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 classbased 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 Ranges
Determined 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 onebits 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 208.147.66.0
After 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
Thank you for Attending!
Introduction to TCPIP
References
 Configuring Windows Server 2008 Network Infrastructure by
J.C. Mackin and Tony Northrup
 Microsoft Technet
 Wikipedia.org