lab 06 ip-addressing

8/13/2019 Lab 06 IP-Addressing

1/19

1

IP Addressing

andSubnettingH ig hP erf orm an ceS wit ch in gan d R ou tin gTel ecom Center W ork shop: Sept4 ,1997 .


2/19

2

Topic

IP Addressing

Subnetting


3/19

3

IP Addresses

Application dataTCP HeaderEthernet Header Ethernet Trailer

Ethernet frame

IP Header

version

(4 bits)

header

length

Type of Service/TOS

(8 bits)

Total Length (in bytes)

(16 bits)

Identification (16 bits)flags

(3 bits)Fragment Offset (13 bits)

Source IP address (32 bits)

Destination IP address (32 bits)

TTL Time-to-Live

(8 bits)

Protocol

(8 bits) Header Checksum (16 bits)

32 bits


4/19

4

IP Addresses

Application dataTCP HeaderEthernet Header Ethernet Trailer

Ethernet frame

IP Header

0x4 0x5 0x00 4410

9d08 0102

00000000000002

128.143.137.144

128.143.71.21

12810 0x06 8bff

32 bits


5/19

5

Hosts, Networks, and Routers

Network A

Network B

Network CRouter

Host 1

Host 2

Host 7

Host 1

Host 12Host 2

Unique IP Address =

Network Number + Host Number


6/19

6

The Most Common Routing

Protocols

Routing protocols exchange network

reachability information between routers.

IP (and ICMP)

TCP UDP

BGP RIP

OSPF EIGRPIS-IS

Cisco proprietary


7/19

7

Classful Addresses

0nnnnnnn

10nnnnnn nnnnnnnn

nnnnnnnn nnnnnnnn110nnnnn

hhhhhhhh hhhhhhhh hhhhhhhh

hhhhhhhh hhhhhhhh

hhhhhhhh

n= network address bit h= host identifier bit

Class A

Class C

Class B


8/19

8

The Classful Address Space

Class Networks Hosts Share of IP

address space

A 127 16,777,214 1/2

B 16,384 65,534 1/4

C 2,097,152 254 1/8

Leads to very inefficient allocation of addresses


9/19

9

Subnets The idea is to share the same IP network

number among multiple subnets

Subnets of a network should reside in the same

general locale (e.g., college campus, corporatelocation, )

Routers on an IP network know their local

subnets

Remote routers need to know only the network

address


10/19

10

Subnetting

Subnetting

Problem: Organizationshave multiple networks

which are independently

managed Solution 1:Allocate a

separate network address

for each network

Difficult to manage

From the outside of the

organization, each networkmust be addressable.

Solution 2:Add another

level of hierarchy to the IP

addressing structure

University Network

Medical

School

Library

Engineering

School


11/19

11

Each part of the organization is allocated a range of IPaddresses (subnets or subnetworks)

Addresses in each subnet can be administered locally

Address assignment with subnetting

University Network

Medical

School

Library

Engineering

School

128.143.0.0/16

128.143.71.0/24

128.143.136.0/24

128.143.56.0/24

128.143.121.0/24


12/19

12

Basic Idea of Subnetting Split the host number portion of an IP address into a subnetnumberand a (smaller) host number.

Result is a 3-layer hierarchy

Then: Subnets can be freely assigned within the organization Internally, subnets are treated as separate networks

Subnet structure is not visible outside the organization

network prefix host number

subnet numbernetwork prefix host number

extended network prefix


13/19

13

Routers and hosts use an extended network prefix(subnetmask)to identify the start of the host numbers

Subnetmask

128.143 137.144

network prefix host number

128.143 144

network prefix host number subnet

number

137

extended network prefix

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0

subnetmask


14/19

14

Advantages of Subnetting

With subnetting, IP addresses use a 3-layer hierarchy:

Network

Subnet

Host

Reduces router complexity. Since external routers do not

know about subnetting, the complexity of routing tables

at external routers is reduced.

Note: Length of the subnet mask need not be identical at

all subnetworks.


15/19

15

No Subnetting

All hosts think that the other hosts are on

the same network

128.143.70.0/16

128.143.137.32/16

subnetmask: 255.255.0.0

128.143.71.21/16


128.143.137.144/16


128.143.71.201/16



16/19

16

128.143.0.0/16

128.143.137.32/24


128.143.71.21/24


128.143.137.144/24


128.143.71.201/24


128.143.137.0/24

Subnet

128.143.71.0/24

Subnet

With Subnetting

Hosts with same extended network prefix

belong to the same network


17/19

17

Different subnetmasks lead to different views of

the size of the scope of the network

128.143.0.0/16

128.143.137.32/26

subnetmask: 255.255.255.192

128.143.71.21/24


128.143.137.144/26

subnetmask: 255.255.255.192

128.143.71.201/16


128.143.71.0/24

Subnet128.143.137.128/26

Subnet

128.143.137.0/26

Subnet

With Subnetting


18/19

18

Optimizing the Allocation of IP Addresses

Routing Table for Router B220.78.168.0 255.255.255.0 220.78.168.1

220.78.169.0 255.255.255.0 220.78.168.1

220.78.170.0 255.255.255.0 220.78.168.1

220.78.171.0 255.255.255.0 220.78.168.1

220.78.172.0 255.255.255.0 220.78.168.1

220.78.173.0 255.255.255.0 220.78.168.1

220.78.174.0 255.255.255.0 220.78.168.1220.78.175.0 255.255.255.0 220.78.168.1

Before Supernetting:

Route

r A

220.78.168.0

220.78.169.0

220.78.170.0

220.78.171.0

220.78.172.0

220.78.173.0

220.78.174.0

220.78.175.0

Router B

Routing Table for Router B

220.78.168.0 255.255.255.0 220.78.168.1

Router B220.78.168.0 Router A

After Supernetting:After Subnetting

Router B

220.78.168.0

220.78.168.64

220.78.168.128220.78.168.192

220.78.169.0

220.78.169.64

220.78.169.128

220.78.169.192

Router

A

220.78.170.0

220.78.170.64

Routing Table for Router B

220.78.168.0 255.255.255.0 220.78.168.1


19/19

19

END.

lab 06 ip-addressing

Documents