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Hack Like A Pro: Networking Basics For The Aspiring Hacker, Part 1 by jimklef(m): 9:02pm On Jan 08, 2016 |
Welcome back, my greenhorn hackers!
As expected with Null Byte's dramatic
growth over the last year, we have added
many new aspiring hackers who are still
lacking in the basics of networking. In
addition, with the new "White Hat"
certifications coming out shortly, the exam
will require some basic networking skills
and knowledge to pass.
As a result, I decided to offer my own take
on networking basics to make certain that
everyone here has these basic skills down,
which I consider foundation skills for
hacking. In reality, without basic networking
and Linux skills, hacking will certainly remain
beyond your reach.
I will attempt to address at least one basic
networking skill in each of these tutorials. In
this one, I want to address some of the
basics of IP addresses, NAT, DHCP, and ports.
IP Addresses
Internet Protocol addresses (IP addresses)
makes the world go 'round. Or, at least,
enable us to email, Skype, and navigate the
web. It's almost as important as the world
going around!
Each digital device (computer, laptop, phone,
tablet, etc.) is assigned an IP address, and
this is what enables us to communicate and
connect with it. Imagine an IP address as
similar to your house address. Without that
address, no one could find you and send
you snail mail.
The IP address system we are presently
using is known as IP version 4, or IPv4 (we'll
address the upcoming IPv6 in a coming
tutorial). It is made up of 32 bits of four
octets, or four groups of 8 bits (on/off
switches).
For instance, 192.168.1.101. Each of the
numbers between the periods (.) is the
decimal equivalent of 8 bits. This means that
we calculate the base 2 number that
computers use represented by the 8 bits
and convert them to decimal numbers that
humans are more accustomed to working
with (see the diagram below). Each one of
the octets (8 bits) is capable of representing
numbers within the range 0 through 255 (2
to the 8th power).
Classes of IP Addresses
IP addresses are generally put into three
classes, and the ranges are:
Class A: 0.0.0.0 - 127.255.255.255
Class B: 128.0.0.0 - 192.255.255.255
Class C: 192.0.0.0 - 223.255.255.255
In a future tutorial, we will address
subnetting and subnet masks that vary with
these different IP classes.
Public vs. Private IP Addresses
It's important to note that our IP address
system has its limitations. The biggest
limitation is that there are not enough IP
addresses to cover all of the devices that
need to connect to the internet. The IPv4
system that we are working with now has
only 4.3 billion IP addresses. With 7.3 billion
people on the planet and far more devices,
that certainly is not enough.
As a result, a system was developed to reuse
a group of IP addresses to be used within a
LAN—and are not usable over the internet.
These addresses can be used over and over
again within each local area network, but
not over the internet, thereby conserving
the number of IP addresses necessary to
keep the world going 'round.
These private addresses include:
192.168.0.0 - 192.168.255.255
10.0.0.0 - 10.255.255.255
172.16-.0.0 - 172.16.255.255
You have probably seen the private IP
addresses beginning with 192.168.Bleep.Bleep
or 10.Bleep.Bleep.Bleep on your Kali system when
you type ifconfig.
This is your private IP that is only usable on
the local area network. To communicate
over the internet, it must be translated to a
public IP by a NAT device (see NAT below).
DHCP
Dynamic Host Configuration Protocol (DHCP)
assigns IP addresses dynamically. This
means that you do not have the same IP
address all of the time. Most of the time,
these IP address assignments are on a local
area network. Remember, on LANs we use
private IP addresses. When each device is
connected to the LAN, it must request an IP
address. That device sends that request to
the DHCP server that then assigns an IP
address to that system for a fixed length of
time known as a "lease."
Each time you connect to the LAN, you are
likely to receive a different (dynamic) IP
address, but usually in the same range. For
instance, 192.168.0.0 - 192.168.255.255.
NAT
Network Address Translation (NAT) is
protocol whereby internal private IP
addresses are "translated" to an external
public IP address that can be routed
through the internet to its destination.
Remember, private IP addresses of the
systems inside the LAN cannot use their IP
addresses on the internet because they are
not unique (every LAN uses basically the
same IP addresses inside their network).
The NAT device accepts requests to traverse
the internet from an internal machine. It
then records that machine's IP address in a
table and converts the IP address to the
external IP address of the router. When the
packet returns from its destination, the NAT
device looks into its saved table of the
original request and forwards on the packet
to the internal IP address of the system that
made the original request within the LAN.
When working properly, the individual
systems and users don't even realize this
translation is taking place.
For instance, the diagram above shows two
phones with private IP addresses behind a
device that is serving as both a NAT device
and a router (not uncommon). The devices
use their private IP addresses within the
LAN, but when they want to communicate
over the internet, the NAT device translates it
to one of the 4.3 billion public IP addresses
that are unique on the internet. In this way,
the routers along the way know exactly
where to send the packets.
Ports
Ports are a kind of subaddress. The IP
address is the primary address and the port
is the subaddress. Using a well-worn, but
effective metaphor, think of the IP address
as the street address of a building and then
the port as the apartment number. I need
the street address to get to the right
building, but I need the apartment address
to find who I am looking for. This is the
same with ports. The IP address gets us to
right machine, but the port takes us to
correct service, say HTTP on port 80.
There are 65,536 (2 raised to the 16th
power) ports. The first 1,024 are generally
referred to as the common ports. People
obviously don't remember all 65,536 ports
(unless they are savant), or even the 1,024
most common ports. As a hacker, security
engineer, and/or network engineer, though,
there are a few ports that you should know
by heart:
20 FTP
21 FTP
22 SSH
23 Telnet
25 SMTP
53 DNS
69 TFTP
80 HTTP
88 Kerberos
110 POP3
123 NTP
135 Microsoft's RPC
137-139 Microsoft's NetBIOS
143 IMAP
161 SNMP
389 LDAP
443 HTTPS or HTTP over SSL
445 SMB
500 IKE
514 syslog
3389 RDP
I will be following up with additional
tutorials on networking soon (with topics
on subnetting, IPv6, TCP/IP, and more) in the
near future, so keep coming back, my
greenhorn hackers! Hack like a pro part @www.mullerwaparz.tk 2 Likes 1 Share |
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