Refer to the following routing table excerpt from a Cisco router:
text
O 10.20.0.0/16 [110/50] via 172.16.1.1, 01:12:35, GigabitEthernet0/0
D 10.20.10.0/24 [90/307200] via 172.16.2.1, 00:45:10, GigabitEthernet0/1
S 10.20.10.128/25 [1/0] via 172.16.3.1
A packet arrives at the router destined for host IP address 10.20.10.130. Which two statements correctly describe how the router evaluates its routing table components to forward this packet? (Select two.)
- The router forwards the packet using the static route (10.20.10.128/25) because /25 is the longest matching prefix for destination 10.20.10.130.Cevap
- BThe router selects the EIGRP route (10.20.10.0/24) because EIGRP has a lower administrative distance (90) than OSPF (110).
- The router evaluates prefix length prior to checking administrative distance or metric when making forwarding decisions.Cevap
- DThe router forwards the packet via GigabitEthernet0/0 because OSPF routes override static routes in the routing table.
Cevap
The router selects the static route (10.20.10.128/25) because /25 is the longest matching prefix for destination 10.20.10.130, and the router evaluates prefix length prior to checking administrative distance or metric when making forwarding decisions.
When forwarding a packet, a Cisco router first identifies all routes that match the destination IP address and selects the route with the longest prefix length (most specific subnet mask). Since 10.20.10.128/25 matches destination 10.20.10.130 with 25 matching network bits, it is selected over the /24 and /16 routes. Administrative distance and metrics are only evaluated during route selection when prefix lengths are identical.
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Longest Prefix Match Rule in Cisco Routing Tables