Reading show ip route

Watch first

Plain-English explanation

show ip route is the router's forwarding map. Each line shows a prefix, administrative distance / metric, next-hop IP or exit interface, and how the route was learned (code letter).

If you can read this output fluently, half of routing troubleshooting is already done — you know whether the router even has a path.

Deep dive

Routing Ad — Administrative distance — lower is more trusted. OSPF = 110, static = 1, connected = 0.
From study charts · jdepew88 CCNA notes

Routing Protocols Comp Illustrated — Routing protocol comparison at a glance.
From study charts · jdepew88 CCNA notes

Common codes:

| Code | Meaning | |------|---------| | C | Connected | | S | Static | | O | OSPF | | D | EIGRP (know exists) | | R | RIP (legacy) | | * | Default route candidate |

Example line breakdown:

O    10.1.0.0/16 [110/20] via 192.168.1.2, 00:05:00, GigabitEthernet0/1

O = OSPF
[110/20] = AD 110, OSPF cost 20
via 192.168.1.2 = next-hop
GigabitEthernet0/1 = outgoing interface
Timer = route age

Connected example:

C    192.168.1.0/24 is directly connected, GigabitEthernet0/0

Gateway of last resort: 0.0.0.0/0 with S* or static default.

Step-by-step — read a small table

Gateway of last resort is 203.0.113.1 to network 0.0.0.0

C    10.10.10.0/24 is directly connected, Vlan10
L    10.10.10.1/32 is directly connected, Vlan10
S    192.168.0.0/16 [1/0] via 10.10.20.2
O    172.16.0.0/12 [110/30] via 10.10.20.2, 00:12:00, Vlan20
S*   0.0.0.0/0 [1/0] via 203.0.113.1

Questions:

How reach 172.16.5.5? → OSPF via 10.10.20.2
How reach 8.8.8.8? → Default via 203.0.113.1
Is 10.10.10.50 local? → Yes, connected /24

Commands to know

Routing table commands

show ip route show ip route ospf show ip route static show ip route connected show ip route 172.16.5.5

Troubleshooting

| Missing route symptom | Table tells you | |----------------------|-----------------| | No OSPF route | Adjacency or network statement issue | | Static present, not used | Better AD route exists — check LPM | | Only default for internal net | Missing specific route redistribution/advertisement | | Connected missing | Interface down or wrong IP |

Always check gateway of last resort line — confirms if default exists.

Exam relevance

Exam trap

L local host routes (/32) appear for router's own interface IPs on modern IOS — do not confuse with the connected subnet route C.

Metric meaning

OSPF uses cost; static often shows [1/0]. AD is first number — lower preferred across sources.

Practice checklist

Explain every field in five sample routing table lines
Given output, answer "which next-hop for X?" for ten IPs
Identify why a static route might not be used
Use routing table trainer tool for timed practice
Correlate connected interfaces with show ip int brief

In 'O 10.0.0.0/8 [110/50]', what does 110 represent?

Which code indicates a directly connected network?

Learning objectives