Download Introduction Lecture 1

Babu Ram Dawadi
 TCP/IP
is a set of protocols developed to allow
cooperating computers to share resources
across a network.
 TCP stands for “Transmission Control Protocol”
 IP stands for “Internet Protocol”
 They are Transport layer and Network layer
protocols respectively of the protocol suite
 The most well known network that adopted
TCP/IP is Internet – the biggest WAN in the
world
A
protocol is a collection of rules and
procedures for two computers to
exchange information
 Protocol
also defines the format of data
that is being exchanged
 TCP/IP
was developed very early
 Technologies
were widely discussed and
circulated in documents called “Request
for Comments” (RFC) – free of charge
 Supported
by UNIX operating system

Because TCP/IP was developed earlier than the
OSI 7-layer mode, it does not have 7 layers but only
4 layers
Application
Transport
Internet
Host Network
 Application
layer protocols define the rules
when implementing specific network
applications
 Rely on the underlying layers to provide
accurate and efficient data delivery
 Typical protocols:
• FTP – File Transfer Protocol
• Telnet – Remote terminal protocol
• SMTP – Simple Mail Transfer Protocol
• HTTP – Hypertext Transfer Protocol


TCP/IP is built on “connectionless” technology, each
datagram finds its own way to its destination
Transport Layer protocols define the rules of
• Dividing a chunk of data into segments
• Reassemble segments into the original chunk

Typical protocols:
• TCP – Transmission Control Protocol
 Provide further the functions such as reordering and data resend
• UDP – User Datagram Service
• Use when the message to be sent fit exactly into a datagram
• Use also when a more simplified data format is required
 Network
layer protocols define the rules of how
to find the routes for a packet to the destination
 It only gives best effort delivery. Packets can be
delayed, corrupted, lost, duplicated, out-oforder
 Typical protocols:
• IP – Internet Protocol
 Provide packet delivery
• ARP – Address Resolution Protocol
 Define the procedures of network address / MAC address
translation
• ICMP – Internet Control Message Protocol
 Define the procedures of error message transfer
Application
Transport
Nework
Host-to-Network
 The
underlying layers have guaranteed
accurate data delivery
 We need to make a lot of agreements
with the server in application layer
before sending mail
1. Agree on how data is represented
• Binary or ASCII
2. Ensure the right recipient
• There may be 1000 users served by the server
3. Ensure the client has the right to send mail
• Some clients are not welcome
4. How to tell the server it is the end of the message
• All mail looks the same
 The
following mail is to be sent:
Date: Fri, 18 Jan 09 13:26:31 EDT
From: [email protected]
To: [email protected]
Subject: meeting
Let’s get together Monday at 1pm.
Client
Server
Access Port No 25 of Server
220 stad.edu SMTP Service
at 20 Jan 09 05:17:18 EDT
HELO ioe.edu.np
250 stad.edu – Hello,
ioe.edu.np
MAIL From:
<[email protected]>
250 MAIL accepted
Client
Server
Access Port No 25 of Server
RCPT to: <[email protected]>
250 Recipient accepted
DATA
354 Start mail input;
end with .
Date: Fri, 18 Jan 09 13:26:31 EDT
From: [email protected]
To: [email protected]
Subject: meeting
Let’s get together Monday at 1pm.

The agreement made in the SMTP protocol
• All messages use normal text
 All ASCII characters
• The responses all begin with numbers
 To indicate the status when receiving the command
• Some words are reserved words
 HELO, MAIL, RCPT…
• Mail ends with a line that contains only a period

The information passed with the SMTP messages
• The recipient name
• The sender name
• The mail
 Every
computer has a network address
• e.g. 158.132.161.99
 To
access a computer, we need to specify its
network address
 Human beings are weak in memorizing
numbers
 We prefer computer name or domain name
• e.g. v6gate.ioe.edu.np
 Need
a machine on the Internet to convert
name to number
 Example:
v6gate.ioe.edu.np
Computer
Name
The domain within edu.np
One of the educational
institutions in NP
The domain within NP
Note: edu.np is not the
same as edu
Root domain name
other examples:
com – commercial
company
org – general organization
net – major network
centre
gov – government org.
mil – militrary group
edu – education org.
 An
organization needs to register its
domain name
• e.g. ioe has registered its name to the domain of
edu.np
 Once
a domain name is assigned, the
organization is free to assign other names
belong to its domain
• e.g. we can have
 election.ioe.edu.np
 Fsu.ioe.edu.np
 mail.ioe.edu.np
 ----
 Nevertheless, such
a complicated
procedure needs not perform in most
cases
 Client computers usually remember the
answers that it got before (DNS Cache)
 It reduces the loading to the root DNS
 To further reduce loading, there can be
many root DNS on the Internet
• e.g. there are a few “com” root DNS
TCP - Transmission control protocol
 TCP is a connection-oriented protocol

