Transcript Module 10 - IIS Windows Server

CCNA 2 v3.1 Module 10
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Intermediate TCP/IP
CCNA 2
Module 10
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TCP/IP Operations
• IP addresses
Allow for the routing of packets between networks
Makes no guarantees about delivery
• Transport layer is responsible for
Reliable transport of data and regulation of data flow from
source to destination
This is accomplished using
sliding windows
sequencing numbers
a synchronization process that ensures each
host is ready and willing to communicate
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TCP/IP Segment Format
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Synchronisation – 3 way handshaking
•
Prior to data transmission the two
communicating hosts go through a
synchronization process to establish a virtual
connection
•
This synchronization process
Insures both sides are ready for data transmission
Allows the devices determine the initial sequence
numbers
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Synchronisation – 3 way handshaking
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Sequence Numbers
• Part of initiating communication between the two
devices
• Act as reference starting numbers between the
two devices
• Give each host a way to ACK the SYN so that the
receiver knows the sender is responding to the
proper connection request
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Denial Of Service Attacks
• Denial of service attacks (DoS)
• Designed to deny services to legitimate
hosts attempting to establish connections
• Common method that hackers utilize to
halt system response
• One type of DoS is known as SYN
flooding
Exploits the normal three-way handshake and
causes targeted devices to ACK to source
addresses that will not complete the
handshake
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SYN Flooding
In a DoS attack, the hacker
initiates a synchronization
but spoofs the source IP
address
To defend
against these
attacks,
system
administrators
may decrease
the connection
timeout period
and increase
the connection
queue size.
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Windowing and Window Size
Sliding window allows the destination device to indicate to
the source a need to decrease or increase the amount of
data being sent because it is incapable at that time of
dealing with that much data
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Sequencing numbers
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Positive Acknowledgment and Retransmission
(PAR)
•With PAR, source sends a
packet, starts a timer, and waits
for an ACK before sending the
next packet
•If timer expires before source
receives an ACK, the source
retransmits the packet and
restarts the timer
•TCP uses expectational
acknowledgments - ACK
number refers to the next octet
that is expected
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UDP operation
•Not all applications need to guarantee delivery of
the data packet
•They use UDP
a faster, connectionless delivery
Described in RFC 768
protocol that exchanges segments without
acknowledgments or guaranteed delivery
Does not use windowing
Does not use acknowledgments
Application layer protocols must provide error detection
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Overview of Transport Layer
Ports
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Multiple Conversations Between Hosts
A port number must be associated with the conversation
between hosts to ensure that the packet reaches the
appropriate service on the server
Without a way to distinguish between different conversations,
the client would be unable to send both an email and browse
a web page, using one server at the same time
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Ports for Services
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Ports for Services continued…
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Ports for Clients
•Destination ports - ports for services
Normally defined using the well-known ports
•Source ports
Set by the client are determined dynamically
Client determines the source port by randomly assigning a
number above 1023
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Port numbering & well-known port no’s
• Port numbers are represented by 2 bytes
in the header of a TCP or UDP segment
16-bit value - port numbers from 0 to 65535
• Port numbers are divided into 3 categories
1 to 1023 ports are well-known ports
1024 to 49151 are registered ports
49152 to 65535 are defined as dynamic or
private ports
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Multiple Sessions Between Hosts
• A pair of sockets, one on each host, forms a
unique connection.
For instance, a host might have a telnet connection,
port 23, while at the same time be surfing the net, port
80. The IP and the MAC addresses would be the same
because the packets are coming from the same host.
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Sockets
• Transport layer
Port numbers are located here
Serviced by the network layer
• The network layer
assigns the logical address (IP address)
is then serviced by the data link layer
• Data link layer
assigns the physical address (MAC address)
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