This document is publicly accessible at http://bit.ly/ickl-networking-101 

Networking 101 with *nix Command Line Tools

SSH - remote secure shell access

NC - the networking swiss army knife

TELNET - play around with line-based protocols

LSOF - who is having my ports?

DIG - troubleshoot your DNS

TRACEROUTE - find out how your packets are moving about

PING - i think almost everyone knows this

Python Tools

Web Server

Mail Server

Debugging Server

Proxy Server

SSH - remote secure shell access

• shell access into remote machines

• with password authentication
• w/o password authentication

• Use ~/.ssh/config to create “aliases”
• ssh-keygen

• using ssh-add cmd line
• secured with password
• without password

• ssh-add

• ssh-agent and how it works with ssh

• ssh agent forwarding

• ssh -A to do ssh agent forwarding

• using scp

• honours items in ~/.ssh/config 

• ssh proxy with ssh -D 
• create ssh tunnels with ssh -L 

NC - the networking swiss army knife

• connect to machines

• nc IP_ADDRESS PORT_NO

• create temporary fake server

• nc -l PORT_NO

• can use it for ssh proxy command
• only supports 1 connection at a time

TELNET - play around with line-based protocols

$ telnet smtp.gmail.com 25

$ telnet google.com 80

LSOF - who is having my ports?

$ lsof -i :PORT_NUMBER

DIG - troubleshoot your DNS

$ dig -t ANY infinite-code.com

$ dig -t ANY www.infinite-code.com

TRACEROUTE - find out how your packets are moving about

$ traceroute infinite-code.com

NOTES:

• * means timed out
• the time indicated per hop shows the total amount of time for the packet to reach that hop, each hop is tested 3 times

PING - i think almost everyone knows this

$ ping google.com

PING google.com (173.194.120.97): 56 data bytes

64 bytes from 173.194.120.97: icmp_seq=0 ttl=57 time=41.138 ms

64 bytes from 173.194.120.97: icmp_seq=1 ttl=57 time=43.198 ms

64 bytes from 173.194.120.97: icmp_seq=2 ttl=57 time=41.232 ms

64 bytes from 173.194.120.97: icmp_seq=3 ttl=57 time=44.689 ms

…

--- google.com ping statistics ---

86 packets transmitted, 85 packets received, 1.2% packet loss

round-trip min/avg/max/stddev = 39.464/42.280/78.773/6.608 ms

Python Tools

Web Server

Has been in standard library for a long time. Instantly host the contents in the folder you can the command, by default port 8000, you can change the port if needed.

# runs on port 8000

$ python -m SimpleHTTPServer

# if you want to run on another port

$ python -m SimpleHTTPServer 8001

Mail Server

Debugging Server

Doesn’t really send out the mail. Just print out in stdout/console.

$ python -msmtpd --class DebuggingServer --debug -n

Simple tutorial on SMTP commands:

• http://www.canturkisci.com/ETC/C_unix_etc/smtp_tutorial.htm

Proxy Server

Print out in stdout/console and relay to real mail server.

$ python -msmtpd --debug -n