• Does not mean it has a physical connection between
sender and receiver
• TCP provides the function to allow a connection virtually
exists – also called virtual circuit

TCP provides the functions:
• Dividing a chunk of data into segments
• Reassembly segments into the original chunk
• Provide further the functions such as reordering and data
resend

Offering a reliable byte-stream delivery service
 A Typical
Procedure
• Sender
 TCP divides a message into segments
 Add sequence no.
 Send the segments in sequence and wait for
acknowledgement
 If an acknowledgement for a segment is not received for a
certain period of time, resend it until an acknowledgement is
received
• Recipient
 When receiving segments, send the acknowledgement with
correct number
 Reassembly the segments back to the message
A
computer may perform a number of
network applications at the same time
• FTP + SMTP + HTTP, etc.
 Each
computer has only one network
address, how can it serve so many
applications at the same time?
• Port multiplexing.
 Some
port numbers are reserved for some
purposes
• Port 21: FTP – file transfer
• Port 25: SMTP – mail transfer
• Port 23: TELNET – remote login
• Port 80: HTTP – Web access
 These
port numbers are well known to all
computers in the network
 E.g. whenever a client access port 25 of the
server, it means the client needs SMTP service
ping
application
HTTP
Telnet
FTP
TCP
DNS
SNMP
Application
Layer
Transport
Layer
UDP
Routing Protocols
ICMP
RIP
IP
IGMP
Network
Layer
OSPF
DHCP
ARP
30
PIM
Ethernet
Network
Interface
Data Link
Layer
 An
entity of a particular layer can only
communicate with:
1. a peer layer entity using a common protocol (Peer
Protocol)
2. adjacent layers to provide services and to receive
N+1 Layer Protocol
N+1 Layer
N+1 Layer
services
N+1 Layer
Entity
Entity
layer N+1/N
interface
N Layer
N Layer
Entity
N Layer Protocol
N Layer
Entity
N-1 Layer
Entity
N-1 Layer Protocol
N-1 Layer
Entity
layer N/N-1
interface
N-1 Layer
31
A layer N+1 entity sees the lower layers only
as a service provider
N+1 Layer
Entity
N+1 Layer Peer Protocol
Indicate
Delivery
Request
Delivery
Service Provider
32
N+1 Layer
Entity
A
service user accesses services of the
service provider at Service Access
Points (SAPs)
 A SAP has an address that uniquely
identifies where the service can be
Layer-N
accessed
N Layer
Entity
Layer
N-1
SAP
layer N/N-1
service interface
N-1
Layer
33
Layer- N-1
Entity


The unit of data send between peer entities is called a Protocol
Data Unit (PDU)
For now, let us think of a PDU as a single packet
A


