osi network layer

© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1

OSI Network Layer

Network Fundamentals – Chapter 5

ITE PC v4.0Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Network Layer Protocols and Internet Protocol (IP)

Define the basic role of the Network Layer in data networks

Define services & applications

Define hosts



Identify the basic characteristics and the role of the IPv4 protocol

Attributes (characteristics) of IP


Network Layer Protocols and Internet Protocol (IP) Describe the implications for the use of the IP protocol as it is

connectionless

Packets are sent before contacting destination


Network Layer Protocols and Internet Protocol (IP) Describe the implications for the use of the IP protocol as it is

considered an unreliable protocol


Network Layer Protocols and Internet Protocol (IP) Describe the implications for the use of the IP as it is media

independent


Network Layer Protocols and Internet Protocol (IP) Describe the role of framing in the Transport Layer and explain

that segments are encapsulated as packets



Identify the major header fields in the IPv4 protocol and describe each field's role in transporting packets

TTL is used to prevent endless loop.


Grouping Devices into Networks and Hierarchical Addressing List several different reasons for grouping devices into sub-

networks and define several terms used to identify the sub-networks (managements, performance, security, control)


Grouping Devices into Networks and Hierarchical Addressing List several ways in which dividing a large network can increase

network performance


Grouping Devices into Networks and Hierarchical Addressing List several ways in which dividing a large network can increase

network security


Grouping Devices into Networks and Hierarchical Addressing Explain the communication problems that emerge when very large

numbers of devices are included in one large network


Grouping Devices into Networks and Hierarchical Addressing

Describe how hierarchical addressing solves the problem of devices communicating across networks of networks


Cl. w N. ID H. ID No. Net No. Host

A 1-126 w x.y.z 126 2563-2=16777214

B 128-191 w.x y.z 64*256=16384 2562 -2= 65534

C 192-223 w.x.y z 32*2562 = 2097152 256-2 = 254

Class Mask High bits IP ranges

A 255.0.0.0 0 1.0.0.1 – 126.255.255.254

B 255.255.0.0 10 128.0.0.1 – 191.255.255.254

C 255.255.255.0 110 192.0.0.1 – 223.255.255.254

Classes of IP Address

The Two unused addresses are :

• This Net (Zeros for Host ID)

• Broad Cast (255 for Host ID)


• Loopback Address : 127.x.y.z for testing internal configuration. Packets send to loopback address are not put out onto the wire, they are processed locally & treated as incoming packets.

• Broadcast Address : assigning 255 to host ID (sending packets

• to all hosts in the Net).

192.34.200.255 all hosts of 192.34.200.0 network

130.50.255.255 all hosts of 130.50.0.0 network

• This network : assigning 0 to host ID.

192.34.200.0 ; 130.50.0.0

• Special Case Source Addresses

all internet addresses 0.0.0.0

In DHCP net, IP address of each host is initially 0.0.0.0

Reserved IP Addresses


Class Invisible Ranges (non routed addresses) abbreviated

A 10.0.0.1 – 10.255.255.254 16000000 10.0.0.0 / 8

B 172.16.0.1 – 172.31.255.254 10000000 172.16.0.0 / 12

C 192.168.0.1 – 192.168.255.254 65000 192.168.0.0 / 16

Private IP Addresses

SubnettingAdvantagesBy subnetting, the 2 portions of IP become 3 portions : Net Portion , Subnet portion & Host portion, this can be done by borrowing bits from Host portion.IPv6 vs IPv4 16 Bytes → 3.4 x 10 38 IP Addresses 4 Bytes → 4.3 x 10 9 IP Addresses


ARP vs RARP

Static vs Dynamic IP Addresses

BooTP

Serve to distribute IP Address from a manually created data base (fixed IP for each computer).

DHCPInstalling DHCP service on Server computer (NOS).Configuration this DHCP Server. Configuration each client to obtain its IP from DHCP Server.


Fundamentals of Routes, Next Hop Addresses and Packet Forwarding

Describe the role of an intermediary gateway device in allowing devices to communicate across sub-divided networks

Router used Net ID to forward packets



Trace the steps of an IP packet as it traverses unchanged via routers from sub network to sub-network



Describe the role of a gateway and the use of a simple route table in directing packets toward their ultimate destinations



Define a route and its three key parts



Describe the purpose and use of the destination network in a route

Fa0/0

2

172.16.0.0/12

What will happen if we add the 172.16.0.0/12 to the left of Router A?

A



Describe the purpose and use of the next hop in a route

Incorrect configuration of GW on a host, will cause this host to be unable to communicate with remote networks

2



Trace the steps of several IP packets as they are routed through several gateways from devices on one sub network to devices on other sub networks



Describe the purpose of routing protocols and the need for both static and dynamic routes



Explain how routes are manually configured to build routing table



Explain the role of routing protocols in building the routing table


SummaryRouting Table of Router A

Type Net ID Mask Next Hop metric

C 150.10.0.0 255.255.0.0 150.10.0.2

R 80.0.0.0 255.0.0.0 210.2.2.2 30

C 210.2.2.0 255.255.255.0 210.2.2.2

C 30.0.0.0 255.0.0.0 30.0.0.2

C 192.168.1.0 255.255.255.0 Fa0/0

* 0.0.0.0 0.0.0.0 30.8.8.2

A150.10.0.0

210.2.2.0

80.0.0.0

30..0.0.0

192.168.1.0

Internet


Words indicating Network Layer of IOS Model

Best Efforts

Connectionless

IP Addressing

Logical Addressing

Packets

Identifying Hosts

Routing Table (Routing Protocols)

Determination of Best Path

Layer Protocols

Transport UDP , TCP

Network IP, ARP, RARP, ICMP, Routing Protocols


Encapsulation Steps

Layer Transmitted Data Header

Application Data

Physical Data

Session Data

Transition Segments Port No.

Network Pakets IP Address

Data Link Frame MAC Address

Physical Bits

osi network layer

Documents