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IOS keeps two copies of its config: the running one in RAM (live, editable, volatile) and the startup one in NVRAM (loaded at boot, persistent). Every config change you make goes into running-config immediately. Whether it survives a reboot depends entirely on whether you've copied it to startup-config.
| Location | Volatility | View with | Persist with |
|---|---|---|---|
| running-config (RAM) | Lost on reload/power loss | `show running-config` | N/A — live copy |
| startup-config (NVRAM) | Persists across reboots | `show startup-config` | `copy run start` / `write mem` |
! Save running-config to startup-configR1-HQ# copy running-config startup-configDestination filename [startup-config]?Building configuration...[OK]! Equivalent short formR1-HQ# write memory! View both configsR1-HQ# show running-configR1-HQ# show startup-config! Erase startup-config (factory reset on next reload)R1-HQ# erase startup-configErasing the nvram filesystem will remove all configuration files! Continue? [confirm][OK]
`erase startup-config` is destructive. It wipes the config in NVRAM. The running config is still live until you reload — but as soon as you reload, the device comes up blank. Save a copy somewhere before running this, always.
! Back up running-config to a TFTP serverR1-HQ# copy running-config tftp:Address or name of remote host []? 10.10.20.50Destination filename [r1-hq-confg]? r1-hq-backup-2026-01-15.cfg!!1234 bytes copied in 0.856 secs (1442 bytes/sec)! Restore from TFTPR1-HQ# copy tftp: running-configAddress or name of remote host []? 10.10.20.50Source filename []? r1-hq-backup-2026-01-15.cfgDestination filename [running-config]?Accessing tftp://10.10.20.50/r1-hq-backup-2026-01-15.cfg...Loading r1-hq-backup-2026-01-15.cfg from 10.10.20.50 (via GigabitEthernet0/1): ![OK - 1234 bytes]
`copy tftp: running-config` merges the file into the current running config — it doesn't replace it. If the device already has config, the merge can produce unexpected results. To load a clean config, `erase startup-config`, reload, then `copy tftp: running-config`.
When a router boots: it loads the IOS image from flash, then looks for startup-config in NVRAM. If found, it applies that config to become the running-config. If NVRAM is empty, it drops into the setup dialog — a wizard for initial configuration that most engineers skip via `no` at the first prompt.
Configuration lifecycle mastered. Next lesson covers CLI productivity features you'll use daily.
Finish the lesson once you have worked through the material. This awards ★ 30 XP.