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Addressing the Network - IPV4

Part I

Note for Instructors These presentations are the result of a collaboration among the instructors at St. Clair College in Windsor, Ontario.If anyone finds any errors or omissions, please let me know at: [email protected] of an IPv4 Address Each device on a network must be uniquely identified at the Network layer.For IPv4, a 32 bit source and destination address is contained in each packet.His material and additional information was used as a reference in their creation.Devices use binary logic and work with strings of binary numbers.Thanks must go out to Rick Graziani of Cabrillo College.For us, the decimal equivalent is much easier to use and remember.

Addressing the Network - IPV4

Part I

Note for Instructors
These presentations are the result of a collaboration among the instructors at St. Clair College in Windsor, Ontario.
Thanks must go out to Rick Graziani of Cabrillo College. His material and additional information was used as a reference in their creation.
If anyone finds any errors or omissions, please let me know at:
[email protected].

Anatomy of an IPv4 Address
Each device on a network must be uniquely identified at the Network layer.
For IPv4, a 32 bit source and destination address is contained in each packet.

Devices use binary logic and work with strings of binary numbers. For us, the decimal equivalent is much easier to use and remember.

To identify a path or "route" through a network, the address
must be composed of two parts:
Network portion
Host portion

Network Portion:
Some portion of the high-order bits represents the network address.
At Layer 3, we define a network as a group of hosts that have identical bit patterns in the network address portion of their addresses.

Host Portion:
There are a variable number of bits that are called the host portion of the address.
The number of bits used in this host portion determines the number of hosts that we can have within the network.

Binary to Decimal Conversion
In all number systems, the digits start with 0.
A Base-n number system has n number of digits:
Decimal:
Base-10 has 10 digits
9, 8, 7, 6, 5, 4, 3, 2, 1, 0
Binary:
Base-2 has 2 digits
1, 0
Hexadecimal:
Base-16 has 16 digits
F, E, D, C, B, A, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0

Binary to Decimal Conversion
Positional Notation (Decimal Number System):
Means that a digit represents different values depending on the position it occupies.
The value that a digit represents is that value multiplied by the power of the base according to the position the digit occupies.
Computers react only to electrical impulses.
They work with and store data using electronic switches that are either on (1) or off (0).
They can only understand and use data that is in this two state format.
These 1's and 0's are called binary digits or bits.

Broadcast Address
The destination address of a single packet used to communicate to all hosts in a network (Highest Address)
Cannot be assigned to a device.
Each host bit in this address will be 1.

Host Address
The unique address assigned to each device on the network.
Assign any address between the network address (192.168.10.0) and the broadcast address (192.168.10.255).
Addresses 192.168.10.1 through 192.168.10.254.

Types of Communication in an IPv4 Network
In all three types, the address of the originating host is used as the source address in the packet.

Unicast Communications
The process of sending a packet from one host to an individual host.

Special Unicast Addresses
Default Route:
Address - 0.0.0.0 Subnet Mask – 0.0.0.0
When configured, it tells the device….
If you don’t know where to send the frame, send it here

Loopback:
Address - 127.0.0.1
Host applications use it to communicate with each other.
Test TCP/IP configuration on a PC – ping 127.0.0.1

Special Unicast Addresses
Test-Net Addresses:
Address Range 192.0.2.0 to 192.0.2.255
Used for teaching and learning purposes.
Appear in documentation and network examples.
Will be accepted by a network device.
Used to provide examples in RFCs and vendor and protocol documentation.
Should not appear on the Internet.
Experimental Address Range:
Address Range 240.0.0.0 to 255.255.255.254
Reserved for future use.
Cannot be used on IPv4 networks.
Used for research and experimentation.

