NT1210 Introduction to Networking

NT1210 Introduction to Networking

Unit 8:

Chapter 8, The Internet Protocol (IP)

1

Objectives

Identify the major needs and stakeholders for computer networks and network applications.

Identify the classifications of networks and how they are applied to various types of enterprises.

Compare and contrast the OSI and TCP/IP models and their applications to actual networks.

Explain the functionality and use of typical network protocols.

2

Objectives

Differentiate among major types of LAN and WAN technologies and specifications and determine how each is used in a data network.

Explain basic security requirements for networks.

Use network tools to monitor protocols and traffic characteristics.

Plan and design an IP network by applying subnetting skills.

Explain the functionality of typical network protocols.

3

Objectives

Plan and design an IP network by applying subnetting skills.

Categorize TCP/IP protocols according to network model layers.

Describe how TCP/IP addressing moves data packets through networks.

4

Introducing the Internet Protocol (IP)

TCP/IP Model review: Layers 1 and 2 Protocols

Figure 8-1Example LAN/WAN Standards and Types in the TCP/IP Model5


TCP/IP Model review: Upper layers define non-physical (logical) networking functions

Figure 8-2Various Perspectives on the TCP/IP Model and Roles6


Network Layer protocols IP: Most important protocol defined by Network layer

Almost every computing device on planet communicates, and most use IP to do so

Network layer also defines other protocols

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Network Layer protocols: Part 1

Table 8-1Other TCP/IP Network Layer Protocols

Name Full Name Comments

ICMPInternetwork Control Message Protocol

Messages that hosts and routers use to manage and control packet forwarding process; used by ping command

ARPAddress Resolution Protocol

Used by LAN hosts to dynamically learn another LAN host’s MAC address

DHCPDynamic Host Configuration Protocol

Used by host to dynamically learn IP address (and other information) it can use

DNSDomain Name System/Service

Allows hosts to use names instead of IP address; needs DNS server to translate name into corresponding IP address (required by IP routing process)

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Network Layer protocols: Part 2

Table 8-1Other TCP/IP Network Layer Protocols

Name Full Name Comments

RIPRouting Information Protocol

Application that runs on routers so that routers dynamically learn IP routing tables (used to route IP packets correctly); open standard protocol defined in RFC 2453

EIGRPEnhanced Interior Gateway Routing Protocol

Proprietary routing protocol owned by Cisco Systems

OSPFOpen Shortest Path First

Open source routing protocol defined in RFC 2328

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IPv6: Next generation of IP addressing.

Needed because IPv4 addresses exhausted.

128-bit long addresses: 2128 or 3.4x1038 or over 340 undecillion IPs, that’s 340 with 36 zero’s after it.

Customer usually gets /64 subnet, which yields 4 billion times IPs available in all of IPv4.

Comparison: Number of IPv4 addresses equal to weight of cat; number of IPv6 addresses equal to weight of Earth and provides enough IP addresses for every grain of sand on every beach on earth.

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Migration to IPv6 has taken over decade and still in process.

IPv6 originally defined back in mid-1990s.

June 6, 2012 – Was the scheduled IPv6 Day, official worldwide “switch over” day, moved up to February 2012.

Figure 8-3IPv4 Vs. IPv6 Timeline11


IP defines many functions that work together with one ultimate goal: To send data from one host to another host through any TCP/IP network.

Most important functions include:

Creating end-to-end physical paths through TCP/IP network by interconnecting physical networks (LANs and WANs) using routers

Identifying individual hosts and groups of hosts using IP addressing

Routing (forwarding) IP packets to correct destination host

Figure 8-4Example of a Post Office Sorting a Letter Sent to Hollywood, California12


IP is like Post Office

Figure 8-4Example of a Post Office Sorting a Letter Sent to Hollywood, California13


Routers in IP network: Interconnect LANs and WANs via physical connectors called interfaces Example: Cisco 1841 router with two built-in Gigabit Ethernet