N Layer
Entity
PDU
(at layer N)
N Layer
Entity
B
Scenario: Layer-N at A sends a layer-N PDU to layer-N at B
What actually happens:
• A’s layer-N passes the PDU to one the SAPs at layer-N-1
• Layer-N-1 entity at A constructs its own (layer-N-1) PDU which it sends
to the layer-N-1 entity at B
• PDU at layer-N-1 = layer-N-1 Header + layer –N PDU
34
A
B
Layer-N
Entity
control
Layer-N PDU and control data is
sent to SAP of Layer-N-1
Layer-N
Entity
N PDU
SAPs
Layer- N-1
Entity
Layer- N-1
Entity
Header
control
N PDU
(of layer N-1)
N PDU
PDU of Layer-N-1
35
HTTP
HTTP protocol
HTTP
TCP
TCP protocol
TCP
IP
Ethernet
Ethernet
argon.tcpiplab.edu
128.143.137.144
36
IP
IP protocol
Ethernet
IP protocol
Ethernet
Ethernet
router71.tcpip- router137.tcpiplab.edu
lab.edu
128.143.137.1
128.143.71.1
00:e0:f9:23:a8:20
IP
Ethernet
neon.tcpip-lab.edu
128.143.71.21
HTTP
TCP
IP
Frame is an IP
datagram
Ethernet
Send HTTP Request
to neon
Establish a connection to 128.143.71.21 at
port 80Open TCP connection to
128.143.71.21 port 80
IP datagram is a TCP
segment for port 80
Send
IP data-gram
to
Send a datagram (which
contains
a connection
Send IP datagram
to
IP
128.143.71.21
request) to 128.143.71.21
128.143.71.21
Frame is an IP
datagram
Send the datagram to 128.143.137.1
Ethernet
Ethernet
HTTP
TCP
IP
Send the datagram
Ethernet
to 128.143.7.21
argon.tcpipneon.tcpip-lab.edu
router71.tcpip- router137.tcpipSend Ethernet frame
Send Ethernet frame
lab.edu
128.143.71.21
lab.edu
to 00:20:af:03:98:28
to 00:e0:f9:23:a8:20 lab.edu
128.143.137.144
128.143.137.1
128.143.71.1
00:e0:f9:23:a8:20
37
 Different
Layers of the protocol stack have a
different view of the network. This is HTTP’s and
TCP’s view of the network.
Argon
128.143.137.144
HTTP client
HTTP
server
HTTP
server
TCP client
TCP server
TCP server
IP Network
38
Neon
128.143.71.21
128.143.137.144
128.143.71.21
128.143.137.1
128.143.71.1
Router
128.143.137.0/24
Network
39
128.143.71.0/24
Network
 Ethernet’s
40
view of the network
 IP
(Version 4) Addresses are 32 bits
long
 IP Addresses Assigned Statically or
Dynamically (DHCP)
 IPv6 addresses are 128 bits long
4
8-bit numbers (Hierarchical)
18.26.0.1
network
32-bits
 Specifies
host
both network and host
 Number of bits allocated to specify network
varies
 Three classes:
A
0 net
1 7
B
host
24 bits
C
1 0 net
host
110
net
host
2
16 bits
3
21
8 bits
14






IPv4 address: a 32-bit number, usually written in dotted
decimal form, that uniquely identifies an interface of
some computer
Host Address: another term for IP address
Network: a group of hosts, all of which have an identical
beginning position of their ip addresses.
Network Number: a 32-bit number that represent a
network and it cant be assigned as ip address of a host
Network address: another term for the network
number.
Broadcast address: a 32-bit number that is used to
address all hosts in the network. It cant be assigned as
an ip address of a host.
Subnet: a group of hosts, all of which have an
identical portion of their ip addresses, a subnet
differs from a network in that a subnet is a further
subdivision of a network.
 Subnet number: a 32-bit number that represent a
subnet. It cant be assigned as ip address of host.
 Subnet address: another term for the subnet
number.
 Subnet broadcast address: a 32-bit number, that
is used to address all hosts in the subnet. It cant
be assigned into an host’s ip address.

Subnetting: the process of subdividing networks
into smaller subnets.
 Subnet mask: A 32-bit combination used to
describe which portion of an address refers to
the subnet and which part refers to the host.
 Network mask: 32-bit number. The mask is used
by computers to calculate the network number of
a given IP address by performing a Boolean AND
operation of the address and mask.
 Address mask: another term for a mask
 Interface: A network connection.




Class A: 255.0.0.0
Class B: 255.255.0.0
Class C: 255.255.255.0
Class A IP_Addr
8.20.15.1 =
00001000.00010100.00001111.00000001
255.0.0.0 =
11111111.00000000.00000000.00000000
----------------------------------Class A
net id |
host id
Mask
netid = 00001000 = 8
hostid = 00010100.00001111.00000001 =
20.15.1
 Subnetting
allows you to create multiple logical
networks that exist within a single Class A, B, or
C network
 When sub-netting, a third part of IP address
appears in the middle of the address—namely,
the subnet part of the address. The size of the
network part never shrinks.
Network (8)
Subnet (24-x)
Host (x)
Class A
Network (16)
Subnet (16-x)
Host (x)
Class B
Network (24)
Subnet (8-x)
Host (x)
Class C
 given
a Class C network of 204.17.5.0 which has a
natural mask of 255.255.255.0, you can create
subnets in this manner:
204.17.5.0 11001100.00010001.00000101.00000000
255.255.255.224 11111111.11111111.11111111.11100000
--------------------------|sub|---With these three subnetbits, it is possible to create
eight subnets









