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I'm trying to figure out what characters the Cisco router doesn't like when creating a password or pre-shared key. Please help me understand this. Thank you.

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    It should be noted: Don't use characters in your password that cannot be entered where you are asked for a password. For example, tab is bad choice from a web browser. – Ricky Jan 6 '15 at 1:32
  • I like to use this password generator to make random passwords and pre-shared keys because it lets you define what to exclude. – Stone G. Jan 7 '15 at 1:00
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Generally, the characters ? and [space] are the only il-advised characters. The ? indicates you are asking for help. The space indicates you are done with the password and moving onto the next command.

You should avoid @ and ! since they could interfere with other commands as you type them.

For IOS, username (user) password 0 ... everything to the end-of-line is the password - literally, even a "blind" trailing space! For an ASA, username (user) password "..." everything inside the quotes is the password. (ctrlv will allow the input of ? on both platforms) (the use of quotes allows use of spaces, but then excludes the use quotes in the password)

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    username foo pass 0 foo bar has a password of foo(space)bar. everything after 0 is the password. If you can type it, it's part of the password. ("foo bar" means the quotes are part of the password too.) – Ricky Jan 5 '15 at 22:54
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    I once ran across a trick question about how to include a "?" in hostnames and passwords. Typing (as I remember it) a Ctrl-V allows the use of "?" and other special characters where you normally couldn't use them. – Ron Maupin Jan 5 '15 at 23:12
  • Ricky that may be true on a router but on a firewall after the space are more options like priv settings. For instance this would set the pass to 12345 and set priv to 15. username test password 12345 priv 15 – Stone G. Jan 5 '15 at 23:36
  • tested with asa v9.2.1. The handling of backslash is simply broken. – Ricky Jan 6 '15 at 1:27
  • In switches that use IOS you cannot have a space. The backslash worked fine for me in ASA v9.3.1. – Stone G. Jan 6 '15 at 1:38

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