Presentation
Title
Subtitle
Introduction to IP
and Routing
Gur Saran Adhar
Author
TM
Copyright © 2002 OPNET Technologies, Inc.
What is IP?
• Connectionless, unreliable, best-efforts packet delivery system
• Connectionless

Just addresses a packet and sends it (analogous to mailing a letter)
 Does not need to create a connection to the destination. That is the responsibility of a
higher layer (like TCP)
• Unreliable

Packets may be lost, delayed, duplicated, out of order, or damaged in transmission
 Up to higher layer to provide reliability
• Best-efforts

Packets will not be discarded arbitrarily, without good cause
• Exhaustion of resources
• Failure of lower layer
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OSI vs. TCP/IP
• The TCP/IP protocol stack does not match the OSI protocol stack
exactly
• TCP/IP in use before OSI protocols appeared
• ARPANET (research network sponsored by DoD) needed

Ability to connect multiple networks together
 Ability to survive loss of subnet hardware, with no connection loss
• Internet layer developed: Can inject packets that travel independently to the
•
destination
One of the first implementation by Berkeley

Good implementation
 Free
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OSI vs. TCP/IP, cont.
• OSI model developed before any implementation
• TCP/IP model developed after it was implemented
• Some companies already had product with TCP/IP
• Did not want to support 2 protocols
• OSI more complex than TCP/IP

Q: What do you get when you cross a mobster with an international standard?
 A: Someone who makes you an offer you can’t understand
• Waited to see how others would use OSI
• TCP/IP became more widespread, while nothing really happened
with OSI
• OSI still used as a first example of a layered protocol stack
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OSI and TCP/IP stacks
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IP Addresses
• IP addresses are analogous to postal addresses
• Destination is described from the general to the specific

Zip code/State -> City -> Street -> Building -> Person
 Network Address -> Host Address
• IP Addresses consist of 4 numbers, separated by periods
• Each number ranges from 0 – 255
• Examples:

12.221.14.2
 192.15.223.111
• Each machine interface on a network has a unique IP Address
• Numbers assigned by the Network Information Center (NIC)
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Dotted Decimal Notation of IP
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IP Subnets
• Subnets are used if you have more machines than IP addresses
• Allows a network to be split into several parts for internal use,
but still act like a single network to the outside world
• IP packets are routed depending on their destination
• Other network: forwarded to next router
• This network: forwarded to internal destination
• Uses “Subnet Mask” to determine internal destination
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IP Addresses : subnet + host address
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IP Datagram format
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IP address and Routing (example IP datagram
arrives at the middle router)
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Routing with IP address
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IP address written in CIDR notation
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Reserved IP addresses
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IP Addresses Classes
• Address classes
• Class A: 1.0.0.0 to 127.255.255.255

126 networks with 16 million hosts each
• Class B: 128.0.0.0 to 191.255.255.255

16,382 networks with 64K hosts each
• Class C: 192.0.0.0 to 223.255.255.255

2 million networks with 254 hosts each
• Class D: (multicast) 224.0.0.0 to 239.255.255.255
• Class E: 240.0.0.0 and up: reserved for future use
• 127.xx.yy.zz is a “loopback” address

Not actually sent on the wire
 Processed locally, as an incoming packet
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Dynamic Host Configuration Protocol (DHCP)
• Alternative to “static” IP Addresses
• Allows for even more hosts within a subnet
• Major downfall is that you cannot host a service easily
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Host names
• Familiar names are easier to remember than IP Addresses
• Names can be registered (internic)
• .net, .com, .gov, .au, .fr, etc
• e.g. www.amazon.com, www.opnet.com
• “Ping” a host name to get its IP Address
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Domain Name System (DNS)
• A DNS server keeps track of the meaning of host and domain
names
• Even without DNS, you can get to other internet locations, using
the IP Address
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IP Quality of Service (QoS)
• Some applications require different service than others
• Considerations:
• Connection establishment delay
• Connection establishment failure probability
• Throughput
• Transit delay
• Residual error ratio
• Protection
• Priority
• Delay variation
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IP Security (IPsec)
• Developing standard for security at the network layer
• Earlier security approaches have inserted security at the
application layer
• Useful for implementing
• Virtual Private Networks (VPNs)
• Remote user access through dial-up connection to private networks
• Security arrangements can be handled without requiring changes
to individual user computers.
• Cisco has been a leader in proposing IPsec as a standard (or
combination of standards and technologies) and has included
support for it in its routers
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IP Routing
• Many different routing algorithms
• Static
• Routes decided in advance
• Not adaptive to network changes
• Dynamic
• Change routing decisions to reflect changes in topology and traffic
• Adaptive to network changes
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