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Semester 2v2
Chapter 9: TCP/IP
List three components of the TCP/IP protocol stack.
•protocols to support file transfer, e-mail, remote login, and other applications
•reliable and unreliable transports
•connectionless datagram (packet) delivery at the network layer
ICMP provides control and message functions at the network layer.
The Transmission Control Protocol/Internet Protocol (TCP/IP) suite of protocols was developed
by the Defense Advanced Research Projects Agency (DARPA).
The suite includes not only Layer 3 and 4 specifications (such as IP and TCP), but also
specifications for such common applications as e-mail, remote login, terminal emulation, and
file transfer.
Later, TCP/IP was included with the Berkeley Software Distribution of UNIX.
You can use the Internet protocols to communicate across any set of interconnected networks.
They are equally well-suited for both LAN and WAN communication.
The TCP/IP protocol stack maps closely to the OSI reference model in the lower
layers. It supports all standard physical and data link protocols.
TCP/IP information is transferred in a sequence of datagrams. One message may
be transmitted as a series of datagrams that are reassembled into the message at
the receiving location.
The application layer supports network management. It has
protocols for file transfer, e-mail, and remote login.
The transport layer performs
two functions –
flow control, provided by
sliding windows
reliability, provided by
sequence numbers and
acknowledgments.
The transport layer also provides
two protocols:
•TCP - a connection-oriented, reliable protocol; provides flow control by
providing sliding windows, and reliability by providing sequence numbers and
acknowledgments. The advantage of TCP is that it provides guaranteed delivery
of the segments
•UDP - connectionless and unreliable; although responsible for transmitting
messages, no software checking for segment delivery is provided at this layer.
The advantage that UDP provides is speed.
•source port - the number of the
calling port
•destination port - the number
of the called port
•sequence number - the
number used to ensure correct
sequencing of the arriving
data
•acknowledgment number the next expected TCP octet
•HLEN - the number of 32-bit
words in the header
•reserved - set to 0
•code bits - the control functions (e.g. setup and termination of a session)
•window - the number of octets that the sender is willing to accept
•checksum - the calculated checksum of the header and data fields
•urgent pointer - indicates the end of the urgent data
•option - one currently defined: maximum TCP segment size
•data - upper-layer protocol data
Both TCP and UDP use port (or socket)
numbers to pass information to the
upper layers.
Port numbers are used to keep track of
the different conversations that cross
the network at the same time.
Application software developers have
agreed to use the well-known port
numbers that are defined in RFC
1700. For example, any conversation
bound for an FTP application uses the
standard port number 21.
Conversations that do not involve an
application with a well-known port
number are, instead, assigned port
numbers that are randomly selected
from within a specific range. These
port numbers are used as source and
destination addresses in the TCP
segment.
Some ports are reserved in both TCP and UDP, although applications might not be written to support
them. Port numbers have the following assigned ranges:
Numbers below 255 are for public applications.
Numbers 255-1023 are assigned to companies for marketable applications.
• Numbers above 1023 are unregulated.
End systems use port numbers to select the proper application.
Originating source port numbers, usually some numbers larger
than 1023, are dynamically assigned by the source host
Host A -- seq =n
Host B -- seq= n+1
Both ends of a connection are synchronized with a three-way
handshake/open connection sequence. Exchanging beginning
sequence numbers during the connection sequence ensures that
lost data can be recovered if problems occur later
Window size determines how much data a
receiving station can accept at one time. With a window size of
1(byte), each segment that you send must be acknowledged before
you can transmit another segment.
This results in inefficient use of bandwidth by the hosts.
Window size refers to the number of
bytes (or octets) that a host can
transmit while awaiting an
acknowledgment.
A larger window size allows the host
to transmit more data pending
acknowledgment.
After it transmits the window-size number of bytes, it must receive an acknowledgment
before it can send more messages.
TCP uses expectational acknowledgments, meaning that the acknowledgment number
refers to the octet that is expected next.
The sliding part of sliding window refers to the fact that the window size is negotiated
dynamically during the TCP session.
A sliding window provides more efficient use of bandwidth by the hosts.
TCP provides sequencing of segments with a forward reference acknowledgment. Each
datagram is numbered before transmission.
At the receiving station, TCP reassembles the segments into a complete message. If a
sequence number is missing in the series, that segment is retransmitted.
If segments are not acknowledged within a given time period, retransmission occurs
Application layer protocols must provide for reliability if necessary. UDP uses no
windowing or acknowledgments.
It is designed for applications that do not need to put sequences of segments together.
