Copying an IOS Image to a Server:
You want to save a backup copy of your IOS image on a TFTP server.
You can upload a copy of your router’s IOS image to a TFTP server with the following set of commands:
Before attempting to upgrade the IOS version of a router it’s a good idea to save a copy of the current IOS image. This way, if an upgrade fails or if you have problems with the new IOS version, you can revert back to the old proven IOS version.The only real difference is the size of the file involved, since IOS images are quite a bit larger than configuration files.
you have to watch out for the file permissions on your TFTP server. The transfer will fail if this file isn’t world writable. We highly recommend that you remove the world-writable attribute on this file after uploading it. On Unix systems, you can use the chmod command to change the file attributes. This will ensure that the file isn’t accidentally overwritten. Unlike configuration files, which you should never store in your TFTP directory, IOS images pose no security concerns, as long as they are not world writeable.