CH4 Network Layer - Pennsylvania State...

1

Chapter 4:Network Layer

Abdullah KonakSchool of Information Sciences and TechnologyPenn State Berks

A. KonakIST 220/Ch4: Network Layer 2

Learning ObjectivesDescribe Internet addressingUnderstand the functions of the network layer (IP)Understand Domain Name System and name resolution processUnderstand the concept of quality of service

2


Network Layer

Client Application:Web browser

Server Application:Web Server

Network Layer

Host-to-Host Delivery

The transport layer provides and

manages host-to-host delivery over arbitrary

networks.

The transport layer provides and

manages host-to-host delivery over arbitrary

networks.


Duties

The network layer provides host-to-host delivery over same or different types of networks. This services are provided by the Internet Protocol (IP).Functions:

InternetworkingAddressingRoutingPacketizingFragmentingQuality of Service

3


internetwork

The term internetwork refers to an arbitrary collection of networks interconnected to provide host-to-host packet delivery service.

Network 1, Ethernet IEEE 802

Host A Host B Workstation

Network 4FDDI Ring

Host E

Host F

Router 1

Router 2

Network 2, Ethernet IEEE 802

Host C Host D

Router 3Network 3

T1 Dedicated line(point-to-point)


Router• Provides connections between networks (same or different

type) and routing and delivery of data between hosts from different networks.

Network Layer (IP)

Data Link(FDDI)

Physical(FDDI)

Data Link(Ethernet)

Physical(Ethernet)

Host C

FDDIRing

Host A

Host C

RouterEthernetInterface

1Interface

2

Host D

FDDI Frame Ethernet Frame

Physical connection

Connection inside the router

Optical Fiber Cable Twisted Pair Cable

4


Addressing

We need to uniquely identify each device on the Internet. We need an addressing system that can be universally understood by each device on the Internet.


IP Address

Every host on a TCP/IP network must have a unique IP address, which is a 32-bit number (4-octet) that identifies both the host and the network on which the host is located.

IP addresses are expressed in dotted-decimal format, such as

1st Octet 2nd Octet 3rd Octet 4th Octet

11000000 11100100 00010001 0011100114243 14243 14243 14243

{ { { {1st Octet 2nd Octet 3rd Octet 4th Octet

192 . 220 . 170 . 101

5


Examples

Write the dotted decimal notation for

Calculate the maximum and minimum possible decimal numbers for an octet of the IP address? Calculate the maximum number of devices that can be connected to the Internet using a unique IP address?

1st Octet 2nd Octet 3rd Octet 4th Octet

11000000 11100100 00010001 0011100114243 14243 14243 14243


Subnet Masks

IP identifies both the host and the networkon which the host is located.Subnet Mask (SM) is a 32-bit number which identifies which part of the IP is the network address and which part is the host address.

Network Address Host Address

Network Address Host A

10000001 . 10100001 .01000100 . 01010000 IPAddress Binary

129 . 161 . 68 . 80

1444424444314444244443

144424443ddress

IP Decimal

11111111 . 11111111 . 00000000 . 00000000 Subnet Mask Binary 255 . 255 . 0 . 0 Subnet Mask Decimal

14444244443

1 bits identify networks 0 bits identify host

6


Examples

Identify the network and host addresses in the following examples.

1. IP=128.168.1.90 and SM=255.255.0.02. IP=192.168.1.90 and SM=255.255.255.03. IP=192.168.1.90 and SM=255.255.0.2554. IP= 30.0.0.1 and SM=255.0.0.0


Network and Host IDIn TCP/IP networks, two host can directly communicate if they share the same network (subnetwork) IP. IP=181.74.*.* with Subnet Mask=255.255.0.0

RouterRouter

The Router’s Internal Address(The Gateway Address for the site)

The Router’s Internal Address(The Gateway Address for the site)

40.23.20.30Routers External AddressRouters External Address

7


IP Address Classes

255.255.255.0255.255.0.0255.0.0.0Default Subnet Mask25465,53416,777,214Number of Hosts2,097,15216,384126Number of Networks81624Host ID Bits24168Network ID Bits192-223128-1911 -127First Octet Values110100First Bits

