os_script_network_and_ssh – https://www.ais-lab.eu

Network

On Unix systems you can get and configure the network from the command line.
There are also some commands, to test and analyze the local connections.

Pinging a host and outputing the results:
```
> ping 
```
This sends ECHO Requests to the specified HOST.
Usefull for:
1. to see if a system is available on the network
2. to check if the network is configured correct.
  The command:
```
> ping www.hsrw.eu
```
Will check if your computer can resolve the domain www.hsrw.eu to an ip
and then it will check if there is a system with that IP.
Listing ip addresses of all network interfaces:
1. Compatible on nearly all unix based systems:
```
> ifconfig
```
2. On reasonable modern linux systems:
```
> ip addr
```
Getting routing information:
Routing, determines which interface to use to send and recieve traffic
1. Unix systems:
  - IPv4
```
> netstat -rn
```
  Hint: -r means: show routing table, -n show information as numbers,
  the last part is sometimes important, to avoid additional DNS request and
  response waits.
- IPv6
```
> netstat -f inet6 -rn
```
1. Linux systems:
  - IPv4
```
> ip route
```
- IPv6
```
> ip -6 route
```
Display of all active listening ports:
```
> netstat -pnltu
```
Fetching whois information for domain:
```
> whois domain
```
Fethcing DNS information for domain:
```
> dig domain
```
Downloading a file:
```
> wget file
```
Curl is a command line tool used to transfer data using any supported protocols
As default, curl will output the response it got to the command line
```
> curl option domain
```
Example:
```
> curl https://www.hochschule-rhein-waal.de/en
> curl ftp://ftp.example.com/file[1-20].jpeg
```

SSH

SSH or Secure Shell is used to securely gain command line access to systems
over non secure networks.

Connection to a host as a user:
```
> ssh user@host
```
- Example:
```
> ssh pi@192.168.0.70
```
Connection to a host on specific port as a user:
```
> ssh -p port user@host
```
In order to enable a passwordless login you can use:
This will copy the public key of the local ssh id to a special file
authorized_keys in .ssh/ of the home folder of the user

HINT: This requires that the next command was done before
```
> ssh-copy-id user@host
```
SSH is able to use a private/public cryptographic key-pair for
authentication.
To generate such a key-pair, the following command can be used:
```
> ssh-keygen -b 4096
```
This will generate a 4096 bit length RSA key.
It will also ask for a password to secure the key.

Goodies

Network

SSH

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