To revive a Cisco router that is unable to boot up normally, the router has to be in stable condition such as in ROMMON mode as first step. Once the router crashes, it may not enter ROMMON mode, keeps trying to boot up normally to no avail, and constantly loops. In some cases, the router crashes after being up for years and left untouched. When you have installed the wrong IOS (or one that is too big to fit into the router memory), the router may crash or boot to the ROMMON (ROM Monitor) prompt. * Router has been configured not to boot up normally at all (one-in-the-million case)Ī router entering ROMMON mode is considered simple situation to remedy since it means of stable router configuration and of simple procedure to revive. * Router crashes suddenly out of the blue (rare case) * Router tries to boot up IOS image that is too big to fit into its DRAM (not that typical case) * Router has been configured to boot from media that does not exist (less common case) * Valid IOS image file has gone missing, deleted, or corrupted (common case) The cause could be either one of the following When you notice your router won't boot normally and goes to ROMMON mode (showing the rommon prompt), it means that basically the router can't find a valid IOS image to boot from. This FAQ assumes some knowledge of running basic IOS commands, setting up TFTP servers, some IP network understanding, and physical/hardware troubleshooting.įollowing are typical cases in regards of router inability to boot up normally.ĭeleted/Corrupted/Wrong Type/No IOS image and Router goes to ROMMON mode

This FAQ has been brought to help those that are unfamiliar around Cisco image troubleshooting process.Īlthough this FAQ has been written mostly for Cisco routers, the concept applies to other Cisco devices such as switches and firewalls. As you console in to the router, you do not see IOS prompt at all instead it is either looping or there is this ROMMON prompt. As network administrator, you may encounter issue of a Cisco router won't boot up normally.

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