1. IP Addressing: introduction
IP address: 32-bit identifier for host, router interface
interface: connection between host/router and physical link
router’s typically have multiple interfaces
host typically has one interface
IP addresses associated with each interface =
223 1 1 1
Network Layer

2. 32 bit destination IP address
IP datagram format
ver
length
32 bits
data
(variable length,
typically a TCP
or UDP segment)
16-bit identifier
header
checksum
time to
live
32 bit source IP address
IP protocol version
number
header length
(bytes)
max number
remaining hops
(decremented at
each router)
for
fragmentation/
reassembly
total datagram
length (bytes)
upper layer protocol
to deliver payload to
head.
len
type of
service
“type” of data
flgs
fragment
offset
upper
layer
32 bit destination IP address
Options (if any)
E.g. timestamp,
record route
taken, specify
list of routers
to visit.
Network Layer

3. Class Handouts… (provided in class)
Network Layer

4. Solve… A software company has 100 employees.
What would be the ideal class from which the company would choose its network IP to prevent wastage of IP addresses?
How many bits would be assigned for network part and how many bits would be assigned for host part?
Note a network chosen by a company can not be chosen by any other company.
The company suddenly goes through increase in number of employees from 100 to 2000.
How many network addresses should the company choose and from which class to avoid wastage of IP addresses?
Network Layer

5. What is the solution? Choose one class B Is it efficient?
A company starts out with one class C LAN…
As it requires more than 254 machines, one class C LAN is not sufficient
Choices?
Choose one class B
Is it efficient?
Choose multiple class C
Network Layer

6. What is the impact of this solution?
Advantages
Certainly able to minimize the IP address wastage
Disadvantages
Increased number of distinct local networks inside the same company
Managing is tough
Moving machines across the local networks
Network Layer

7. What can be a potential solution?
Network Layer

8. IP addressing: CIDR CIDR: Classless InterDomain Routing
network portion of address of arbitrary length
address format: a.b.c.d/x, where x is # bits in network portion of address
network
part
host
/23
Network Layer

9. Solve…
Now the company decided to go with the CIDR mechanism for 2000 employees.
What would be the ideal network address to minimize wastage of IP addresses?
How many bits in network part and how many bits in host part are there?
Network Layer

10. DHCP: Dynamic Host Configuration Protocol
Goal: allow host to dynamically obtain its IP address from network server when it joins network
Can renew its lease on address in use
Allows reuse of addresses (only hold address while connected an “on”)
Support for mobile users who want to join network (more shortly)
DHCP overview:
host broadcasts “DHCP discover” msg [optional]
DHCP server responds with “DHCP offer” msg [optional]
host requests IP address: “DHCP request” msg
DHCP server sends address: “DHCP ack” msg
Network Layer

11. DHCP client-server scenario
server B
arriving DHCP
client needs
address in this
network E
Network Layer

12. DHCP client-server scenario
DHCP server:
arriving
client
DHCP discover
src : , 68
dest.: ,67
yiaddr:
transaction ID: 654
DHCP offer
src: , 67
dest: , 68
yiaddrr:
transaction ID: 654
Lifetime: 3600 secs
DHCP request
src: , 68
dest:: , 67
yiaddrr:
transaction ID: 655
Lifetime: 3600 secs
time
DHCP ACK
src: , 67
dest: , 68
yiaddrr:
transaction ID: 655
Lifetime: 3600 secs
Network Layer