Introduction to TCPIP IPV4

Contents What are Network Layers? Understanding IPV4 Addresses What are Subnet Masks? IP Conversion Understanding Routing and Default Gateway What is Subnetting? What is VLSMs?

What are Network Layers? Network layers are conceptual steps in network communication that

are performed by standards-based programs called protocols. A network protocol defines rules and conventions for

communication between network devices. Protocols for computer networking all generally use packet switching techniques to send and receive messages in the form of packets.

Packets are created in an assembly line process called Encapsulation.

Open Systems Interconnection (OSI) model is a standard architecture that would allow computer systems to exchange information even though they were using software and equipment from different vendors.

Encapsulation

OSI Model

OSI Model

OSI Model

Understanding IPV4 Addresses IPV4 addresses are 32 bit in length. Composed of 4 octets of 8 bits a piece. Dotted-decimal notation: 192.168.23.245 Binary notation: 11000000 10101000 00010111 11110101 IPV4 addresses are used to find devices, not just as a

identification system.

Network and Host Id’s

TCPIP Addresses Public IP Addresses Private IP Addresses APIPA

Public IP Addresses Public addresses are assigned by InterNIC and consist of class-

based network IDs or blocks of Classless Inter-Domain Routing based addresses (called CIDR blocks) that are guaranteed to be globally unique to the Internet.

When the public addresses are assigned, routes are programmed into the routers of the Internet so that traffic to the assigned public addresses can reach their locations. Traffic to destination public addresses are reachable on the Internet.

For example, when an organization is assigned a CIDR block in the form of a network ID and subnet mask, that [network ID, subnet mask] pair also exists as a route in the routers of the Internet. IP packets destined to an address within the CIDR block are routed to the proper destination.

Private IP Addresses Private address space - An IP address in the private

address space is never assigned as a public address. IP addresses within the private address space are known as private addresses. Because the public and private address spaces do not overlap, private addresses never duplicate public addresses.

Hosts addressed with private IP addresses can connect to the internet through a server or a router performing NAT (Network Address Translation).

Private IP RangesDetermined by Internet Assigned Numbers Authority (IANA).

APIPA A feature of Microsoft Windows, APIPA is a DHCP failover

mechanism. With APIPA, DHCP clients can obtain IP addresses when DHCP servers are nonfunctional. APIPA exists in all popular versions of Windows except Windows NT. When a DHCP server fails, APIPA allocates addresses in the private range 169.254.0.1 to 169.254.255.254. Clients verify their address is unique on the LAN using Address Resolution Protocol (ARP). When the DHCP server is again able to service requests, clients update their addresses automatically.

In APIPA, all devices use the default network mask 255.255.0.0 and all reside on the same subnet.

TCPIP Addresses Most companies use a combination of both public IP and

private IP addresses

Public IP > Available Servers

Private IP > Client Computers

TCPIP Addresses An address block is the complete group of individual IP addresses that

shares any single network ID. For example, an organization may purchase from an ISP a /24 address block with network ID 206.73.118. The range of addresses associated with this address block would thus be 206.73.118.0 – 206.73.118.255.

An address block will serve a single broadcast domain with a single router or way out of the network.

A default gateway is the address within the same broadcast domain and assigned to that router port/interface.

An address block can serve as a range of addresses for a single subnet. A subnet is a group of hosts within a single broadcast domain that share the

same network ID and the same default gateway address. The size of the address block will be typically referred to by its subnet mask.

Single Subnet Network

What are Subnet Masks?

A subnet mask is used to determine which part of the 32 bit IPV4 Address should be considered the network id.

For example, when we write 192.168.23.245 /24, the /24 represents the subnet mask and indicates that the first 24 of the 32 bits in that IPV4 address should be considered its network id.

The “/” “Slash Notation” is also know as Classless Inter domain Routing (CIDR).

Subnet Mask Notation /8 = 255.0.0.0 (Class A) /16 = 255.255.0.0 (Class B) /24 = 255.255.255.0 (Class C)

The subnet mask identifies the network id.

Subnet Mask Notation Example /8 = 192.168.23.245 /16 = 192.168.23.245 /24 = 192.168.23.245

Subnet Mask Octet Values

An IPV4 Address with a /24 Subnet Mask

An IPV4 Address with a /26 Subnet Mask

Subnet Mask Notations Compared

Subnet Mask Notations Compared

Subnet Mask Octet Values

Potential Values in Binary Octet

Binary-to Decimal Conversion

10000011

128 + 2 + 1 = 131

Decimal-to-Binary Conversion

209

The first octet is therefore written as follows in binary notation: 11010001

Understanding Routing and Default Gateway The calculation of a network ID using the subnet mask essentially

tells the computer how to send a packet towards a destination. When a computer on a network needs to send a packet to a

remote address, the computer compares it’s own network ID to that of the destination network ID specified in the packet.

If the 2 network IDs match the message is determined to be local and is broadcast to the local subnet.

If the 2 network IDs do not match, the computer sends the packet to an address known as the default gateway.

The router found at this default gateway address then forwards the IPV4 datagram (Packet) in a manner determined by its routing table.

Routing Ip packet over an internetwork

Determining the Number of Addresses Per Address Block If your company purchases a block of addresses from an ISP,

the size of that address block will typically be referred to by its subnet mask. To understand this terminology, then, you need to know how to translate the value of a subnet mask into a specific number of addresses.

