A banner is more than just a little cool—one very good reason for having a banner is to give any and all who dare attempt to telnet or dial into your internetwork a little security notice. And you can create a banner to give anyone who shows up on the router exactly the information you want them to have. Make sure you’re familiar with these four available banner types: exec process creation banner, incoming terminal line banner, login banner, and message of the day banner (all illustrated in the code below):
Router(config)#banner ?
LINE c banner-text c, where 'c' is a delimiting character
exec Set EXEC process creation banner
incoming Set incoming terminal line banner
login Set login banner
motd Set Message of the Day banner
Message of the day (MOTD) is the most extensively used banner. It gives a message to every person dialing into or connecting to the router via Telnet or auxiliary port, or even through a console port as seen here:
Router(config)#banner motd ?
LINE c banner-text c, where 'c' is a delimiting character
Router(config)#banner motd #
Enter TEXT message. End with the character '#'.
$ Type your motd banner here.
#
Router(config)#^Z
Router#
00:25:12: %SYS-5-CONFIG_I: Configured from console by console
Router#exit
Router con0 is now available
Press RETURN to get started.
For example, you can set a banner on one line as shown:
Router(config)#banner motd x Unauthorized access prohibited! x
This example will work just fine, but if you add another MOTD banner message
they would end up on a single line.
Below are some details of the other banners I mentioned:
Exec banner You can configure a line-activation (exec) banner to
be displayed when an EXEC process (such as a line-activation or incoming
connection to a VTY line) is created. By simply starting a user exec session
through a console port, you’ll activate the exec banner.
Incoming banner You can configure a banner to be displayed on terminals
connected to reverse Telnet lines. This banner is useful for providing
instructions to users who use reverse Telnet.
Login banner You can configure a login banner to be displayed on
all connected terminals. This banner is displayed after the MOTD banner,
but before the login prompts. The login banner can’t be disabled
on a per-line basis, so to globally disable it, you’ve got to delete
it with the no banner login command.
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