Quiz Entry - updated: 2026.07.14
How does a router use the show ip route command output to forward packets?
The show ip route output displays all known routes with their source codes, destination networks, prefix lengths, next-hop addresses, and exit interfaces. The router searches this table for each packet's destination IP (Internet Protocol) using longest prefix match.
Reading the routing table output:
R1# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
Gateway of Last Resort is not set
C 192.168.1.0/24 is directly connected, GigabitEthernet0/0
L 192.168.1.1/32 is directly connected, GigabitEthernet0/0
Route codes and what they mean:
| Code | Source | How Learned |
|---|---|---|
| C | Directly Connected | Interface with IP is up/up |
| L | Local | /32 host route for router's own interface IP |
| S | Static | Manually configured by admin |
| O | OSPF (Open Shortest Path First) | Learned dynamically via OSPF |
| D | EIGRP (Enhanced Interior Gateway Routing Protocol) | Learned dynamically via EIGRP |
| R | RIP (Routing Information Protocol) | Learned dynamically via RIP |
| B | BGP | Learned dynamically via BGP |
| S* | Default Static | Gateway of last resort (0.0.0.0/0) |
Tip: Routers use the routing table like a map to find the best path for a given destination. The more specific the route (longer prefix), the more preferred it is.
Go deeper:
Routing table (Wikipedia) — the fields (destination/netmask, next hop, interface, metric) the output renders.