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Now there’s a lot of help available to you, in the Cisco Command Line Interface

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or CLI, the first one to remember is context sensitive help.

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Don’t forget that question mark is your friend.

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When in doubt, use the question mark to help you,

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it’s one of the best places to start.

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Type part of the command and press ? to view  the various options available to you.

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It’s important that you use the ? before asking or looking

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for help elsewhere because invariably it’s gonna help you

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and don’t forget to read the messages on the screen.

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Look at console errors that you receive, this will display for example

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incomplete commands or incorrect commands.

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I’ve shown a few of those already, if you don’t complete a command as an example.

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The router will warn you, if you type the incorrect command

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the router will warn you about that.

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So in these example, I’ve got cmd prompt open on my windows machine

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and I’m gonna telnet to my Cisco router.

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So I’m gonna telnet to the IP address of the router.

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I’m gonna log in with my password, sh ver

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shows me that this is an 1841 Cisco router running advance IP services.

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You can see here that it's an 1841 and if I use question mark once again

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notice I can see the various options available to me.

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If I type conf t notice I'm told that invalid input is detected at the current marker.

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If I try and type router ? notice I'm told that this is an unrecognized command.

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If I type e question mark (e ?) notice I get the options enable or exit.

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en question mark (en?) I get the option enable.

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en space question mark (en ?) I can run enable at different privileged levels.

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15 are full privileges which will allow me to do anything on the router.

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carriage return is enter, so I’m gonna do that option, in this example I’m told to enter

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an enable password, so a password has been configured on this router

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which requires me to enter it before going to enable or privilege mode.

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So I put my password in, lets use this command clock

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it's quite a nice one to show you the options.

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So if I type clock enter, incomplete command, see question mark

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clock is one of the options but if I type c enter, I’m told that it's an ambiguous command.

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cl question mark (cl?) there are still 2 matching entries clear or clock.

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clo tab, a command can now auto complete, question mark.

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I’ve got 3 options here, if I hit enter incomplete command.

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Up key or ctrl p to get the previous command back, question mark so I’m gonna use set

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as the option, question mark again, in this example I'll set it to 20:00:00 hours

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and I'll set it to the first of July 2015 question mark.

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Notice at this point I can hit carriage return

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if I get rid of the year and hit enter I’m told that's an incomplete command.

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Notice the question mark helps me at every step of the way

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it’s a good skill to learn, to use question mark and tab.

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so if I type c here, tab doesn’t work, co tab doesn’t work, con tab doesn’t work

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conf now I get configure, question mark

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You want terminal, press tab, so t tab completes the command

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Question mark tells me carriage return. Now I’m in global config mode.

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Router question mark, various routing protocols are available

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let's choose ospf and hit enter.

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I'm told it’s not a complete command. I need to specify a process id.

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Now I can hit enter or carriage return, now I’m taken to config router mode.

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Question mark shows me lots of options available within OSPF.

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let’s go for network

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I need to put my network command in.

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if I enter it as just 10, I'm told that it's incomplete, if I make a crazy

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network like that, I'm told it's unrecognized command, so it needs to be valid

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I need to put my wildcard mask in, OSPF uses what’s called an inverse mask.

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I’m told to put my area in, if I don’t, I'm told it’s an incomplete command.

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Hit enter now, incomplete command, so I have to say area and then specify

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an area and hit enter, control Zed, takes me back to privilege mode.

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The point is get used to using the question mark.

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Remember that some commands are valid but you have to be in the right mode.

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So if I type, router ospf 1 in privilege mode, that is not an accepted command.

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I'm in the wrong mode.

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Initially it may be confusing, you believe you're typing a correct command

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but the router doesn’t accept it, make sure you're in the right mode.

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So just because a command is not accepted doesn’t mean

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the command is incorrect, it could simply mean that you’re in the wrong mode.

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So check your mode, use question mark to help you and try again.