Cisco CCNA Preparation · lesson 10 of 36 · 25 min
Why Show Commands Matter
The CCNA exam heavily tests your ability to read and interpret show command output. These commands let you verify configuration, troubleshoot connectivity, and confirm that protocols are operating correctly — all without changing anything on the device.
Essential Show Commands
Reading Interface Status
Reading the Routing Table
The show ip route output uses codes to identify how each route was learned:
Flashcard Drill
show ip interface brief Quick summary of all interfaces: IP, line status, protocol status. up / up Interface fully operational — physical and data link layers both working. administratively down Interface was manually shut down — fix with no shutdown. show ip route Displays the routing table — shows all known networks and how they were learned. C in routing table Connected route — directly attached network. S in routing table Static route — manually configured. O in routing table OSPF route — learned via OSPF protocol. show mac address-table Shows the switch’s MAC address table — MAC to port mappings. show cdp neighbors Shows directly connected Cisco devices — device ID, port, platform. show vlan brief Shows VLAN names and which ports are assigned to each VLAN.
Knowledge Check
Show Commands — 10 Questions
An interface shows “administratively down / down”. What is the fix?
- Replace the cable
- Issue no shutdown on the interface
- Reload the device
- Check the routing table
Answer: Issue no shutdown on the interface
Administratively down means the shutdown command was issued. no shutdown re-enables it.
Which command shows a quick summary of all interface IPs and statuses?
- show interfaces
- show ip interface brief
- show running-config
- show version
Answer: show ip interface brief
show ip interface brief provides a compact table of interface name, IP, and up/down status.
In the routing table, what does the code “O” indicate?
- Connected route
- Static route
- OSPF route
- Default route
Answer: OSPF route
O = OSPF — the route was learned via the OSPF routing protocol.
An interface shows “up / down”. What does this indicate?
- Physical layer failure
- Physical OK but Layer 2 failing
- Interface is working normally
- Interface is administratively shut down
Answer: Physical OK but Layer 2 failing
up/down means the physical connection is good but Layer 2 (data link) is failing — often an encapsulation mismatch.
The routing table code for a directly connected network is _____.
Answer: C
C = Connected — the network is directly attached to one of the router’s interfaces.
Which command shows directly connected Cisco devices including their device ID and port?
- show arp
- show mac address-table
- show cdp neighbors
- show ip route
Answer: show cdp neighbors
show cdp neighbors uses Cisco Discovery Protocol to show directly connected Cisco devices.
Which command shows the switch’s learned MAC address to port mappings?
- show arp
- show mac address-table
- show ip route
- show vlan brief
Answer: show mac address-table
show mac address-table shows the switch’s CAM table — MAC addresses and the ports they were learned on.
show running-config displays the configuration saved in NVRAM.
- True
- False
Answer: False
show running-config shows the active config in RAM. show startup-config shows the NVRAM-saved config.
Which command shows VLAN names and port assignments on a switch?
- show interfaces trunk
- show vlan brief
- show mac address-table
- show cdp neighbors
Answer: show vlan brief
show vlan brief lists all VLANs, their names, and which ports are assigned to each.
The routing table code for a static route is _____.
Answer: S
S = Static — the route was manually configured with the ip route command.
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