One of the most powerful things about Python is its ability to iterate over ANYTHING as if it were a list. Lists, tuples, dictionaries, and even strings can all be iterated quickly and elegantly. Python also introduces a concept known as list comprehension which allows you to do rather complex filtering of list contents within a single statement.

To illustrate how awesome and powerful list comprehension is, let’s start with a basic example that is NOT using it:

>>> mylist = [1,2,3,4,5]
>>> for item in mylist:
...     if item % 2 == 0: print item, 'is an even number.'
...
2 is an even number.
4 is an even number.

>>> mylist = [1,2,3,4,5]
>>> evens = []
>>> for item in mylist:
...     if item % 2 == 0: evens.append(item)
...
>>> evens
[2, 4]

Why list comprehension rocks With list comprehension, the logic that isolates the even numbers and the declaration of the list that will capture this output are compressed into a single statement:

>>> mylist = [1,2,3,4,5]
>>> evens = [i for i in mylist if i % 2 == 0 ]
>>> evens
[2, 4]

So list comprehensions at their most basic level allow for compression of code and streamlining of logical statements. Advanced usage of list comprehension can get pretty silly, but then so can nested loop statements.  It supports nesting as many statements as you can throw at it so longs as they are syntactically correct.

If you find yourself coding shit like this:

>>> losers = ['Joe','Jim','Jon','Jen']
>>> for u in losers:
...     if u.startswith('J'):
...             if u.endswith('n'):
...                     if u != 'Jon':
...                             print u
...
Jen

>>> [u for u in losers if u.startswith('J') and u.endswith('n') and u != 'Jon']
['Jen']

Could be a melon, but looks like a co-co-nut.

So, there comes a time in a man’s life when people at work on the inside network need to access things on the internet.  This is called “proxying”.  Yes, yes, I know; very fascinating.  These secure machines on the inside network don’t have access to the internet by design (See RFC 1918).  It’s the most basic layer of obfuscation (a 25 cent word we use a lot in the security world) and protection from bad internet traffic, not including firewalls and all that other exciting stuff.

Ok so we want to let our secure hosts on the inside proxy SSH to the internet via our SOCKS server.

Assumptions:

• A Unix/Linux machine with the latest version of netcat installed (assumed to be found at /usr/bin/nc).  All modern operating systems have this.  Stop whining.
• A SOCKS proxy listening on TCP port 1080.
• A remote internet server listening for SSH connections on TCP port 22.
• You know what ~ means.  (Hint:  It’s shorthand for your home directory.)

Create an entry in ~/.ssh/config. If this file doesn’t exist, create it. If it does, add this shit to the bottom:

Host proxythatshit
    ProxyCommand /usr/bin/nc -X 5 -x proxy.whatever.com:1080 internet.com 22

% ssh proxythatshit
jathan@proxythatshit's password:
[jathan@internet.com]~%

A little breakdown:

ProxyCommand /usr/bin/nc -X 5 -x proxy.whatever.com:1080 internet.com 22

• ProxyCommand: An OpenSSH directive that tells SSH how to proxy the connection
• /usr/bin/nc: The path to the netcat binary and the ProxyCommand in question here.  Proxying is one of the many things netcat does.
• -X 5: Tells netcat to use SOCKS version 5
• -x proxy.whatever.com:1080: Tells netcat to proxy the connection using proxy.whatever.com on port 1080
• internet.com 22: The name and port of the destination we’re trying to get to by way of the proxy

You may be asking yourself, “Why not just use an HTTP proxy?”  Because HTTP proxies tend to be very picky about allowing you to proxy non-HTTP connections to destination ports other than the one you connected to.  In other words, if the proxy is listening on port 8080, good luck proxying a connection that isn’t HTTP (such as this SSH proxy thing) on anything other than port 80, 443, or 8080 it probably won’t work. If you’re using mod_proxy, it absolutely will not work.  Don’t ask me why.  It just doesn’t.  Squid might work, but it is a pain in the ass to setup.

There you have it.  Don’t blame me if you get fired because you were looking at a picture of a monkey fucking a coconut for the 52 seconds it took to read this.

It’s simple:

netscreen(M)-> set admin user nocadmin password abc123 privilege read-only

% ssh nocadmin@netscreen
nocadmin@netscreen's password:
For Authorized Use Only, Violators Will Be Prosecuted.
netscreen(M)->

netscreen(M)-> ?
exit                 exit command console
get                  get system information
mtrace               multicast traceroute from source to destination
ping                 ping other host
trace-route          trace route
netscreen(M)->