With the remaining five host ID bits, each subnet can have
up to 32 host addresses:
204.17.5.0 255.255.255.224 host address range 1 to 30
204.17.5.32 255.255.255.224 host address range 33 to 62
204.17.5.64 255.255.255.224 host address range 65 to 94
204.17.5.96 255.255.255.224 host address range 97 to 126
204.17.5.128 255.255.255.224 host address range 129 to 158
204.17.5.160 255.255.255.224 host address range 161 to 190
204.17.5.192 255.255.255.224 host address range 193 to 222
204.17.5.224 255.255.255.224 host address range 225 to 254
 the
mask of 255.255.255.224 can also be
denoted as /27 as there are 27 bits that
are set in the mask
 This second method is used with CIDR
 For example, 204.17.5.32/27 denotes the
network 204.17.5.32 255.255.255.224.
 Given
the network number and a mask,
how many subnets are there and how
many hosts per subnet.
 Given an address and mask, what is the
subnet number
 Given an address and mask, what is the
subnet broadcast address and valid ip
address on the subnet
 Subnet bits=32-(network bits+ hosts bits)
8.1.4.5/16
130.4.102.1/24
199.1.1.100/24 130.4.102.1/22
199.1.1.100/27
Mask
255.255.0.0
255.255.255.0
255.255.255.0
255.255.252.0
255.255.255.224
Network bits
8
16
24
16
24
Hosts bits
16
8
8
10
5
Subnet bits
8
8
0
6
3
28-2
28-2
210-2
25-2
hosts per subnets 216-2
No. of subnets
28-2
28-2
0
26-2
23-2
Subnet number
8.1.0.0
130.4.102.0
199.1.1.0
130.4.100.0
199.1.1.96
1st valid IP addr.
8.1.0.1
130.4.102.1
199.1.1.1
130.4.100.1
199.1.1.97
Broadcast addr.
8.1.255.255
130.4.102.255
199.1.1.255
130.4.103.255
199.1.1.127
Last valid addr.
8.1.255.254
130.4.102.254
199.1.1.254
130.4.103.254
199.1.1.126
 Given
the Class C network of
204.15.5.0/24, subnet the network in
order to create the network in Figure 3
with the host requirements shown.
 netA: must
support 14 hosts
 netB: must support 28 hosts
 netC: must support 2 hosts
 netD: must support 7 hosts
 netE: must support 28 host
VLSM!!!

Determine what mask allows the required number
of hosts.
• netA: requires a /28 (255.255.255.240) mask to support 14
•
•
•
•

hosts
netB: requires a /27 (255.255.255.224) mask to support 28
hosts
netC: requires a /30 (255.255.255.252) mask to support 2
hosts
netD*: requires a /28 (255.255.255.240) mask to support 7
hosts
netE: requires a /27 (255.255.255.224) mask to support 28
hosts
* a /29 (255.255.255.248) would only allow 6
usable host addresses therefore netD requires a
/28 mask.
 The
easiest way to assign the subnets is
to assign the largest first. For example,
you can assign in this manner:
 netB: 204.15.5.0/27 host address range 1
to 30
 netE: 204.15.5.32/27 host address range
33 to 62
 netA: 204.15.5.64/28 host address range
65 to 78
 netD: 204.15.5.80/28 host address range
81 to 94
 netC: 204.15.5.96/30 host address range
VLSM!!!
97 to 98

