show running-config – Current Configuration Guide

Purpose of show running-config

Definition: show running-config (or show run) is a Cisco IOS command used to display the current active configuration in RAM on a router, switch, or firewall.

  • Shows all settings currently in effect.
  • Critical for troubleshooting, verification, documentation, and audits.

Difference: Running-Config vs. Startup-Config

Aspect Running-config Startup-config
Location RAM (volatile) NVRAM (non-volatile)
Purpose Live/active config (affects device instantly) Backup loaded at next reload/reboot
Persistence Lost after reload if not saved Remains until overwritten
How to View show running-config show startup-config
Tip: Always save running-config to startup-config after making changes using:
copy running-config startup-config

Structure of Running Configuration

  • Global Settings: Hostname, domain, logging, enable secret/passwords
  • Interface Configurations: IP, VLAN, speed/duplex, shutdown/no shutdown
  • Routing Protocols: OSPF, EIGRP, RIP, BGP, etc.
  • Access Control Lists: Permit/deny rules (numbered/named)
  • VLAN & Switching: VLAN definitions, spanning-tree, EtherChannel
Sample Output: 
hostname HQ-Router
!
interface GigabitEthernet0/0
 ip address 10.10.1.1 255.255.255.0
 no shutdown
!
interface GigabitEthernet0/1
 ip address 192.168.1.1 255.255.255.0
 shutdown
!
router ospf 1
 network 10.10.1.0 0.0.0.255 area 0
!
access-list 10 permit 192.168.1.0 0.0.0.255
!
line vty 0 4
 password 7 070C285F4D06
 login

Interpreting Key Sections

SectionPurpose/ContentExample
Global Hostname, domain, logging, SNMP, enable secret 
hostname BranchRouter
ip domain-name example.com
enable secret 5 $1$mERr$...
Interfaces IP, VLAN, shutdown, speed/duplex, access-group 
interface Vlan10
 ip address 10.1.10.1 255.255.255.0
 no shutdown
Lines Console, VTY access, passwords 
line vty 0 4
 password cisco
 login
ACLs Security rules (permit/deny) 
access-list 100 deny ip any 10.1.20.0 0.0.0.255
access-list 100 permit ip any any
Routing Protocols OSPF, EIGRP, RIP, BGP 
router ospf 10
 network 10.1.10.0 0.0.0.255 area 0

Navigating and Filtering Large Configurations

  • Use SPACE for next page, ENTER for next line.
  • Disable paging: terminal length 0
  • Search/filter with pipelines:
    • show run | include ospf (only lines containing 'ospf')
    • show run | begin interface (start at matching line)
    • show run | section interface GigabitEthernet0/1 (show config section)

Saving, Exporting, and Backing Up Configurations

  • Save to startup-config: copy running-config startup-config
  • Export to TFTP/FTP/SCP: copy running-config tftp: (for backups or sharing)
  • Schedule automated backups: Use kron or network management tools (see below).
Kron Example – Daily TFTP Backup at 3:00 AM 
kron policy-list backup-config
 cli copy running-config tftp:
exit
kron occurrence daily-backup at 3:00 recurring
 policy-list backup-config
exit

Making and Managing Configuration Changes

  • All changes in configuration mode (conf t) apply instantly to running-config.
  • Changes are NOT persistent after reboot unless saved to startup-config.
  • Common edits: IP address assignment, VLAN membership, password change, ACL modification.
Best Practice: After any major change, always save config and document who/what/when/why.

Security Considerations

  • Sensitive data is visible: passwords (unless encrypted), SNMP communities, keys, etc.
  • Use enable secret for strong encryption instead of enable password.
  • Avoid hardcoding passwords—use AAA (RADIUS/TACACS+) when possible.
  • Restrict access to configuration files and use secure protocols for export (SCP, SFTP).

Best Practices

  • Always save changes (copy running-config startup-config).
  • Automate regular backups to external servers.
  • Document all configuration changes for audit and troubleshooting.
  • Use filtering/searching to efficiently review large configs.

Example: Troubleshooting with show running-config

Scenario: John cannot access the server at 10.1.10.100 from his PC (different VLANs, routed by L3 switch).
  1. Check interface configs: 
    show running-config | section interface
    • Ensure correct IP/subnet, not shutdown, proper VLAN.
    • Example: 
      interface Vlan10
 ip address 10.1.10.1 255.255.255.0
 no shutdown
!
interface Vlan20
 ip address 10.1.20.1 255.255.255.0
 shutdown
      Analysis: Vlan20 is shutdown—devices in VLAN 20 cannot route traffic.
      Action: no shutdown on Vlan20.
  2. Check routing protocols: 
    show running-config | section router
    • Verify all required networks are advertised.
    • Example: 
      router ospf 10
 network 10.1.10.0 0.0.0.255 area 0
      Analysis: VLAN 20 not included—add network 10.1.20.0 0.0.0.255 area 0.
  3. Check ACLs: 
    show running-config | include access-list
    show running-config | section interface
    • Are ACLs applied that block traffic?
    • Example: 
      interface Vlan10
 ip access-group 100 in
!
access-list 100 deny ip any 10.1.20.0 0.0.0.255
access-list 100 permit ip any any
      Analysis: ACL 100 denies all to VLAN 20—remove/adjust as needed.
  4. Save and document: 
    copy running-config startup-config

Exam Tips and Key Points

  • show running-config reveals all active settings—including unsaved changes.
  • Distinguish running-config (live/volatile) vs. startup-config (persistent).
  • Use filtering (| section, | include) for efficient troubleshooting.
  • Protect sensitive config data (passwords, SNMP, keys).
  • Always save configs after changes and automate backups.
  • Document all changes—essential for audits and troubleshooting.

Show Running-Config Command Quiz

1. What does the show running-config command display?

Correct answer is A. The running-config is the active configuration stored in RAM that the device is currently using.

2. What is the main difference between running-config and startup-config?

Correct answer is D. Running-config is live config in RAM; startup-config is stored in NVRAM and loaded at boot.

3. Which command is used to save the running configuration to the startup configuration?

Correct answer is B. This command copies the live running-config into startup-config to persist changes.

4. In the running configuration, where would you expect to find interface IP addresses and shutdown commands?

Correct answer is C. Interface IPs and shutdown commands are found under each interface's config block.

5. What can the show running-config | include command do?

Correct answer is A. The pipe and include filter output to lines with the keyword.

6. What is a potential security concern when viewing the running configuration?

Correct answer is D. Running-config may contain sensitive info like passwords, requiring protection.

7. Which of these commands backs up the running configuration to an external TFTP server?

Correct answer is B. This copies the current running-config to the TFTP server for backup.

8. What must you do after making changes in configuration mode to ensure they persist after a reboot?

Correct answer is C. To save config changes permanently, copy running-config to startup-config.

9. How can you view the configuration specific to the VTY lines using the running config?

Correct answer is A. The pipe and section filter show the config starting at the vty section.

10. Which statement about changes in running-config is true?

Correct answer is D. Running-config changes are live but must be saved to persist after reboot.

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