To determine the number of addresses in any block, you can start with a single point of memorization: A /24 network (subnet mask 255.255.255.0) always contains 256 addresses.

From this point you can determine the number of addresses in a network simply by halving or doubling 256 as the string of one-bits in the subnet mask is moved to the right or to the left of /24.

Determining the Number of Addresses Per Address Block

For example, if a /24 network (subnet mask 255.255.255.0) has 256 addresses, a /25 network (subnet mask 255.255.255.128) must have 128 Addresses (half of 256), a /26 network (subnet mask 255.255.255.192) must have 64 addresses (half of /25).

Moving in the other direction, if a /24 network has 256 addresses, a /23 network (subnet mask 255.255.254) must have 512 (double 256), a /22 network (subnet mask 255.255.252) must have 1024 (double /23).

Common Address Block Sizes

Determining Host Capacity per Block The host capacity of an address block is the number of

addresses that can be assigned to computers, routers, and other devices.

In every address block assigned to a single broadcast domain and subnet, exactly two addresses are reserved for special use: the all-zeroes host ID, which is reserved for the entire subnet, and the all-ones host ID, which is reserved for the broadcast address of the subnet.

This means that the host capacity of an undivided address block is always two fewer than the number of addresses in that network.

Determining Host Capacity per Block For example, the network 192.168.10.0 /24 has 256

addresses. The specific address 192.168.10.0 is reserved for the network address, and 192.168.10.255 is reserved for the network broadcast address. This leaves 254 addresses that can be assigned to network hosts.

What is Subnetting? Subnetting refers to the practice of logically subdividing a

network address space by extending the string of 1-bits used in the subnet mask of a network. This extension enables you to create multiple subnets or broadcast domains within the original network address space.

Subnetting is used to accommodate a divided physical topology or to restrict broadcast traffic on a network.

Subnetting includes improved security (by restricting unauthorized traffic behind routers) and simplified administration (by delegating control of subnets to other departments or administrators).

Subnetting in a Divided Physical Topology Example You are designing a campus network with 200 hosts spread

over four buildings – Voter Hall, Twilight Hall, Monroe Hall, and Sunderland Hall.

You want each of these four buildings to include 50 hosts. Your ISP has allocated to you the /24 network 208.147.66.0. You can use the addresses 208.147.66.1 – 208.147.66.254

for your 200 hosts. However, if these hosts are distributed among four physically

separated locations, the distances among might be too great to allow the hosts to communicate with one another by means of a local network broadcast.

Subnetting in a Divided Physical Topology Example By extending the subnet mask from /24 to /26 and borrowing

two bits from the host ID portion of your address space, you can divide the network into four logical subnets.

You can use a router in a central location to connect the four physical networks.

The subnet masks for each location with 64 host addresses would be:

208.147.66.0 /26

208.147.66.64 /26

208.147.66.128 /26

208.147.66.192 /26

Subnetting in a Divided Physical Topology Example

Subnet ID When you subnet your network, you are essentially taking some of

your configurable address space from your host ID and moving it to your Network ID.

This string of bits you use to extend your network ID internally within your organization ( relative to the original address block) is known as the subnet ID.

Example: Your ISP has allocated to you the /24 network 208.147.66.0After extending the subnet mask from /24 to /26 and borrowing two bits

from the host ID portion of your address space, the result is you divided the network into four logical /26 subnets:

Subnet IDs

208.147.66.0 /26

208.147.66.64 /26

208.147.66.128 /26

208.147.66.192 /26

Variable-Length Subnnet Masks (VLSMs)

Variable length subnetting is a technique of allocating subnetted network IDs that use subnet masks of different sizes.

For Example, if your /24 address block needs one subnet of 100 computers, a second subnet of 50 computers, and a third subnet of 20 computers, this arrangement cannot be designed with traditional subnet mask options.

Traditional Options for Subnetting a /24 Address Block

Variable-Length Subnnet Masks (VLSMs) Using Variable-Length Subnet Masks will allow you to

accommodate your specific network needs without having to acquire new address space from your provider.

Using Variable-Length Subnet Masks allows you to use various lengths to accommodate three subnets of 100,50, and 20 hosts, respectively.

This particular network configuration will allow for up to four more subnets to be added later.

Variable-Length Subnnet Masks (VLSMs) When you use VLSMs to divide your network into subnets of

varying sizes, the address block is divided up a specific way. If you have a /24 network, for example, you can use the

VLSMs to divide the network into one /25 network, one /26 network, one /27 network and son on.

Note that whenever you use VLSMs, a specific pattern of subnet IDs composed of 1s and a single 0 must be used. The trailing 0 in each subnet ID prevents the address space in each subnet from overlapping with the address space in other subnets.

/24 Variable-length Subnet IDs Example

Variable-Length Subnnet Masks (VLSMs)

Notice that the seventh and final subnet listed is the same size as the sixth and is distinguished by an all-1s subnet ID instead of by the trailing 0 used with the other subnet IDs.

An alternative to using the maximum seven subnets presented, you could define the all-1s subnet ID to any level in the table to replace all the subnets listed below that subnet.

For example, you could define a subnet ID of 11 to replace subnets 3 through 7.

Q&A

Introduction to TCPIP

Thank you for Attending!

References Configuring Windows Server 2008 Network Infrastructure by

J.C. Mackin and Tony Northrup Microsoft Technet Wikipedia.org