LAN interfaces that use RJ-45 connectors

Figure 8-5Enterprise Class Router, LAN Interfaces, and WAN Interfaces14


IP interconnects LANs and WANs

Figure 8-7Interconnected LANs and WANs: Redundancy, but No LAN/WAN Detail15


IPv4 Addresses 32 bits Expressed in binary and dotted decimal forms Source and destination IP addresses included in 20-byte IP

header added to all IP packets

Figure 8-8IPv4 Header Format and Fields16


Converting binary IP address to dotted decimal 1. Separate 32 bits into 4 groups of 8 bits each

2. Do binary-to-decimal conversion of each 8-bit number (each decimal value between 0 and 255)

3. Put period (dot) between each decimal number

Figure 8-9Generic View of Converting from Binary IP Address to DDN Format17


Example: Converting binary IP address to dotted decimal

Figure 8-10Converting Binary IP Address to DDN 10.1.2.318

Introducing the Internet Protocol (IP): Routing

Routing IP Packets from Source to Destination

IP addressing groups addresses into networks

All addresses with same value in first parts of addresses considered to be in one network

Example: All addresses that begin with 11, 12, 13, 14, or 15 in that particular network

Figure 8-11Example IP Address Groupings: All with the Same First Octet in the Same Group

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IP routing example with routing tables: PC11 in left LAN sends IP packet to address 12.1.1.21 (LAN on upper right)

Figure 8-12Example IP Address Groupings: All with the Same First Octet in the Same Group

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Routers build routing tables in two ways Static configuration: Routes entered manually and do not

change

Dynamic routing protocol: Application router uses to automatically learn new routes from other routers

Figure 8-13Routing Protocols Advertising All Addresses that Begin with 12 as One Route21

Introducing the Internet Protocol (IP): Other Protocols

Domain Name System/Service (DNS): Mapping names to IP addresses Users use names; IP

routing uses numbers

DNS translates name into corresponding IP address

DNS client sends DNS Request message

DNS server returns DNS Reply

Figure 8-14DNS Name Resolution Request, Reply, and Packet to Server1 IP Address22

Introducing the Internet Protocol (IP): Other Protocols

Figure 8-15IP with its Support Protocols23

Layer 3 - Network

IP Addressing on User LANs: Network Settings

Locations Need IP addresses

Each LAN and WAN interface on hosts and routers need IP address to communicate

Figure 8-17IP Addresses Used on Every LAN/WAN Interface24


IP Address grouping: Allows IP routing to work better

Routers list one number to represent each network (address group) in routing tables

Figure 8-18IP Address Groupings: IP Networks25

IP Addressing on User LANs: Network Settings Original IPv4 RFC defined way to group IPv4 addresses

using IP address classes (classful IP addressing) Every possible IPv4 address falls into class

Table 8-2Summary of IPv4 Address Classes Based on First Octet Values26

First Octet Class Purpose

0 A Reserved

1 - 126 A Unicast addresses, in class A networks

127 A Reserved for loopback testing

128 - 191 B Unicast addresses, in class B networks

192 - 223 C Unicast addresses, in class C networks

224 - 239 D Multicast addresses; not used as unicast IP addresses

240 - 255 E Experimental; not used as unicast IP addresses

IP Addressing on User LANs: Network Settings Class A includes lower half of IPv4 address space: All

IPv4 address that begin with first octet between 0 and 127

Table 8-3Example Class A Networks27

Network ID Class A IP Network ConceptSize (Number of Addresses)

1.0.0.0 All addresses with a first octet equal to 1 > 16,000,000




… Etc…. > 16,000,000


IP Addressing on User LANs: Network Settings Class B includes ¼ of IPv4 address space with first

octet value from 128 – 191 Includes medium number (216) of medium sized IP

networks for approximately 65,000 hosts per network

Table 8-4Example Class B Networks28

Network ID ConceptSize (Number of Addresses)

128.1.0.0 All with a first two octets equal to 128.1 > 65,000






IP Addressing on User LANs: Network Settings Class C includes 1/8th of IPv4 address space with first

octet between 192 and 223 Large number of small IP networks: over 2,000,000 IP

networks, each with 256 IP addresses each

Table 8-5Example Class C Networks29

Network ID ConceptSize (Number of Addresses)

