CIDR notation
Address class is no longer uniquely identifiable from the address We must find a way of telling routers the size of the
network part of the address Done by including a number along with the network
address
E.g. 73.5.0.0/ 17
• In the above example, the first 17 bits of the address are the network part
• You can search for more example CIDR address blocks at http://www.arin.net
How does a company allocate a large pool of addresses?
5 - 4
Ex. UNCW has 152.20.0.0 / 16 which gives them a possible 65,536 IP addresses (2(32-16))
Possible approach to assigning IP addresses:
As soon as a computer comes online, you can assign them the next IP address available.
Desktop in CIS
Laptop in Union
Workstation in Library
How does a company allocate a large pool of addresses?
5 - 5
Alternative Method:
Each college or building allocated a contiguous set of IP addresses
Desktop in CIS
Laptop in Union
Workstation in Library
CIS152.20.1.0 -152.20.1.255
Fisher Union152.20.2.0 -152.20.2.255
Library152.20.3.0 -152.20.3.255
Subnetting and network structure
Each Ethernet is given a unique subnetwork ID Enables broadcasting within the Ethernet Each computer on the Ethernet must be part of this
network
Subnetting enables the partition of a large address pool into multiple smaller blocks
University campus
Business school subnet131.247.2.0 – 131.247.4.255
Library subnet131.247.1.0 – 131.247.1.255
Engineering subnet131.247.6.0 – 131.247.7.255
Hospital subnet131.247.5.0 – 131.247.5.255
Library Ethernet
Engineering EthernetBusiness School Ethernet
Ho
spita
l Eth
erne
t
Cisco 3600SERIES
0 1
READY
ACTIVE
PCMCIA
1
0
COM AUXSYSTEM RPS
Main campus router
Subnets and IP Addresses
10000011 11110111 00010000 11101011
131 . 247 . 16 . 235
Network ID(USF)
Host ID(worskstation 24 in lab)
Network part of IP address Host part of IP address
What does UNCW’s IP Addresses look like?
3-part interpretation of IP addresses
8
10000011 11110111 00010000 11101011
131 . 247 . 16 . 235
Network ID(USF)
Subnet ID(College of Business)
Host ID(worskstation 24 in
lab)
Network part of IP address
Host part of IP address
Subnet ID component of host part of IP address
Host ID component of host part of IP address
Subnets - How do you decide who gets what address?
5 - 9
Group of computers on the same LAN with IP numbers using the same prefix
Assigned addresses For example:
• Subnet 152.20.234.x– Computers in CIS labs (x is between 0 & 255)
• Subnet 152.20.244.x & 152.20.196.x – Computers in CIS Offices (x is between 0 & 255)
• Subnet 129.79.125.x– Computers in Cameron
Does anyone see a problem with the subnets above?
Subnet: Example
5 - 10
CIS
152.20.244.X172.20.101.X
Cameron
172.20.102.X
Psych
172.20.103.X
Library
172.20.104.XR
R
R
R
R
Address: 152.20.5.56
Address: 152.20.5.70
Address: 152.20.244.254 Address: 172.20.104.254
Campus BackboneAddress: 152.20.5.X
Subnetting example
Consider an organization with a /16 network address block (131.247.0.0/ 16) Most medium-large organizations fall in this category Also, most State Universities
Say, after analysis, the organization settles on 5-bit subnet IDs
Example with 5-bit subnet IDs
Subnet ID Campus unit Subnet ID Campus unit Subnet ID Campus unit
00001 (1) College 1 00010 (2) College 2 00011 (3) College 3
00100 (4) College 4 00101 (5) College 5 00110 (6) College 6
00111 (7) College 7 01000 (8) College 8 01001 (9) College 9
01010 (10) College 10 01011 (11) <future college> 01100 (12) <future college>
01101 (13) Dorm 1 01110 (14) Dorm 2 01111 (15) <future dorm>
10000 (16) <future dorm> 10001 (17) Branch campus 1 10010 (18) Branch campus 2
10011 (19) <future branch campus >
10100 (20) Administration 10101 (21) Campus IT
10110 (22) <future expansion>
10111 (23) <future expansion>
11000 (24) <future expansion>
11001 (25) <future expansion>
11010 (26) <future expansion>
11011 (27) <future expansion>
11100 (28) <future expansion>
11101 (29) <future expansion>
11110 (30) <future expansion>
Network ID + subnet ID for colleges in example
Campus unit Subnet ID First 2 parts of IP addresses by college
College 1 00001 10000011.11110111.00001_ _ _ . _ _ _ _ _ _ _ _
College 2 00010 10000011.11110111.00010 _ _ _ . _ _ _ _ _ _ _ _
College 3 00011 10000011.11110111.00011 _ _ _ . _ _ _ _ _ _ _ _
College 4 00100 10000011.11110111.00100 _ _ _ . _ _ _ _ _ _ _ _
College 5 00101 10000011.11110111.00101 _ _ _ . _ _ _ _ _ _ _ _
College 6 00110 10000011.11110111.00110 _ _ _ . _ _ _ _ _ _ _ _
College 7 00111 10000011.11110111.00111 _ _ _ . _ _ _ _ _ _ _ _
College 8 01000 10000011.11110111.01000 _ _ _ . _ _ _ _ _ _ _ _
College 9 01001 10000011.11110111.01001 _ _ _ . _ _ _ _ _ _ _ _
College 10 01010 10000011.11110111.01010 _ _ _ . _ _ _ _ _ _ _ _
Complete subnet addresses for colleges in example
Campus unit Subnet address (binary) Subnet address (decimal)
College 1 10000011.11110111.00001000.00000000 131.247.8.0/ 21
College 2 10000011.11110111.00010000.00000000 131.247.16.0/ 21
College 3 10000011.11110111.00011000.00000000 131.247.24.0/ 21
College 4 10000011.11110111.00100000.00000000 131.247.32.0/ 21
College 5 10000011.11110111.00101000.00000000 131.247.40.0/ 21
College 6 10000011.11110111.00110000.00000000 131.247.48.0/ 21
College 7 10000011.11110111.00111000.00000000 131.247.56.0/ 21
College 8 10000011.11110111.01000000.00000000 131.247.64.0/ 21
College 9 10000011.11110111.01001000.00000000 131.247.72.0/ 21
College 10 10000011.11110111.01010000.00000000 131.247.80.0/ 21
Subnet Masks
Used to make it easier to separate the subnet part of the address from the host part.
Example Subnet: 149.61.10.x Subnet mask: 255.255.255.000 or in binary
11111111.11111111.11111111.00000000
Example Subnets: 149.61.10.1-128, Subnet mask 255.255.255.128 or, in binary:
11111111.11111111.11111111.10000000
5 - 18
Subnet mask operation
What does a subnet mask do? The 0’s in the subnet mask block (mask) the
corresponding bits in any destination address
The 1’s in the subnet mask allow the corresponding bits to be seen
The Result is the subnet address
How a network is setup for IP addresses
Within the address range of each IPv4 network, we have three types of addresses:
• Network address - The address by which we refer to the network
• Broadcast address - A special address used to send data to all hosts in the network
• Host addresses - The addresses assigned to the end devices in the network
5 - 24
Case study – networks in the retail sector
Both Wal-Mart and K-Mart started in 1962
K-Mart grew rapidly at first 250 stores in 1967, compared to 18 Wal-Marts Each K-Mart store had 6 times the revenue of a Wal-Mart
store
2002 K-Mart filed for bankruptcy For the first time, Wal-Mart was the largest company in
America by revenue
Top Related