Chapter 8: Internet Protocol (IP) Addressing
Chapter Outline
1. On the Test
a. 2.8: Identify IP addresses (IPv4, IPv6) and their default subnet masks.
b. 2.9: Identify the purpose of subnetting and default gateways.
2. IPv4
a. IPv4 uses a 32-bit address space expressed in binary format or decimal
format.
b. Every IP address is composed of two parts: the network number and the
host number.
c. Every IP host address must be unique. Duplicate addresses result in host
devices that cannot communicate.
d. Distribution of addresses is managed by IANA, which distributes
addresses to regional agencies. The regional agency covering the United
States is ARIN.
e. ARIN allocates IP address blocks to the ISPs for distribution to customers.
3. IP Address Structure
a. The 32 bits of an IPv4 address are broken into four 8-bit groups called
octets.
b. Each octet is 1 byte of information.
c. When an address is written in decimal format, the four octets are separated
by a dot. This is known as dotted decimal notation.
d. In each octet, all 8 bits are assigned a binary value that is often expressed
in decimal format. The decimal values, beginning with the most
significant bit, are 128, 64, 32, 16, 8, 4, 2, and 1, respectively.
e. In binary format, bits are turned on or off to build the unique address for a
node. Bits have a value of either 1 (on) or 0 (off).
f. Conversion of binary to decimal or decimal to binary format can be done
manually or through the use of the Windows calculator in scientific mode.
4. IP Address Classes
a. IPv4 addresses belong to one of five classes of addresses.
b. Class A addresses use the first octet (or 8 bits) to express the network
number, leaving the last three octets (or 24 bits) for host numbers. This
allows 126 networks with 16,777,214 hosts on each network. The opening
bit value is 0.
c. Class B addresses use the first two octets (or 16 bits) for the network
number, and the last two octets (or 16 bits) for the host number. This gives
us 16,384 network numbers with 65,534 hosts on each network. The
opening bit values are 10.
d. Class C addresses use the first three octets (or 24 bits) to indicate the
network number, and the last octet (or 8 bits) for host numbers. There are
e.
f.
g.
h.
2,097,152 network numbers available, with 254 hosts on each of those
networks. The opening bit value for Class C addresses is 110.
Class D addresses are used for multicast transmission and are not
manageable by the public. The opening bit value for a Class D address is
1110.
Class E addresses are used for experimental purposes. The opening bit
value for a Class E address is 1111.
Two addresses from every network range of addresses are reserved for
special usage. One is the network number, and the other is used for
broadcast purposes.
Classful addressing uses the default values in each class for all IP
addressing.
5. Private Addresses
a. Some addresses have been set aside to use on private networks. Those
address spaces are
i. 10.0.0.0-10.255.255.255
ii. 172.16.31.0-172.31.255.255
iii. 192.168.0.0-192.168.255.255.
b. Private addresses are not routed publicly. Therefore, if a router gets a
packet with a private destination address in the header, the packet will not
be routed and will be silently discarded.
c. Automatic Private IP Addressing (APIPA) provides a means for a DHCP
client to self-configure when it cannot reach a DHCP server. APIPA uses
the address space 169.254.0.X.
6. The Loopback Address
a. Another special address encompasses an entire network number. 127.0.0.0
is set aside for the loopback test. The loopback test sends a packet through
the IP stack on the local host. If a response is received, the stack is
installed and functioning.
b. To assign addresses to host devices, the network administrator may
configure every device manually, or the administrator may choose to use
DHCP to allocate addresses to host devices.
7. IP Address Subnet Masks
a. A subnet mask identifies the bits that make up the network number of an
IP address.
b. The mask number is built by turning on (setting to 1) all bits used for the
network number.
c. The default subnet masks for the three consumer classes of addresses are:
i. Class A – 255.0.0.0
ii. Class B – 255.255.0.0
iii. Class C – 255.255.255.0
d. Another way to write the mask for an IP address is by using “slash
notation.” Calculate the number of bits in the mask and follow the IP
address with a slash and the number of bits: 202.16.22.45 /24.
e. The subnet mask also tells the local machine what to do with an outgoing
packet. The destination address is compared to the source address, the two
network numbers are compared, and the decision is made based on the
result of the comparison. If the network numbers are the same, the packet
is going to a host on the local subnet, and an ARP request is sent. If the
network numbers are different, the packet is going to a remote network,
and it will be forwarded to the default gateway (router interface) for
processing.
f. ANDING is the process by which the network number is resolved from an
IP address by ANDING the mask against the host address.
8. IP Address Subnetting
a. Subnetting is the process whereby a classful network address may be
broken down into several smaller subnetworks.
b. Subnetted addresses add an additional level to the address space in the
form of the subnet number.
c. When designing a network that will include subnets, it is important to take
into consideration the current needs of the network and host addresses, as
well as the future needs of the network and host addresses.
d. There are five steps to subnetting:
i.
Determine the number of subnets needed and the maximum
number of hosts on each subnet.
ii.
Determine the number of bits to “steal” from the host bit portion of
the IP address. Use the formula 2N – 2 = the maximum number of
subnets available, where N = the number of bits to “steal”.
iii.
Build a new custom subnet mask to reflect the number of bits taken
from the host section of the address and moved to the network
section of the address.
iv.
Build the new network numbers.
v.
Build the range of IP host addresses for each new subnet by
combining the new network numbers with the identified range of
host bits.
9. IP version 6 (IPv6): IPv6 is the newest version of the Internet Protocol. There are
three key areas that make IPv6 the solution for the future:
a. A much larger address space using 128 bits as opposed to 32 bits in IPv4
b. Built-in support for secure transmission through the inclusion of IPSec in
the protocol stack
c. Support for mobile devices, allowing users to move readily and rely on
their devices to function without reconfiguration
10. IPv6 Address Structure
a. IPv6 addresses are expressed as eight 16-bit fields written in hexadecimal
notation.
b. The address space is divided into a network number and host number and
may include a subnet identifier as well.
c. The host portion of the IPv6 address is always a fixed 64 bits in length.
d. The host portion is usually derived from the MAC address of the device
with filler bits in the center. This is known as the EUI64 address.
e. Addresses may be abbreviated when there are a series of zeros in
contiguous fields of the address. The abbreviator is a double colon (::), but
this may occur only one time in the address. Leading zeros may be
dropped.
f. Three types of IPv6 addresses are used:
i.
Globally unique addresses are the common addresses of devices.
They use the MAC address and the current network number to
form the address. These addresses can be seen locally and globally
(outside the subnet).
ii.
Devices use the link-local address to identify themselves on the
local subnet. These addresses are not visible outside the local
subnet.
iii.
Site-local addresses are used within a site and always read fec0::
/10. They are similar to the private addresses of IPv4.