Specifications

27
We will refer to the first block as "24-bit block", the second as
"20-bit block", and to the third as "16-bit" block. Note that (in
pre-CIDR notation) the first block is nothing but a single class
A network number, while the second block is a set of 16
contiguous class B network numbers, and third block is a set of
256 contiguous class C network numbers.
An enterprise that decides to use IP addresses out of the address
space defined in this document can do so without any coordination
with IANA or an Internet registry. The address space can thus be
used by many enterprises. Addresses within this private address
space will only be unique within the enterprise, or the set of
enterprises which choose to cooperate over this space so they may
communicate with each other in their own private internet.
In our implementation DHCP is built into the Multitech broadband router. We use Class C private
addresses in the range of 192.168.2.x this allows up to 254 hosts on the LAN. The IP address of the NAT
router is statically assigned as 192.168.2.1. The DHCP server in the router then assigns an IP address to
each client from the pool of remaining addresses.
Some devices work better with a static address. Our local web and print server are assigned pseudostatic
addresses so the address never changes. An option in the router forces the router to always issue the same
address based on its Ethernet MAC address.
7.4.5 AutoIP
The addressing techniques discussed so far require manual entry of an address or that a DHCP server exist
on the network. In most situations this works well. But what happens in a simple environment when one
just wants to connect a couple of PC and not implement any network infrastructure. AutoIP was developed
to solve this problem. If the host is configured to obtain a dynamic address and a DHCP server cannot be
found the host assigns an address to itself from another pool of reserved addresses.
When this happens the machines picks a random address from the AutoIP address pool, and tests to see if
any device on the LAN is already using it, if not it assigns itself the address. If the address is in use it picks
another one and tries again.
AutoIP address block:
169.254.0.0 - 169.254.255.255 (169.254/16 prefix)
Refer to IPv4 Link Local spec for more information about AutoIP.
7.4.6 LocalHost Address
127.0.0.1 is a reserved loopback address. This is useful for testing to makes sure everything in the computer
is working correctly. This allows you to sent packet to the machine you are running on.
7.4.7 Address Resolution Protocol (ARP)
IP addresses represent the global numbering scheme of the Internet. The addressing scheme used by the
physical network is different. For example Ethernet uses a 48-bit MAC address. ARP provides the
mechanism to determine the IP address if the MAC address is known and vice versa.