192.1.1.0 All with a first three octets equal to 192.1.1 254







LAN IP address classes summary

Figure 8-20Summary of How Class Rules Break Down the IPv4 Address Space30


Private addresses: Classful IP networks reserved for enterprises to use in their network designs

Can only be used on local LAN; can’t be routed through WAN (non-routable)

Not regulated by agencies such as ARIN or ICANN

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Network ID Concept Size (Number of Addresses)

10.x.x.x Class A Private IP addressing spaceOver 16,000,000 networks of over 16,000,000 IPs each

172.16.x.x –172.31.x.x

Class B Private IP addressing spaceOver 65,000 networks of over >65,000 IPs each

192.168.x.x Class C Private IP addressing spaceOver 65,000 networks of 256 IPs each


Static IP address assignment: Manually configured

Figure 8-21Static IP Address Assignment on Mac OS X32


Most host OS’s allow static configuration of several network settings

Figure 8-22Host IP Settings33


Dynamic Host Configuration Protocol (DHCP) defines way hosts can lease IP address from DHCP network server so does not have to be configured statically Operates on client-server concept

DHCP protocol defined by set of RFCs

Figure 8-23Sample Network for DHCP Discussions34


Example: IP address assignment design using both DHCP and statically assigned addresses

Table 8-6Address Planning: Some Static, Some DHCP, for Every LAN35

Location Type Range

Atlanta LANStatic 11.1.1.1 - 11.1.1.254

DHCP 11.1.2.1 - 11.1.2.254

Boston LANStatic 172.20.1.1 - 172.20.1.254

DHCP 172.20.2.1 - 172.20.2.254

San Fran LANStatic 172.30.1.1 - 172.30.1.254

DHCP 172.30.2.1 - 172.30.2.254


Once DHCP server exists in network and has been configured with set of IP addresses to lease, DHCP clients can request IP addresses

Figure 8-24DHCP Lease Process between a DHCP Client and Server36


User can see results of DHCP process from computer

Figure 8-25DHCP Client Configuration on Mac OS X37


DHCP example: Crossing networks to access DHCP server

Figure 8-26Remote DHCP Client in Boston38

Short Break

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Take 10

IP Routing with Focus on Layer 3

IP defines how to route packets across TCP/IP network

Some routing tasks must use logic from lower two layers because Network layer (3) cannot physically send bits

Network layer relies on Layers 1 and 2 logic for this

Figure 8-27IP Routing Perspective, While Ignoring LAN/WAN Details40


Router must have IP routing table with useful entries to route IP packets.

Routing table may list multiple routes.

Each IP route identifies network, as well as other information about how to send packets to that network.

Routers look at incoming packet’s destination IP address and compare it to list of network IDs in its routing table to determine where to send packet to destination.

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Finding a classful network ID based on IP address

Figure 8-28Five Classful Networks in a Small Corporate Network42


Each route in routing table lists:

Information about how to match IP packets

Forwarding instructions that tell router where to forward packets to (e.g., next router)

Example: R1’s IP routing table shows five network IDs so it knows routes to all five networks

Figure 8-29R1 Routing Table with Routes for Five Classful Networks43


Router compares incoming IP packet’s destination address to information in its routing tables to find best route to destination

Figure 8-30How Router R1 Uses its IP Routing Table: Match and Forward44


Figure 8-31Routing from End-to-End: Multiple Cooperative Routing Decisions45

IP Routing with Focus on Layer 3: Subnetting

Classful IP networks and wasted IP addresses

Subnetting: Process of subdividing network to create smaller groups of consecutive IP addresses

Subnets (subdivided networks): Smaller groups of addresses

Figure 8-32Numbers of Classful Networks, and Their Sizes46


Example: Several subnets created by subnetting network 10.0.0.0

Each subnet has subnet/network ID

Figure 8-33Subdividing (Subnetting) Class A Network 10.0.0.047


Example continued: IP addresses and networks replaced with five subnets of network 10.0.0.0

Figure 8-34Sample Corporate Network Using Subnets of Network 10.0.0.048


Subnet mask: Shows how much of IP address for each device is in common to all IPs in subnet

