Two copies of the configuration
| Name | Lives in | What it is |
|---|---|---|
| running-config | RAM (memory) | What the router is doing right now. Every command you type changes it at once. |
| startup-config | NVRAM (memory that survives power-off) | What the router loads when it starts up. |
RAM is emptied when the router restarts. So until you save, your changes only live in the running-config, and a reload or power cut throws them away.
Saving
copy running-config startup-config (short: copy run start) saves. The router asks for a file name and suggests [startup-config]: just press Enter. write memory (wr) does the same job and is still widely used.
In NetLab
▶ R1 Router>enable Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#hostname HQ HQ(config)#end *Mar 1 00:00:04.000: %SYS-5-CONFIG_I: Configured from console by console HQ#copy running-config startup-config Destination filename [startup-config]? Building configuration... [OK] HQ#show startup-config | include hostname hostname HQ
Watch unsaved work disappear
Here a change is made but not saved, and the router is reloaded. When it asks Save? [yes/no] we answer no:
In NetLab
▶ R1 Router>enable Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#hostname BRANCH BRANCH(config)#end *Mar 1 00:00:04.000: %SYS-5-CONFIG_I: Configured from console by console BRANCH#reload System configuration has been modified. Save? [yes/no]: no Proceed with reload? [confirm] Reloading... VulnTech NetLab router restarting... No startup-config found: starting with the factory configuration. Press RETURN to get started!
After the reload the prompt is back to Router>: the hostname was never saved.
Useful commands
| Command | What it does |
|---|---|
show running-config | Show the live configuration |
show startup-config | Show the saved configuration |
copy running-config startup-config | Save |
reload | Restart the router (it offers to save first if something changed) |
erase startup-config | Delete the saved configuration (back to factory settings after the next reload) |
Remember: Change it, check it works, then save it. A router that is fixed but not saved is only fixed until the next power cut.