# Using the no Version Versus the default Version of Commands

Most router configuration commands have a no version, which you can use to negate a command (or a portion of it specified by an optional keyword) or restore its default setting. When you use a command without the keyword no, you can reenable a disabled feature or override a default setting. You have the option of using the default keyword whenever the no keyword is also a choice; simply enter the keyword default instead of no.

In most cases, when you execute the default version of a command, it produces the exact results as the no version. There are some commands for which the default version yields a different result than the no version.

Commands for which the default behavior differs from the no behavior are clearly identified in this guide. Unless otherwise specified, therefore, the default command is identical to the no command and is neither documented nor discussed.

The syntax for each no command is described in this guide. Some commands do not have a no version; this is indicated in the individual command descriptions except for the show commands, none of which has a no version.

The CLI can act on no versions of commands when you have entered sufficient information to distinguish the command syntactically, and ignores all subsequent input on that line.

To be compatible with some non–E Series implementations, the no versions of commands accept the same options as the affirmative version of the commands. The CLI ignores the optional input if it has no effect on the command behavior. If using the option changes the behavior of the no version, the individual command entry in this guide describes the difference in behavior.