show config

5.4 Troubleshooting Tools

Basic Network Device Commands

📘CompTIA Network+ (N10-009)

---

What is show config?

• The show config command is a network device command used on devices like routers, switches, and firewalls.
• Its purpose is to display the current configuration of the device.
• It is a read-only command, meaning it does not change anything on the device—it only shows information.

Think of it as opening a device’s settings to see what is currently set up.

---

Where is it used?

• On routers and switches (Cisco, Juniper, HP, etc.).
• Typically in Command Line Interface (CLI) mode.
• Helps network administrators troubleshoot network problems or verify configurations.

---

What does show config display?

When you run show config, you can see:

1. Device Hostname
   • The name of the device on the network.
   • Example: Router1 or Switch2.
2. Interface Settings
   • Shows all the interfaces (ports) on the device.
   • Includes IP addresses, subnet masks, and status (up or down).
   • Example: FastEthernet0/1 is up, line protocol is up IP Address: 192.168.1.1 /24
3. Routing Information
   • Displays routing protocols that are configured (e.g., OSPF, RIP, EIGRP).
   • Shows static routes and dynamic routing settings.
4. VLAN Configuration
   • On switches, it shows VLANs (Virtual LANs) and which ports belong to which VLAN.
   • Example: VLAN 10 - Sales VLAN 20 - IT
5. Access Control Lists (ACLs)
   • Shows any security rules applied to the device, like allowing or blocking traffic.
   • Example: permit ip 192.168.1.0 0.0.0.255 any deny ip any any
6. Other Device Settings
   • Default gateways
   • SNMP settings
   • Passwords or login configurations
   • Any other special configurations applied to the device

---

Why is show config important?

1. Troubleshooting
   • Helps identify if a device misconfiguration is causing network issues.
   • Example: If an interface is down or an IP address is incorrect.
2. Verification
   • Before making changes, network admins can check the current configuration.
   • Ensures new changes won’t conflict with existing settings.
3. Documentation
   • Useful for network documentation and auditing.
   • Network teams often export the configuration using this command.

---

How to use it?

1. Log into the device via CLI.
2. Enter privileged mode if needed: enable
3. Type the command: show config
4. Review the output carefully:
   • Check interfaces, VLANs, routing, ACLs, etc.
   • Look for errors or misconfigurations.

---

Example Output on a Router:

hostname Router1
!
interface FastEthernet0/0
 ip address 192.168.1.1 255.255.255.0
 no shutdown
!
interface FastEthernet0/1
 ip address 10.0.0.1 255.255.255.0
 shutdown
!
router ospf 1
 network 192.168.1.0 0.0.0.255 area 0
!
line vty 0 4
 login local
!
end

What you can learn from this:

• Router name → Router1
• Interface status → FastEthernet0/0 is active, 0/1 is shutdown
• IP addresses → 192.168.1.1 and 10.0.0.1
• Routing protocol → OSPF configured for 192.168.1.0/24

---

Exam Tips for CompTIA Network+

1. Remember: show config shows the current running configuration of the device.
2. Distinguish it from show running-config or show startup-config:
   • show running-config → currently active configuration in RAM
   • show startup-config → saved configuration in NVRAM
   • Some vendors use show config as a shortcut or alias.
3. Focus on troubleshooting:
   • Be able to read and interpret interfaces, IP addresses, VLANs, and routing information.
4. Multiple-choice questions may ask:
   • Which command helps verify interface IP addresses? → show config
   • Which command allows checking ACLs applied? → show config
5. Remember the command does not modify the device—it is read-only.

---

✅ Summary in Simple Terms

• Command: show config
• Purpose: Displays current device configuration.
• Use: Troubleshoot, verify, and document device settings.
• Shows: Hostname, interfaces, IPs, routing, VLANs, ACLs, and other settings.
• Exam Focus: Recognize what the command shows and how it helps troubleshoot networks.