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1. Chapter 14
TCP/IP and Routing
Part #1
Unix System Administration

2. T.C. P’s and I P’s
 What is TCP/IP?
 TCP/IP is a networking protocol for
transmitting data between computers
 TCP/IP is a family of protocols
 TCP/IP is the protocol of the Internet
 TCP/IP is the default protocol of UNIX
 TCP/IP provides a uniform programming
interface to different types of network
hardware that guarantees interoperability

3. We Are Family
 IP - Internet Protocol which transports
raw data from one machine to another
 ICMP - Internet Control Message
Protocol provides low-level support for
IP such as error messages, routing
assistance and “pings”
 ARP - Address Resolution Protocol
which translates logical address (IP
address) to hardware address (MAC
address)

4. All in the Family
 TCP - Transmission Control Protocol
uses IP to maintain a connection-
oriented sessions between machines
that guarantees delivery of data.
 UDP - User Datagram Protocol uses IP
for connectionless sessions between
machine without the guarantee of data
delivery.

5. So You Want to Date a Model?
 The OSI Model by the ISO
 Seven Layers
– Layer 7 - Application Layer
– Layer 6 - Presentation Layer
– Layer 5 - Session Layer
– Layer 4 - Transport Layer
– Layer 3 - Network Layer
– Layer 2 - Data Link Layer
– Layer 1 - Physical Layer

6. The Government Thought OSI
Was A Good Idea
 The US Government decided all
government computers should use OSI
 OSI had implementation problems
– Relied on concepts that made no sense in
modern networks
– Some specifications were incomplete
– Functionally inferior to existing protocols
– Too many layers which made it slow

7. Back to Good Ol’ TCP/IP in the
Good Ol’ US of A
 Good enough of government work
 TCP/IP has 4 layers
– Layer 4 - Application Layer (think telnet,
ftp, http, etc.)
– Layer 3 - Transport Layer (think TCP/UDP)
– Layer 2 - Network Layer (think IP)
– Layer 1 - Link Layer (think ethernet card)

8. How Does it All Fit Together
Exhibit A from Page 246 in your book

9. Pack-et In a Frame
 Data travels the network in a packet
which consists of a payload and
headers
 Packets are sometimes referred to as
frames when talking about the low-level
transport, (e.g. Ethernet)
 The low-level transport may limit the
size of a frame/packet. This is called
the MTU - maximum transfer unit

10. Sample Packet

11. IP on Your MAC Port?
 Three key addresses determine the
source and destination of a packet
– MAC - low-level address of network
hardware. For Ethernet, 6-byte globally
unique address.
– IP - dotted quad-octet assigned to each
network device. Globally unique.
– Port - two-byte number that specifies a
particular service on a machine

12. Mapping IP to MAC Using ARP
 The ARP protocol is used to map IP
address to MAC addresses
– Machine sends ARP request “Who is
159.91.15.220?”
– The machine or another machine on the
same network will respond
“00:40:95:21:CB:38 is 159.91.15.220”
– The MAC address is used to make the final
delivery of the packet to the destination
machine.

13. Dotted? Quad? Octet?
 IP Address
– Octet = 8-bit number (usually we call this a
byte, but old DEC systems used 7-bit
bytes) = values 0-255
– octet.octet.octet.octet is the format of an
IP address, such as 159.91.15.220
– IP addresses have a structure to their
assignment, where as, MAC addresses
have no relationship to each other

14. IP Address Have Classes Too
 There are 5 classes for IP addresses
– Class A - first octet is assigned as the
network address, the remaining 3 octets
are available for network devices
– Class B - first two octets are assigned as
the network address, remaining 2 octets
are available for network devices
– Class C - first three octets are assigned as
the network address, remaining octet is
available for network devices

15. Going Out With Class
 The last two IP classes are special
– Class D - multicast addresses. This is the
rare case where the multiple machines can
have the same IP address
– Class E - experimental

16. IP Class Summary
Class 1st
Octet Format
A 1-126 N.H.H.H
B 128-191 N.N.H.H
C 192-223 N.N.N.H
D 224-239 -
E 240-254 -

17. Who’s The Head of the
Classes?
 *NOTE* - the book is out of date about this
 Today, you typically get your addresses from
your Internet Service Provider
 Addresses are ultimately controlled by IANA -
Internet Assigned Number Authority. IANA
give certain registries around the globe
authority to give out IP addresses.
www.iana.org
 ARIN - American Registry for Internet
Numbers handles the Americas. www.arin.net

18. IP Privately
 There are private IP addresses set aside
for internal use. They are not routed if
they get to the Internet.
 These private addresses can be used if
you setup a standalone network or if
you will be using NAT (Network Address
Translation) to translate a private
address to a valid public address before
going to the Internet.

19. Still, IP Privately
 RFC1918
– http://www.isi.edu/in-notes/rfc1918.txt
– Class A - 10.0.0.0 thru 10.255.255.255
– Class B - 172.16.0.0 thru 172.31.255.255
– Class C - 192.168.0.0 thru 192.168.255.255

20. What Service Do You Use Your
Port For?
 A port is the location on a particular machine
that a service is running on.
 Think of it as room in a house. The house
has an address (IP), but each room (port)
provides a certain function.
 Ports below 1024 are called “well known”
ports. Only root has access to start services
on these ports.
 Ports 1024 and above are called “ephemeral”
ports. These ports are open to everyone on
the system.

21. What’s That In My #2 Port?
 Normally, a vendor goes to IANA to get
a port assigned to them for their service
to run on. Each service has a unique
port. E.g. - telnet is 23, http is 80.
 RFC1700 used to keep this list, but is
now out-dated.
 See http://www.iana.org/numbers.html
for the most up-to-date list.

22. Why, Why, Y?
 Why would you use a private address
with NAT when connecting to the
Internet instead of getting public
addresses for each machine?
 Why would you use a multicast (class
D) address?

23. Coming Soon to a Lecture
Near You
 Part #2 - Routing and Subnets