Public and Private Addresses:
Most IPv4 addresses are public addresses.
A public address is one that is designated for use in networks that are accessible on the Internet.
Networks that require limited or no Internet access, use private addresses.
Private addresses are assigned from blocks of private address space set aside for that purpose.
10.0.0.0/8 (10.0.0.0 to 10.255.255.255)
172.16.0.0/12 (172.16.0.0 to 172.31.255.255)
192.168.0.0/16 (192.168.0.0 to 192.168.255.255)

Broadcast Communications
The process of sending a packet from one host to all hosts in the network.
Broadcasts are not forwarded by a router unless specifically
configured to do so.
The bits in the host portion of a broadcast address will be
all 1s.

Multicast Communications
The process of sending a packet from one host to a selected group of hosts.
Multicasting involves the use of a reserved network of
IP Addresses (224.0.0.0).

Each host that is to participate in a multicast session first joins the multicast group controlled by the router.

When the packet from the source arrives at the router,
it is forwarded to all members of the multicast group.
The reserved multicast network or specific multicast addresses will be displayed in the routing table of a device.
The following is from a PC.

Internet Assigned Numbers Authority (IANA)
To have hosts accessible from the Internet, an organization must have a block of public addresses assigned to them.
IANA is a global organization responsible for the assignment of IPv4, IPv6 and Multicast addresses.
Most companies or organizations obtain their IPv4 address blocks from an ISP.
The ISP loans or rents these addresses to the organization.
If we move our Internet connectivity, the new ISP will provide us with addresses from the address blocks that have been provided to them.
Our previous ISP will loan the returned addresses to other customers.
ISPs have their own set of internal data networks to manage Internet connectivity and to provide related services (DNS, e-mail, website).

ISPs are designated by a hierarchy based on their level of connectivity to the Internet backbone.

Planning to Address the Network
Planning and documentation is an important part of IP Address assignment.
Preventing duplication of addresses.
Each host on a network MUST have a unique address.
Providing and controlling access.
Some servers provide services for both internal and external users.
Filters and access control can be done at Layer 3.
Monitoring security and performance.
Examining network traffic and troubleshooting requires a good knowledge of the addressing scheme

Assigning Addresses Within a Network
The IP Addresses for hosts on a common network segment must all have the same network portion.
Desktop Workstations
Laptops
Internal Servers
External Internet Servers
Printers
Routers
Switches
Each of these should be assigned a logical block of addresses within the address range of the network.

Considerations – Private and Public addresses.
Will there be more devices connected to the network than public addresses allocated by the network's ISP?

Will the devices need to be accessed from outside the local network?

If devices that may be assigned private addresses require access to the Internet, is the network capable of providing a Network Address Translation (NAT) service?

Network Prefixes
How do you know the number of bits assigned to the network and the number of bits assigned to the host?
Prefix Mask:
The address is followed by a number that represents the number of bits (prefix length), beginning from the left, that apply to the network.
A slash (/) is used to separate the address and the prefix length.
192.168.10.2/24

Means that the first 24 bits are the network portion.
The last 8 bits are the host portion.

Networks are not always assigned a /24 prefix.
Depending on the number of hosts on the network, the prefix can be different.
Having a different prefix changes the host range and the broadcast address.

Subnet Mask
How do the network devices know how many bits are the network portion and how many bits are the host portion?
Subnet Mask:
A 32 bit value, expressed in dotted decimal notation, that specifies the number of network bits and the number of host bits.
The Prefix Mask and the Subnet Mask are different ways of representing the same information.
Prefix Mask of /24 or a subnet mask of 255.255.255.0
First 24 bits are the network portion.
The remaining 8 bits are the host portion.

There is a direct, one-to-one relationship between the bits of the IP Address and the bits of the subnet mask.
The subnet mask uses 1 and 0 bits to indicate that the corresponding bit of the IP address is either the network (1) or the host (0) portion.

Reasons to Use AND
The source device uses the ANDing process to determine if the packet is to be sent to the default gateway.
A PC will use it to determine the destination network.
If the destination network is the same as the network where the PC resides, the packet is sent directly to that host.
If the destination network is different, the packet is sent to the default gateway.