific mask). The destination address 10.50.12.85 falls within the range 10.50.12.80 - 10.50.12.87 defined by 10.50.12.80/29. Because /29 is longer than /28, /24, and /16, the router forwards the packet using the next-hop 10.1.1.4 regardless of its high administrative distance value of 250.
Step-by-Step Solution
Key Concept
Longest Prefix Match (LPM) rule in IPv4 routing decision logic
Estimated Time:1m 15s