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ES 101. Module 2
IP 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 Values
First 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