Protocols that use UDP include the following:
•TFTP
•SNMP
•Network File System (NFS)
•Domain Name System (DNS)
Several protocols operate at the TCP/IP Internet layer that corresponds to the OSI
network layer:
•IP - provides connectionless, best-effort delivery routing of datagrams; is not
concerned with the content of the datagrams; looks for a way to move the
datagrams to their destination
•ICMP - provides control and messaging capabilities
•ARP - determines the data link layer address for known IP addresses
•RARP - determines network addresses when data link layer addresses are known
The fields in this IP datagram are as follows:
•VER - version number
•HLEN - header length, in 32-bit words
•type of service - how the datagram should be
handled
•total length - total length (header + data)
•identification, flags, frag offset - provides
fragmentation of datagrams to allow
differing MTUs in the internetwork
•TTL - Time-To-Live
•protocol - he upper-layer (Layer 4) protocol
sending the datagram
•header checksum - an integrity check on the
header
•source IP address and destination IP address
- 32-bit IP addresses
•VIP options - network testing, debugging,
security, and other options
The protocol field
determines the Layer 4
protocol being carried
within an IP datagram.
Although most IP traffic
uses TCP, other protocols
can also use IP.
Each IP header must identify the destination Layer 4 protocol for
the datagram.
Transport layer protocols are numbered, similarly to port
numbers. IP includes the protocol number in the protocol field.
•Destination Unreachable
•Time to Live Exceeded
•Parameter Problem
•Source Quench
•Redirect
•Echo
•Echo Reply
•Timestamp
•Timestamp Reply
•Information Request
•Information Reply
•Address Request
•Address Reply
ICMP is implemented by all TCP/IP hosts.
ICMP messages are carried in IP datagrams and are used to send
error and control messages.
If a router receives a packet that it is unable to deliver to its final
destination, the router sends an ICMP unreachable message to
the source.
The message might be undeliverable because there is no known
route to the destination
An echo reply is a successful reply to a ping command; however, results
could include other ICMP messages, such as unreachable and timeout
messages
ARP is used to resolve
or map a known IP
address to a MAC
sublayer address in
order to allow
communication on a
multi-access medium
such as Ethernet.
To determine a destination MAC address for a datagram, a table called the ARP cache
is checked. If the address is not in the table, ARP sends a broadcast that will be
received by every station on the network, looking for the destination station.
The term "local ARP" is used to describe the search for an address when the
requesting host and the destination host share the same medium or wire.
Prior to issuing the ARP, the subnet mask must be consulted. The mask determines
that the nodes are on the same subnet.
RARP relies on the
presence of a RARP
server with a table
entry or other
means to respond to
requests.
On the local
segment, you can
use RARP to
initiate a remote
operating system
load sequence.
Internet protocols enable
communications between
any set of interconnected
networks. They are
equally well suited for
both LAN and WAN
communications,
TCP/IP is the de facto
standard for internetwork
communications and serves as
the transport protocol for the
Internet, enabling millions of
computers to communicate
globally.
The function of the TCP/IP
protocol stack, or suite, is the
transfer of information from
one network device to
another.
The layers most closely affected by TCP/IP are Layer 7 (application), Layer 4
(transport), and Layer 3 (network).
DNS (Domain Name System) is a system used in
the Internet for translating names of network
nodes into addresses
WINS (Windows Internet Naming Service)
is a Microsoft-developed standard for
Microsoft Windows NT that automatically
associates NT workstations with Internet
domain names.
HOSTS is a file created by network administrators and maintained on servers. They are
used to provide static mapping between IP addresses and computer names.
POP3 (Post Office Protocol) is an Internet standard for storing e-mail on a mail server
until you can access it and download it to your computer. It allows users to receive
mail from their inboxes using various levels of security.
SMTP (Simple Mail Transport Protocol) governs the transmission of e-mail over
computer networks. It does not provide support for transmission of data other than
plain text.
SNMP (Simple Network Management Protocol) is a protocol that provides a means to
monitor and control network devices, and to manage configurations, statistics
collection, performance and security.
FTP (File Transfer Protocol) is a reliable connection-oriented service that uses TCP to
transfer files between systems that support FTP. It supports bi-directional binary file
and ASCII file transfers
TFTP (Trivial File Transfer Protocol) is a connectionless unreliable service that uses
UDP to transfer files between systems that support the TFTP. It useful in some LANs
because it operates faster than FTP in a stable environment.
HTTP (Hypertext Transfer Protocol) is the Internet standard that supports the
exchange of information on the World Wide Web, as well as on internal networks. It
supports many different file types, including: text, graphic, sound , and video.
It defines the process by which Web browsers originate requests for information to
send to Web servers.
Telnet is a standard terminal emulation protocol used by clients for the purpose of
making remote terminal connections to Telnet server services; enables users to
remotely connect to routers to enter configuration commands.
PING (Packet Internet Groper) is a diagnostic utility used to determine whether a
computer is properly connected to devices/Internet.
Traceroute is a program that is available on many systems, and is similar to PING,
except that traceroute provides more information than PING. Traceroute traces the
path a packet takes to a destination, and is used to debug routing problems
There are also a few Windows-based protocols that you should be familiar with:
•NBSTAT - a utility used to troubleshoot NetBIOS name resolution; used to view
and remove entries from the name cache
•NETSTAT - a utility that provides information about TCP/IP statistics; can be
used to provide information about the status of TCP/IP connections and
summaries of ICMP, TCP, and UDP
•ipconfig/winipcfg - utilities used to view current network settings for all adapters
on a device; can be used to view the MAC address, IP address, and gateway
The END