So by default on many IOS devices you can access via console cable or telnet, but telnet is not secure, luckily many cisco devices will support ssh, provided you set it up.
Note- some older devices don’t allow ssh. In my lab I didn’t have settings in any Catalyst 35xx devices or example.
I’ll break it down into the steps, if you have any of these already configured you can skip where you like.
Step 1 – Set a Hostname and domain.
The RSA key you will generate later needs a hostname and a domain since it’s a requirement.
Set a host name with: RTR(config)#hostname bob
Set a domain with: bob(config)#ip domain name bob.local
This would set the host+domain to bob.bob.local
Step 2 – Generate an RSA Key
The RSA key is the same as the SSL keys you exchange when you use a web page via https.
bob(config)#crypto key generate rsa general-keys
you will be prompted for the bit strength of the key and the default is 512. I use 1024, you can use more, keep in mind everything increases the larger you go.
If you already have a key you will be warned to overwrite it.
If you ever change the hostname or domain you will need to generate a new key.
Step 3 – Create a user with higher privilege.
You don’t actually have to use higher privilege, but I do, simply because you can use this with SDM should you wish to in that java hell, and because I don’t want to remember enable secrets because i’m lazy 😀
bob(config)#username bob privilege 15 secret Y0urM0m
bob is the username, the password is stored encrypted as Y0urM0m.
Step 4 – Setup your Virtual Terminals
bob(config)#line vty 0 15
bob(config-line)#transport input ssh.
This tells VTY to use the username you setup, and allows only ssh to be used over vty. It’s helpful to not close the Telnet session you have open while you test the ssh settings.. lest you forgot the password or well.. anything.. that would have you running to the device with a console cable.
I’m lazy.. I mean.. I’m really lazy. But hey.. that’s OK! I believe the best admins are the lazy ones, we plan for redundancy so it doesn’t bug us on weekends, we try to be efficient so we aren’t beating our heads against the walls to keep the bits flowing.. so.. it might not surprise you when I tell you that most of us IT people don’t understand binary. I’m going to sum up tho why maybe we all should.
What is Binary?
A quick description? If you’ve ever heard that all a PC understands is 1’s and 0’s.. that’s binary. But what you might not know is that this is a number system called Base 2, and using Binary you can represent any number in the system you ALREADY use which is called Base 10.
Why is Binary useful to you in IT?
The most immediate thing is Networking. All IP Addresses are a representation of Binary numbers, and yes I’m fully aware you might not need to know how it works.. but better network engineers know these things.. and so should you.
OK, give me some examples, but keep it small.
No Problem.. Binary isn’t just 1’s or 0’s. Each digit in binary is called a bit and each bit in binary each represents a value of 2x. To represent no value for that bit, you put a 0 no matter which place in binary you are in.
What does that mean? Lets start small, lets start with 2 bits.
in binary each place represents a value, from right to left. the first bit if it’s a 0 is 0 and if it’s a 1 it equals 1, which is 20
0 = 0
1 = 1
If we add a second bit, and it’s a 0 it still equals 0 but a 1 equals 2 which is 21
00 = 0
10 = 2
Now.. if they are both 1’s then it’s 2 + 1 which means that
11 = 3
so 3 becomes the maximum 2 bit number you can have in binary.
OK I’m ready for more.. lets go to 4 bits.
Ok.. you asked for it..
1st bit = 20 or 1
2nd bit = 21 or 2
3rd bit = 22 or 4
4th bit = 23 or 8
So if you had all ones in your binary number you’d add =
1 + 2 + 4 + 8 or 15 which is the maximum value of a 4 bit number. and if you wanted you could use 0 in there to represent any number that was between 0 and 15. Example: 10 in binary would be 1010 or 8 + 0 + 2 + 0, if you noticed the overused binary joke in the title, binary 10 is actually 2 or 2 + 0.
Although I’m not going to into Hex, Hex is a representation of 4 bit numbers. It’s 0 thru f which comes out to 16 (with 0 still being null) in a single character format. Once we move to IPV6 you will be using alot of Hex.
Why is this important in networking?
Because Binary is the foundation of IP addressing, if you’ve ever heard of CIDR notation (like a /24 or a /30 subnet) this is referring to binary. Although you are probably very familiar with DDN which is how IPV4 represents binary, subnetting in binary is very useful
Ok how do I learn more about Binary?
Ha.. google it. There a plenty of resources online about how binary works. If you ever want to get a networking cert, you will surely need to know it.
Here is just one of the videos I found on teh Youtubes that goes over binary.
the Command is: Get-mailbox -Organizationalunit "subdomain.domain.com/Users/BobsHouseofPizza" | get-mailboxstatistics | ft displayname,totalitemsize,lastlogontime > Bobshouse.txt
This creates a text file in whatever directory you are running in with the Exchange Shell, and the output will show, User’s Name, Size of User’s Mailbox, and the user’s last logon time, which is helpful if you are giving mail to external users and aren’t certain if they actually use that mail account.