A Cisco router's IPv4 routing table contains four active static routes to various destination networks:
- `ip route 0.0.0.0 0.0.0.0 192.168.1.4`
- `ip route 10.10.0.0 255.255.0.0 192.168.1.1`
- `ip route 10.10.4.0 255.255.255.0 192.168.1.2`
- `ip route 10.10.4.16 255.255.255.240 192.168.1.3 110`
When the router receives an IP packet destined for , which next-hop IP address will the router select to forward the packet?
- 192.168.1.3Answer
- B192.168.1.2
- C192.168.1.1
- D192.168.1.4
Answer
192.168.1.3 is selected because 10.10.4.16/28 provides the longest matching subnet mask for the destination address 10.10.4.25.
When a router makes a packet forwarding decision, it compares the destination IP address () against all installed routes in its routing table and selects the route with the most specific match (longest subnet mask). The destination address falls into the subnet ( to ). Since is longer than , , and , the router selects this entry and forwards the packet to next-hop . Administrative Distance is irrelevant during the actual lookup phase of already-installed routes.
Step-by-Step Solution
Key Concept
Longest Prefix Match forwarding decision logic in IPv4 Routing