Download CCNA2 3.0-10 Intermediate TCPIP

Cisco 2 - Routers
Chapter 10
TCP/IP Protocol Suite
The function of the TCP/IP protocol stack is to transfer information from
one network device to another.
In doing so, it closely maps the OSI reference model in the lower layers and
supports all standard physical and data link protocols.
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Cisco 2 - Routers
Chapter 10
TCP/IP and Application Layer
The application layer of the TCP/IP combines the functionality found in the
OSI :
• application
• presentation
• session layers
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Cisco 2 - Routers
Chapter 10
TCP/IP and Application Layer
The protocols of TCP/IP that support file transfer, e-mail and remote login,
include the following:
• Domain Name System (DNS) – translate domain name to IP address
• HOSTS – supports static mappings between IP & computer names
• Post Office Protocol (POP3)
• Simple Mail Transfer Protocol (SMTP)
• Simple Network Management Protocol (SNMP) – monitor & control
• File Transfer Protocol (FTP)
• Trivial File Transfer Protocol (TFTP)
• Hypertext Transfer Protocol
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Cisco 2 - Routers
Chapter 10
TCP/IP and Application Layer
Troubleshooting protocols:
• Telnet
• Packet Internet Groper (ping) – uses ICMP
• traceroute
Windows based utilities:
• NBSTAT – trouble shoot NetBIOS
• NETSTAT – provides TCP/IP statistics
• ipconfig/winipcfg
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Cisco 2 - Routers
Chapter 10
TCP Protocol
TCP (Transmission Control Protocol):
• layer 4
• reliable
• connection-oriented
• uses
• windowing
• synchronization
• sequence numbers
• acknowledgements
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Cisco 2 - Routers
Chapter 10
TCP Protocol
Transport layer (layer 4) enables a user’s device to segment data from
several upper-layer applications for placement on the same Layer 4 data
stream & enables a receiving device to reassemble the upper-layer
application segments.
This is a logical connection, sometimes called an end-to-end service.
The transport layer provides two (2) protocols:
• TCP
Which is connection-oriented, reliable providing flow control by sliding
window & sequence numbers
• UDP
Which is connectionless & unreliable. It’s advantage is speed. Depends
on upper layers for reliability.
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Cisco 2 - Routers
Chapter 10
Three-Way Handshake
A three-way handshake/open connection sequence synchronizes a
connection at both ends before the transferred data reaches the ends. The
exchange of introductory sequence numbers, during the connection
sequence, ensures that any data that is lost, due to problems that may
occur later, can be recovered.
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Cisco 2 - Routers
Chapter 10
Denial-of-Service - DoS
Denial-of-service (Dos) attacks are designed to deny services to legitimate
hosts attempting to establish connections. One type of DoS is known as
SYN flooding which occurs during the three-way handshake
synchronization process utilized by TCP.
The hacker initiates a synchronization but falsifies the source IP address.
This causes the attacked device to use up system resources such as
memory and processing time.
One way to defend against this type of DoS is to decrease the connection
timeout period and increase the connection queue size.
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Cisco 2 - Routers
Simple Acknowledgment
Chapter 10
Window size determines the amount of data that can be transmitted at one
time before receiving an acknowledgement. After a host transmits the
window-sized number of bytes, it must receive an acknowledgement
before it can send any more messages. For example, with a window size
of 1, each individual segment must be acknowledged before the next
segment can be transmitted. This results in inefficient use of bandwidth
by the hosts.
Simple
Acknowledgement
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Sliding
Window
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Cisco 2 - Routers
Sequence and Acknowledgment Numbers
Chapter 10
TCP provides sequencing of segments with a forward reference
acknowledgment. Each datagram is numbered before transmission. At the
receiving station, TCP reassembles the segment into a complete message.
If a sequence number is missing in the series, that segment is retransmitted. Segments that are not acknowledged within a given time
period result in re-transmission.
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Cisco 2 - Routers
Chapter 10
TCP/UDP Protocol
Both TCP & UDP uses IP as their underlying layer 3 protocol.
TCP provides services to:
• FTP
• HTTP
• SMTP
• DNS
UDP provides services to:
• DNS
• TFTP
• SNMP
• DHCP
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Cisco 2 - Routers
Port Numbers
Chapter 10
• Both TCP and UDP use port (or socket) numbers to pass information to
the upper layers. Port numbers are used to keep track of different
conversations that cross the network at the same time.
• Conversations, that do not involve applications with well-known port
numbers, are assigned port numbers that have been randomly selected
from within a specific range.
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Cisco 2 - Routers
Chapter 10
Ports Numbers
Ports numbers have the following assigned ranges:
• numbers below 255 are for public applications
• numbers from 255 to 1023 are assigned to companies for
marketable applications
• number above 1023 are unregulated
Port numbers are located at the transport layer and are serviced by the
network layer.
The network layer assigns the logical address or IP. It is then serviced
by the data link layer which assigns the physical or MAC address.
Ports in the header of TCP & UDP are called well-known or dynamic.
The order of encapsulation is port number, IP address, MAC.
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Chapter 10
ARP
ARP operates at the Internet layer of the TCP/IP layer.
Given an IP address, it will find the corresponding MAC address.
RARP – given MAC address, it will find the corresponding IP address.
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