5.4 Troubleshooting Tools
Basic Network Device Commands
📘CompTIA Network+ (N10-009)
What is show route?
The show route command is a network device command used on routers (and some Layer 3 switches) to display the device’s routing table.
- A routing table is like a map that the router uses to know where to send packets to reach different networks.
- Every router needs a routing table to make forwarding decisions. Without it, the router wouldn’t know where to send data.
Purpose of show route
The main purposes of using show route are:
- Check routes – See which networks the router knows about.
- Troubleshoot connectivity – Verify if a route to a certain network exists.
- See route types – Identify if a route is learned statically (manually) or dynamically (via routing protocols like OSPF, EIGRP, or RIP).
How the output looks
When you run show route, you typically see something like this (simplified example):
O 192.168.1.0/24 [110/2] via 10.0.0.1, 00:00:12, FastEthernet0/0
C 10.0.0.0/24 is directly connected, FastEthernet0/0
S 172.16.0.0/16 [1/0] via 10.0.0.2
Let’s break this down:
- Route Code
O→ OSPF-learned routeC→ Connected network (directly attached to a router interface)S→ Static route (manually configured)
- Network and Mask
- Example:
192.168.1.0/24 - Shows the destination network the route points to.
- Example:
- Next-hop / Outgoing Interface
- Example:
via 10.0.0.1, FastEthernet0/0 - This shows where to send packets to reach the network.
- Example:
- Metric / Cost
- Example:
[110/2] - This is used by the router to choose the best route when multiple routes exist. Lower numbers are preferred.
- Example:
- Uptime / Age
- Example:
00:00:12 - Shows how long the route has been in the table. Useful for troubleshooting.
- Example:
Types of routes you’ll see in show route
| Route Type | Description |
|---|---|
| Connected (C) | Networks directly attached to the router interface. These are always available. |
| Static (S) | Manually configured routes. Admin decides exactly where traffic should go. |
| Dynamic (R, O, D, B) | Learned via routing protocols (RIP, OSPF, EIGRP, BGP). They update automatically. |
| Default Route (S*) | A route used when there is no specific match in the routing table. Usually points to 0.0.0.0/0. |
Exam tip: Know the difference between static, dynamic, and connected routes. The
show routecommand helps you verify all three.
Practical IT usage examples (non-car analogies)
- Troubleshooting a network segment
- A user can’t reach
192.168.10.0/24. - Run
show routeon the router. - If there’s no route, the router cannot forward packets. You may need to add a static route or check your dynamic routing protocol.
- A user can’t reach
- Checking routing protocol operation
- If using OSPF, you can see
Oroutes in the table. - If expected networks don’t appear, the OSPF configuration might have a problem.
- If using OSPF, you can see
- Verifying default routes
- All traffic destined for unknown networks goes through the default route (
0.0.0.0/0). show routeconfirms if the default route is configured correctly.
- All traffic destined for unknown networks goes through the default route (
Key Points for the CompTIA Network+ Exam
- Command name:
show route - Purpose: Displays the router’s routing table.
- Important to know:
- Route types (connected, static, dynamic, default)
- How to identify next hop and outgoing interface
- How routing protocols are represented (e.g., OSPF → O, RIP → R, EIGRP → D, BGP → B)
- Metrics and preference values indicate which route is preferred
- Common troubleshooting scenarios:
- Missing route → packets cannot reach destination
- Wrong next-hop → misrouted traffic
- Multiple routes → router chooses the lowest metric
Quick Exam Memory Aid
C = Connected
S = Static
R = RIP
O = OSPF
D = EIGRP
B = BGP
Tip: Always check your routing table first before troubleshooting network connectivity.