Class CClass BClass A

0

1 0

01 1


Example: Class C

IP=192.168.1.* and Subnet Mask=255.255.255.0192.168.1.0 Network IP (NOT a valid host IP)192.168.1.1 1st host IP192.168.1.2 2nd host IP192.168.1.3 3rd host IP. . .. . .192.168.1.254 254th host IP192.168.1.255 Broadcast IP (NOT a valid host IP)

Valid Host IPs

8


Example: Class BIP=165.168.*.* and Subnet Mask=255.255.0.0

165.168.0.0 Network IP (NOT a valid host IP)165.168.0.1 1st host IP165.168.0.2 2nd host IP165.168.0.3 3rd host IP: : :165.168.0.255 255th host IP165.168.1.0 256th host IP

: : :165.168.255.254 65,534th host IP165.168.255.255 Broadcast IP (NOT a valid host IP)

Valid Host IPs


Example: Class AIP=30.*.*.* and Subnet Mask=255.0.0.0

30.0.0.0 Network IP (NOT a valid host IP)30.0.0.1 1st host IP30.0.0.2 2nd host IP30.0.0.3 3rd host IP: : :30.0.0.255 255th host IP30.0.1.0 256th host IP

: : :30.255.255.254 16,777,214th host IP30.255.255.255 Broadcast IP (NOT a valid host IP)

Valid Host IPs

9


Network, Subnet, and Host IDClass B IP=181.74.*.* with Class C Subnet Mask=255.255.255.0


Private IP Addresses

Workstations protected by firewalls and computers that do not connect to the Internet can use unregistered, private IP addresses.When building a private network, you should use one of the special ranges of private IP addresses, rather than assigning IP addresses randomly.

192.168.0.0 through 192.168.255.255

C

172.16.0.0 through 172.31.255.255

B

10.0.0.0 through 10.255.255.255

A

Network AddressesClass

10


NAT (network address translation )

In NAT, the source and/or destination addresses of IP packets are rewritten as they pass through a router.

192.168.0.2

192.168.0.3

192.168.0.4

192.168.0.5

Internet

192.168.0.2192.168.0.3

68.72.1.168.72.1.2

RegisteredPublic IP

PrivateInternal IP

192.168.0.1 68.72.1.3

Router(Firewall)

192.168.0.2 68.72.1.1

68.72.1.2192.168.0.3

192.168.0.4 68.72.1.3

68.72.1.3192.168.0.5

Source IPInside

Source IPOutside

192.168.0.2 68.72.1.1

68.72.1.2192.168.0.3

Destination IPInside

Destination IPOutside

192.168.0.4

192.168.0.5

Hosts 4 and 5 are notdirectly accessible fromoutside


Network Address Port Translation (used by broadband home routers)

192.168.0.2

192.168.0.3

192.168.0.4

192.168.0.5

Internet

192.168.0.2192.168.0.3

8020-21

Port PrivateInternal IP

192.168.0.1 68.72.1.3

Router(Firewall)

192.168.0.2 68.72.1.3

68.72.1.3192.168.0.3

192.168.0.4 68.72.1.3

68.72.1.3192.168.0.5

Source IPInside

Source IPOutside

192.168.0.2 68.72.1.3:80

68.72.1.3:21192.168.0.3

Destination IPInside

Destination IPOutside: Port Number

192.168.0.4

192.168.0.5

Hosts 4 and 5 are notdirectly accessible fromoutside

11


DMZ Host at Home Networks

192.168.0.2

192.168.0.3

192.168.0.4

192.168.0.5

Internet192.168.0.1 68.72.1.3

Router(Firewall)

68.72.1.3

DMZ Host A DMZ host behaves as if itis directly connected to theInternet.


General Guidelines for IP Address Assignments

The first octet of the network ID cannot be 127, 127.0.0.1 is the loopback address in IP. Given an IP and Subnet Mask

The first IP identifies network.The last IP is reserved for broadcast messages.

