ES 101. Module 2IP Addressing & Routing

Last Lecture

• Wide area networking• Definition of “packets”

This Lecture

• TCP/IP Architecture• Internetworking/routing• Internet Protocol (IP)

History

• TCP/IP was first developed by the Advanced Research Projects Agency (ARPA) in 1969, and implemented as a test internetwork– Known as the “ARPANET”

– ARPA is now known as DARPA

• The ARPANET was originally utilized to interconnect a small number of government agencies and universities

• ARPANET has evolved into what we now know as the Internet

Internetworking Definition

• Link multiple local area networks (LANs) together• Route and deliver data between devices on different

local area networks• These mechanisms are provided by the TCP/IP

protocols, which are divided into different protocol “layers”

TCP/IP Protocol Suite

Layer 5

Layer 4

Layer 3

Internetworking

• The Internet is composed of a “network of networks” interconnected by routers

• Routers determine how to forward packets to the destination computer

• This routing is accomplished via two types of addressing:– Network Number

– Computer (host) number on a given network

Internetworking Architecture

Internetworking Schematic

PSTN

Internet Protocol (IP)

• IP Version 4 (IPv4) is utilized today• Understanding IP addressing is fundamental to

understanding routing• We must understand network numbers, and IP

addressing before we proceed any further

IP Address Format

• We will first review IP addressing in order to understand how the routing process works

• IP utilizes a 32 bit (4 octet) source and destination address

• IP addresses identify both the network number and the host address– This is accomplished via a “subnet mask”

– More on this later….

• IP addresses are commonly expressed in “dotted decimal” notation

For humans, dotted decimal notation is easier to remember than a 32 bit binary number!!!

IPv4 Header

IP Address Usage

• IP addresses are global• These IP addresses are managed by the Internet

Assigned Number Authority (IANA)– www.iana.org

• Blocks of addresses are assigned to organizations like Vanderbilt

• This allows a unique IP address and network number to be assigned to each host and network on the Internet

Dotted Decimal Notation

• The 32 bit address is divided into four octets of 8 bits, with each octet written as a decimal number– Each octet can have a value from 0 to 255

• 28 = 256, with numbers ranging from “0” decimal to “255” decimal

– Example: 194.62.23.2

• Part of the binary IP address is utilized to define the Network ID

• The remainder of the binary address is utilized to indicate the Host ID

• The net mask defines the boundary between the Network ID and the Host ID

Net Masks

• It is necessary to determine where the network address ends, and the host address begins

• This is accomplished by the use of a net mask– Net masks are indicated by the use of “255” and “0” in dot-

decimal notation• “255” decimal equals “11111111” binary• “0” decimal equals “00000000” binary

– Example: 255.255.255.0

• This designation allows easy determination of network numbers and host IDs by a “bitwise and” mathematical operation

Subnet and Host ID Determination

Network Classes

• The IETF defined network address “classes”– Organizations originally registered for IP address space, and were

assigned an address class, based on their anticipated IP usage

– This is no longer the case, since IP addresses are becoming scarce• This subject is beyond the scope of this class

• Default IP address classes:– Class A Subnet Mask = 255.0.0.0 (3 octets for Hosts)

– Class B Subnet Mask = 255.255.0.0 (2 octets for Hosts)

– Class C Subnet Mask = 255.255.255.0 (1 octet for Hosts)

• Some bits in the host and network address space are reserved

Network Class Usage

• Classes A, B, and C are the most common• Class D is reserved for multi-casting• Class E is reserved for experimentation and

development

Default Network Address Formats

Class Address Ranges

First Octet of the Network Address

Note: 0.X.Y.Z, 127.X.Y.Z, and 255.X.Y.Z are all reserved

Reserved IPv4 Address ValuesFirst Octet

• Decimal 255 (all binary 1s) is used for net masking as discussed previously

• Decimal 127 is used for the loopback, or localhost address– Helps in troubleshooting

Introduction to Routing

• Routers are essentially the “post office” of the Internet• IP packets are best viewed as a “post card”

– Source address– Destination address

• You drop your post card into a mailbox, and it comes out at the destination– You don’t care how it gets there– Routers determine where to send packets by “routing tables”

• The IP address is composed of two parts– Host ID (analogous to the street address)– Network number (analogous to the zip code)

Default Gateway

• Routers are sometimes known as “gateways”• In order for your computer to transfer information

to another machine, it must have a “default gateway” in the network settings

• If the computer needs to send info to foreign networks, it sends the info to the default gateway

• The network of routers handles everything from there

Internetwork Example

Routing Table Rules

• If a network is locally attached, no “Next Router” information is entered for that network number in the routing table

• If a network is not locally attached, the router must “know” what the next hop in the route is– This next hop IP address is entered into the routing table

– This can be done automatically or dynamically• Dynamic routing is beyond the scope of this class

• Each router has a routing table, which defines the next hop IP address for all network numbers on the Internet

Routing Table Example

Routing Tables - Router 1

Routing Tables - Router 2

Routing Tables - Router 3

Next Lecture(s)

• Domain Name System• Higher layer protocols