|
IP ADDRESS
STRUCTURE:
Note: the terms multicast address and MSB are explained at
the end.
Every station on a PSN (packet switched network) that is
based on the TCP/IP protocol (your computer is one, for example.
Yes, we're referring to a host that is connected to the net) must
have an IP address, so it can be identified, and information can be
relayed and routed to it in an orderly fashion.
An IP address consists of a 32 bit logical address. The
address is divided into two fields:
1) The network
address:
Assigned by InterNIC (Internet Network Information Center).
In fact most ISPs (internet service providers) purchase a
number of addresses and assign them individually.
2) The host
address:
An address that identifies the single nodes throughout the
network. It can be assigned by the network manager, by using
protocols for it such as DHCP, or the workstation itself. [The IP
networking protocol is a logically routed protocol, meaning that
address 192.43.54.2 will be on the same physical wire as address
192.43.54.3 (of course this is not always true. It depends on the
subnet mask of the network, but all of that can fill a text of its
own)
IP address structure:
---.---.---.---
^ ^
| |
network | host
Every " --- " = 8 bits.
The first bits ===> network address
The last bits ===> host address.
with 8 bits you can present from 0-255 . (binary=(2 to the
power of 8)-1)
Example:
11000010.01011010.00011111.01001010 (binary)
194.90.31.74 (decimal)
IP address CLASSES :
We can classify IP addreses to 5 groups. You can
distinguish them by comparing the "High Order" bits (the first four
bits on the
left of the address):
type | model | target | MSB |addr.range |bit number|
max.stations|
| | groups | | |net./hosts| |
------|--------|--------|-----|--------------|----------|-------------|
A |N.h.h.h | ALL | 0 | 1.0.0.0 | 24/7 | 16,777,214 |
| | ACCEPT | | to | | |
| | HUGE | | 127.0.0.0 | | |
| | CORPS | | | | |
-----------------------------------------------------------------------
|N.N.h.h | TO ALL | 10 | 128.1.00 | 16/14 | 65,543 |
B | | LARGE | | to | | |
| | CORPS | | 191.254.00 | | |
-----------------------------------------------------------------------
|N.N.N.h |TO ALOT | 110 | 192.0.1.0 | 8/22 | 254 |
C | |OF | | to | | |
| |SMALL | | 223.225.254 | | |
| |CORPS | | | | |
-----------------------------------------------------------------------
D | NONE |MULTI-CA|1110 | 224.0.0.0 | NOT FOR | UNKNOWN |
| |ST ADDR.| | to | USUAL | |
| |RFC-1112| |239.255.255.255| USE | |
-----------------------------------------------------------------------
E | NOT FOR|EXPERIME|1,1,1,1| 240.0.0.0 |NOT FOR| NOT FOR
USE|
| USE |NTAL | | to |USE | |
| |ADDR. | |254.255.255.255| | |
-----------------------------------------------------------------------
N=NETWORK , h=HOST .
Notice the address range 127.X.X.X. These addresses are
assigned to internal use to the network device, and are used as an
application tool only. For example: 127.0.0.1, the most common one,
is called the loopback address - everything sent here goes directly
back to you, without even traveling out on the wire. Also, some IPs
are reserved for VPNs - Virtual Private Networks. These are local
area networks over wide area networks that use the Internet Protocol
to communicate, and each computer inside the network is assigned
with an IP address. So, suppose a certain computer wants to send a
data packet to another host on the network with the IP 'x', but
there's also another host on the Internet that has the same IP -
what happens now? So this is why you cannot use these and other
forms of reserved IPs on the Internet.
EXTRA:
Distinguishing different groups:
You have to compare the first byte on the left in the
address as follows:
Type | First byte | MSB
| in decimal |
----------------------------
A | 1-127 | 0
----------------------------
B | 128-191 | 10
----------------------------
C | 192-223 | 110
----------------------------
D | 224-239 | 1110
----------------------------
E | 240-254 | 1111
----------------------------
NOTES: Yes, we know, we've left A LOT of things unexplained
in this text. With time, we will write more tutorials to cover these
and other subjects. So in the meantime, I suggest that you go to
http://blacksun.box.sk, find the tutorials page and see if there's
anything else that's interesting to you. And remember - we also have
a message board, so if you have any questions, feel free to post
them there.
weird shit (newbie note):
1) Multicast:
(copied from RFC 1112) IP multicasting is the transmission
of an IP datagram to a "host group", a set of zero or more hosts
identified by a single IP destination address. A multicast datagram
is delivered to all members of its destination host group with the
same "best-efforts" reliability as regular unicast IP datagrams,
i.e., the datagram is not guaranteed to arrive intact at all members
of the destination group or in the same order relative to other
datagrams.
The membership of a host group is dynamic; that is, hosts
may join and leave groups at any time. There is no restriction on
the location or number of members in a host group. A host may be a
member of more than one group at a time. A host need not be a member
of a group to send datagrams to it. A host group may be permanent or
transient. A permanent group has a well-known, administratively
assigned IP address. It is the address, not the membership of the
group, that is permanent; at any time a permanent group may have any
number of members, even zero. Those IP multicast addresses that are
not reserved for permanent groups are available for dynamic
assignment to transient groups which exist only as long as they have
members.
Internetwork forwarding of IP multicast datagrams(ip
packets)is handled by "multicast routers" which may be co-resident
with, or separate from, internet gateways. A host transmits an IP
multicast datagram as a local network multicast which reaches all
immediately-neighboring members of the destination host group. If
the datagram has an IP time-to-live greater than 1, the multicast
router(s) attached to the local network take responsibility for
forwarding it towards all other networks that have members of the
destination group. On those other member networks that are reachable
within the IP time-to-live, an attached multicast router completes
delivery by transmitting the datagram(ip packet) as a local
multicast.
*if you donot understand the above do not worry, it is
complicated and dry but reread it and read it again get a dictionary
if it helps. Hacking is not easy.
2) MSB: Most
Significent Bit:
In set numbers the first number on the left is the most
important because it holds the highest value as opposed to the LSB=>
least significent bit, it always holds the the smallest value.
Further information can be acquired from the number systems tutorial
at http://blacksun.box.sk
Credits:
21/04-2000.
Re-edited 6/21/01.
Published on Blacksun Research Facility {BSRF} -
Written by WATER, edited by snider, and
corrections made by Rek.
|