Given network: 202.70.100.0/24, subnet the network in
order to create the network in figure below with the
host requirements shown.
Net A: 13 Hosts
Net D: 29 Hosts
Net B: 2 Hosts
Net C: 6 Hosts
Net E: 14 Hosts
Net F: 2 Hosts
Net G: 5 Hosts
Net G: 24 Hosts
 Originally, 3
Classes
• A, B, C
 Problem
• Classes too rigid (C too small, B too big)
 Solution
• Subnetting
• Classless Interdomain Routing (CIDR)
 Routers
are not omniscient
• Next-Hop
 Hop-by-Hop
 Thus
IP makes no guarantees
• except to try it’s best (”Best Effort”)
• packets may get there out of order, garbled,
duplicated
• may not get there at all!
• Unreliable datagram service
128.17.20.1
1
R1 2
3
R2
R3
R4
128.17.16.1
e.g. 128.9.16.14 => Port 2
Prefix
65/8
128.9/16
128.9.16/20
128.9.19/24
128.9.25/24
128.9.176/20
142.12/19
Next-hop
128.17.16.1
128.17.14.1
128.17.14.1
128.17.10.1
128.17.14.1
128.17.20.1
128.17.16.1
Port
3
2
2
7
2
1
3
Forwarding/routing table
How a Router Forwards Datagrams
0
232-1
128.9.0.0
65/8
0
128.9.16.14
142.12/19
128.9/16
216
232-1
128.9.19/24
128.9.25/24
128.9.16/20 128.9.176/20
128.9/16
0
232-1
128.9.16.14
128.9.19/24
128.9.25/24
128.9.16/20 128.9.176/20
128.9/16
0
232-1
128.9.16.14
Protocol Stack
App
Transport
TCP / UDP
Network
IP
Link
Data
Data
TCP Segment
Hdr
Hdr
IP Datagram
 Connection-Oriented
 Reliable
 Byte-Stream
 Flow
Control
(aka Congestion Control)
 Establish
Connection
 Data Transfer
 Terminate Connection
(Active)
Client
Syn
(Passive)
Server
Syn + Ack
Ack
Connection Setup
3-way handshake
Host A
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
Host B
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
Host A
TCP Data
Host B
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
TCP Data
Byte 80
Byte 3
Byte 2
Byte 1
Byte 0
IP Data
TCP Data
0
TCP Hdr
15
Src port
31
Dst port
Sequence #
Ack Sequence #
RSVD
6
Flags
URG
ACK
PSH
RST
SYN
FIN
HLEN
4
Checksum
IP Hdr
Window Size
Urg Pointer
(TCP Options)
TCP Data
Src/dst port numbers
and IP addresses
uniquely identify socket
(Active)
Client
Fin
(Passive)
Server
(Data +) Ack
Fin
Ack
Connection Close/Teardown
2 x 2-way handshake
 Connection-Oriented
 Reliable
 Byte-Stream
 Flow
Control
(aka Congestion Control)
 Sequence
numbers &
Acknowledgements (ACKs)
• Receiver detects Corrupt, Lost, Duplicated, Out-
of-order
• Tell sender which packets it has received
correctly
• Sender can resend
 In
Flight Window (Window Size)
• Sender only has N unacknowledged packets “in
Leland.Stanford.edu
Application Layer
Arachne.Berkeley.edu
Leslie
Ron
Transport Layer
O.S.
D
Data
Header
Data
O.S.
Header
Network Layer
H
D
H
D
D
H
H
D
D
H
Link Layer
H
Protocol Stack
App
Transport
TCP / UDP
Network
IP
Link
Data
Data
TCP Segment
Hdr
Hdr
IP Datagram
 Like
TCP, in the Transport Layer
 Characteristics
• Connectionless, Datagram, Unreliable
 Adds
only application
multiplexing/demultiplexing and
checksumming to IP
 Good for Streaming Media, Real-time
Multiplayer Networked Games, VoIP




79
Data Link Layer:
• Service:
Reliable transfer of frames over a link
Media Access Control on a LAN
• Functions:
Framing, media access control, error checking
Network Layer:
• Service:
Move packets from source host to destination
host
• Functions:
Routing, addressing
Transport Layer:
• Service:
Delivery of data between hosts
• Functions:
Connection establishment/termination, error
control, flow control
Application Layer:
• Service:
Application specific (delivery of email, retrieval
of HTML
documents, reliable transfer of file)
• Functions:
Application specific
 IP
is the basis of Internetworking
 TCP builds on top of IP
adds reliable, congestion-controlled,
connection-oriented byte-stream.
 UDP builds on top of IP
allows access to IP functionality