Cisco Switch Commands
Step 7 of 888%

Safe Config Changes

Most of this lab is about looking safely. This page shows how to verify known-good trunk and access-port settings before making any changes. The supplied PKT and config files are the source of truth; do not change them just because this page shows what change commands look like.

After this page, you should be able to:

  • Verify the known-good SW2 port roles before touching configuration
  • Recognize trunk and access VLAN configuration
  • Understand shutdown and no shutdown
  • Save running config to startup config intentionally

Confirm the port role before changing it

Open SW2, go to the CLI tab, and get to SW2#. Before you change a port, prove what is connected to it. In the known-good lab, Fa0/1 is the trunk to SW1, Fa0/2 is PC1, and Fa0/3 is PRINTER1.

show interfaces status
show cdp neighbors detail
show logging

If CDP says Fa0/1 is connected to SW1, that confirms the known-good trunk role. Do not convert Fa0/1 into an access port.

Verify Fa0/1 is the upstream trunk

Stay on SW2#. The known-good config uses Fa0/1 as the trunk to SW1. Verify that state; do not change it.

show interfaces trunk
show running-config

Expected result: Fa0/1 appears as a trunk and allows VLANs 10 and 20. In show running-config, find interface FastEthernet0/1 and confirm it has switchport mode trunk plus switchport trunk allowed vlan 10,20.

Verify PRINTER1 is already in the printer VLAN

Stay on SW2#. PRINTER1 belongs on FastEthernet0/3 as an access port in VLAN 20. Verify that state before assuming the printer is patched incorrectly.

show interfaces status
show running-config

Expected result: Fa0/3 has the name Printer1 and shows VLAN 20 in show interfaces status.

In the known-good SW2 config, interface FastEthernet0/3 contains description Printer1, switchport access vlan 20, and switchport mode access.

This is what a correct printer access port looks like. In a real environment, only change a VLAN after documentation or a ticket proves the current VLAN is wrong.

Verify PC1 is in the user VLAN

Stay on SW2#. PC1 belongs on FastEthernet0/2 as an access port in VLAN 10. This gives you a known-good access port to compare against the printer port.

show interfaces status
show running-config

Expected result: Fa0/2 has the name PC1, shows VLAN 10, and its running config has switchport mode access.

shutdown and no shutdown

Stay on SW2#. This example shows what the commands look like, but do not run them in the known-good lab unless you intentionally want to practice a link bounce. In a real network, this can disconnect someone.

configure terminal
interface fastEthernet0/3
shutdown
no shutdown
end

shutdown administratively disables the port. no shutdown brings it back. Bouncing the wrong uplink is an outage, so verify the interface from more than one source before using these.

After no shutdown, Packet Tracer may print link up/down messages over your prompt. If you are still at SW2(config-if)#, type end once to return to SW2#. If you already see SW2#, do not type end again.

Save config on purpose

Stay on SW2#. Save only after you verify the change is correct. In Packet Tracer, use one save method. The first method asks a follow-up question; press Enter to accept the default filename.

copy running-config startup-config

When Packet Tracer asks Destination filename [startup-config]?, press Enter. Do not type write memory at that prompt.

Or, if you prefer the shorter save command, run this by itself from SW2#:

write memory

If a change should survive reboot, save it. If you save a bad change, the bad change survives reboot too. The real skill is knowing when to save and when to roll back.

A professional change note should say whether the config was saved. “Verified and saved” means something different from “verified for lab practice only; not saved.”

Safe change checklist: confirm hostname, confirm interface from two sources, capture current config, make one focused change, verify service works, and save only if the change is correct.

Checkpoint

  • You can correct lab-only access port settings and verify them.
  • You can identify access VLAN commands.
  • You can explain why saving config is an intentional decision.

Hands-On Practice

Verify the known-good port roles from the supplied configs, then decide whether any change is actually needed.

Your checklist and answers are saved locally in this browser.

Pre-Change Verification

Run show interfaces status or show interfaces trunk on SW2 and find the trunk toward SW1.

Verify The Known-Good State