Example 255.255.255.0 (/24): First three octets (first 24 bits) must be equal for all subnets in network

PC11 sends packet to PC21 (destination IP address 10.1.2.21)

R1 will have route for PC21’s subnet (network ID 10.1.2.0)

Figure 8-35Routing Logic with Subnets and Masks49


Classful networks have default subnet mask based on each class

Class A: 255.0.0.0 (8 bits)

Class B: 255.255.0.0 (16 bits)

Class C: 255.255.255.0 (24 bits)

If subnet mask anything other than default, then subnetting being used

Figure 8-35Routing Logic with Subnets and Masks50


How to calculate subnets1. Determine network class (A, B, or C)

2. Determine EITHER number of hosts needed for each subnet OR how many subnets needed

3. Determine how many bits needed to provide correct number of hosts/subnets; last subnet is NOT usable

4. Calculate IPs for each subnet; first IP identifies subnet (Network ID) and last IP identifies broadcast address

5. Determine subnet mask (total number of bits for network/subnet ID)

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Example: Calculating subnets for network 192.168.12.0 Class: C Number of subnets needed: 14 Number of bits needed to supply 14 subnets: 3 Number of bits left to determine number of IPs per subnet: 5

(results in 32 IPs per subnet) Subnet mask: 255.255.255.224 (default 16 bits + 3 more bits

for subnetting = 19 bits)

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53

Subnet No.

Network ID Host Range IPs Broadcast IP

0 192.16.12.0 192.16.12.1 – 192.16.12.30 192.16.12.311 192.16.12.32 192.16.12.33 – 192.16.12.62 192.16.12.632 192.16.12.64 192.16.12.65 – 192.16.12.94 192.16.12.953 192.16.12.96 192.16.12.97 – 192.16.12.126 192.16.12.1274 192.16.12.128 192.16.12.129 – 192.16.12.158 192.16.12.1595 192.16.12.160 192.16.12.161 – 192.16.12.190 192.16.12.1916 192.16.12.192 192.16.12.161 – 192.16.12.222 192.16.12.2237 192.16.12.224 192.16.12.225 – 192.16.12.254 192.16.12.255


What happens when PC11 sends IP packet to PC12: Same subnet

1. PC11 determines its own IP address and subnet mask (10.1.1.11 and 255.255.255.0)

2. PC11 decides determines destination is in same subnet

3. PC11 sends packet directly to PC12 without going through router R1

Figure 8-36IP Host Routing Logic: Local Destination54


What happens when PC11 sends IP packet to PC12: Different subnets

1. Host’s default gateway (default router) setting tells it where to send packets when they have destination address in different subnet

2. Default gateway tells host IP address of router attached to its LAN

3. Router then consults its routing table and determines how to deliver packet

Figure 8-37IP Host Routing Logic: Remote Destination55

IP Routing with Layer 1, 2, and 3 Interactions

Encapsulation: Action taken by lower layer when it takes data from higher layer and adds header (and sometimes trailer) to higher layer’s data

Example: PC11 opened web browser and tried to connect to URL at web server: PC11 creating bits it uses to send to server S1 (web server)

Figure 8-38Encapsulation Review: Application, Transport, and Network Layers56


PC encapsulating IP packet into Ethernet frame (step 4)

Sending bits over LAN cable into network (step 5)

Figure 8-39Encapsulation Review: Data Link Layer57


De-encapsulation: On the destination side

Figure 8-40De-encapsulation on a Receiving Host (S1)58


Addressing frames and packets when crossing SAME subnet: Both MAC and IP addresses in Ethernet frame and encapsulated IP packet

Figure 8-42IP and Ethernet Addresses, PC11 to server S1, Same Subnet59

IP Routing with Layer 1, 2, and 3 Interactions To learn destination MAC address, sending device uses

Address Resolution Protocol (ARP) and info in ARP table

Table 8-9How a Sending IP Host Knows What Addresses to Use

Address Short Answer Long Answer

Source MAC On NICGiven to Ethernet NIC by manufacturer; sending host can find MAC on NIC hardware.