The host ID of each computer must be unique in a local area network.A registered network ID is required for connecting to the Internet.Each host requires a subnet mask.

12


Domain Name System (DNS) and Address Resolution

Dotted decimal notation IP is not convenient for users, who can more easily remember names than numerical addresses.DNS is a name-to-address directory service that performs name-to-address resolution.

DNS Server

www.psu.edu

DNSDatabase 146.186.157.6

domain name

ip addressUser


Number of Host Computers

13


Hierarchical Structure of DNS


The DNS Database

The DNS database is divided into thousands of contiguous and separately managed zones, which are managed by separate administrators.

14


Name Resolution Process

target: www.microsoft.com

psu.edu

Name resolution is the process of resolving domain names to IP addresses.


Name Servers

A DNS name server stores the zone database file.A DNS name server has the final authority for its zone. A zone can have multiple name servers associated with it.Domain names and their corresponding IPsare also cached in local computers

type "ipconfig /displaydns" in the command prompt to list the cached domain names.

15


In Microsoft XP


Routing

Routing packets over different networks is the main faction of the network layer and the IP protocol

16


Routing Decisions

Criteria: Delay or ReliabilityTechnique: Next-hop routing or path vector routing.


Routing Tables (Next-hop routing)

192.168.3.0 (S2)Net 192.168.3.0

Router 1 Routing Table

192.168.3.0 (S2)Net 192.168.4.0

192.168.2.0 (S1)Net 192.168.2.0

192.168.1.0 (S0)Net 192.168.1.0

Then forward the packet tonetwork (Interface)

If The Destination Network is

Net 192.168.3.0 (S0)Net 192.168.3.0

Router 2 Routing Table

Net 192.168.4.0 (S1)Net 192.168.4.0

Net 192.168.3.0 (S0) Net 192.168.2.0

Net 192.168.3.0 (S0)Net 192.168.1.0

Then forward the packet tonetwork (Interface)

If The Destination Network is

Network192.168.1.0

Network192.168.2.0

interface S0

interface S1

interfaceS2 192.168.4.0interface

S1Network

192.168.3.0interface

S0 Router 2Router 1

17


Routing Tables

Routing tables for the Internet are usually Routing tables for the Internet are usually networknetwork--specific rather than hostspecific rather than host--specific. specific. The router routes the packet to the final The router routes the packet to the final network; it is then broadcast to reach the final network; it is then broadcast to reach the final destination. destination. NetworkNetwork--based routing reduces the size of based routing reduces the size of routing tables.routing tables.


Static vs Dynamic Routing

Static Routing: Information is entered manually and does not change automatically.Dynamic Routing: Routing tables are created and maintained by router dynamically using a routing protocol.

18


Hierarchical Routing: Autonomous System• Routing in the Internet is hierarchical. Delivery is first

made to the autonomous system, then to the network, and finally to the host. Hierarchical routing reduces the size of the routing tables.

A

BC

D

E

F

G

I

J

K

KL

M

N

O

P

R

Exterior Router

Interior Router

Router XS1

S2


Routing Protocols

Routers in the Internet inform each other and update their tables using routing protocols such asRouting Information Protocol (RIP)

A router shares its routing table with its neighbors by sending the routing table to them at fixed intervals.

Open Shortest Path First (OSPF)Border Gateway Protocol (BGP)

19


Routing Information Protocol (RIP)

NetworkA

NetworkB

S0 S2

S1 NetworkDS1

NetworkC S0

S0 NetworkES1

Router 4

NetworkF

S1

S0

Destination Interface HopsRouter 1

A S0 0C S1 0


B S2 0C S0 0D S1 0


D S0 0E S1 0


E S0 0F S1 0

Router 3Router 2Router 1


RIP Exercise:

1. Router 1 sends its table to Router 2. Update the Router 2 Table.

2. Router 2 sends its table (updated) to Router 3. Update the Router 3 Table.




20


Fragmentation


PIv4 Header

Date post:	11-Mar-2020
Category:	Documents
Upload:	others
View:	3 times
Download:	0 times

CH4 Network Layer - Pennsylvania State...

Documents