Source IP Configuration Either through static configuration or DHCP

Destination MAC

ARPFrom its ARP table, or if not found, by using ARP protocol and sending ARP Request and waiting for ARP Reply from destination

Destination IP

User Either typed or clicked by user

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IP Routing with Layer 1, 2, and 3 Interactions Discovering MAC addresses using ARP: ARP Request

and ARP Reply ARP Request (ARP

Broadcast): Sending device queries for MAC address of destination device; sends Request as broadcast to all other devices on subnet

Example: PC11 wants to send packet to server S1 (in same subnet) but does not know S1’s MAC address; PC11 sends ARP Request to all devices on subnet

Figure 8-43ARP Request (Broadcast)61


ARP Reply: Lists IP address ARP Request asked about with corresponding MAC address of that host

Example: ARP Reply that server S1 makes in response to PC11’s ARP Request

ARP Reply is unicast since ARP Requestgenerated from oneparticular device

Figure 8-44ARP Reply (Unicast)62


Routing data between different subnets

IP packets in network act like person traveling to destination, using all forms of transportation; packet goes from end-to-end

Data Link frames act like individual vehicles used for only part of trip (e.g., just train); frames never leave their own LAN/WAN

Figure 8-45Example, IP Packet End-to-End, Data Link Heads Stay on LAN or WAN63

IP Routing with Layer 1, 2, and 3 Interactions Addressing frames and packets when crossing subnets

example: PC11 (10.1.1.11) sends IP packet to PC21 (10.1.2.21)

Hosts sit on different LANs (may also be in different subnets)

Figure 8-46IP Addresses Stay the Same Through End-to-End Path64


Example: PC11 sends IP packet to PC21

PC11’s logic tells it to send packet to default router because destination is in different network or subnet

PC11 encapsulates packet inside Ethernet frame with destination MAC address R1

Figure 8-47Ethernet Frames Use MAC on that LAN (Only)65

IP Routing with Layer 1, 2, and 3 Interactions Removing/adding Data Link headers: Router removes

IP packet from incoming Data Link frame (de-encapsulation) and then adds new Data Link header and trailer before sending packet (encapsulation)

Steps router goes through:1. De-encapsulates IP packet from inside Data Link frame

2. Makes routing decision using packet’s destination IP address and its own IP routing table, identifying correct outgoing interface

3. Encapsulates packet into new Data Link frame that works on outgoing interface

4. Sends packet through outgoing interface to destination

Figure 8-48Routers Discard Old and Add New Data Link Framing66


Example: When R1 receives packet destined to subnet on R2

Figure 8-48Routers Discard Old and Add New Data Link Framing67


Using ARP with routers: R2 needs to deliver IP packet to host PC21

1. R2 builds Ethernet header with PC21’s MAC address as destination

2. If R2 does not know PC21’s MAC address (i.e., it is not in its ARP table), R2 uses ARP to learn MAC address

3. When R2 receives ARP Reply with PC21’sMAC address, sends frame

Figure 8-49Example of Router R2 Using ARP to Learn a Local Host’s MAC Address68

Summary, This Chapter… Described the main functions of the TCP/IP network

layer in regards to its focus on either physical or logical functions, and the focus on the network or endpoint hosts.

Listed three major functions defined by IP.

Listed common TCP/IP network layer functions in addition to IP.

Examined a figure of an Enterprise TCP/IP network and determine where IP address groups (IP networks or subnets) would be needed.

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Summary, This Chapter… Looked at any IP version 4 address and determined its

class, and if a unicast IP address, determined the class A, B, or C network ID of the network in which it resides.

Listed the four IP settings typically set on IP hosts during static configuration.

Described the layer 3 logic used by routers when routing IP packets.

Described an IP host’s layer 3 logic when routing IP packets.

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Summary, This Chapter… Explained the basic ideas of how the IP subnetting

process subdivides a classful network into smaller groups.

Predicted the MAC and IP addresses used by two hosts on the same LAN subnet when they send IP packets to each other.

Predicted the MAC and IP addresses used throughout an IP packet’s journey from a host in one subnet to a host in another subnet.

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Questions? Comments?

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Documents

NT1210 Introduction to Networking