networking_refresher.ppt
TRANSCRIPT
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“Almost” everything you need to know about networking!
Mahdi Nasereddin
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Before we start
Information Security Development Conference 2006David Rowan, Senior Vice President and Director of
Enterprise Technology Risk Management, Sun Trust Banks, Inc.
• “Policy is Corporate Law” – reviewed by 75 people• HR Enforcement of Security Policy• “No Assumption of Privacy”• 50% of security problems are internal!!• Passwords
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Update on Information Security Development Conference 2006 (Cont.)David Rowan, Senior Vice President and Director of
Enterprise Technology Risk Management, Sun Trust Banks, Inc.
• Risk choices:– Accept it
– Mitigate it
– Insurance
– Avoid it
• “Certifications will get you interviewed,Character and skill will get you hiredLeadership will get you promoted”
• Phishing sites (7 sites/day, 2 hrs/site to bring it down)
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Update on Information Security Development Conference 2006 (Cont.)
PasswordsA lot of research in this area Interesting site (Passfaces)
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The Basics
Hub? Switches?
Collision Domains? Routers?
Broadcast Domains?
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Networking Basics
Internetworking ModelsThe OSI model
• IMPORTANT: Reference Model• “A Reference Model is a conceptual blueprint of how
communications should take place”• Created by ISO (International Organization for
Standardization) in the 1970s to allow computer systems made by different vendors to communicate with each other
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Open Systems Interconnection (OSI)
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical
• Provides user interface• Initiates services• Transfer data into standard format
before transmission
• Keeps data different applications’ data separate
• Control the data exchange
• Error Correction• Reliable or unreliable delivery
• Logical addressing for data packets
• Routing is performed in this layer
• Moves bits between devices• Specifies voltages, cables, and
cables
• NIC software function• How data in packaged• Error detection “Not Correction”
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Advantages of using the OSI model
Allows multiple-vendor development through standardization
Prevents changes in one layer from affecting other layers
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Data Encapsulation
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TCP/IP “DoD Model”
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Process/Application Layer Protocols
Telnet “Virtual terminal” File Transfer Protocol “FTP” Trivial File Transfer Protocol “TFTP” Network File System “NFS” Simple Mail Transfer Protocol “SMTP” Line Printer Daemon “LPD” X Windows Simple Network Management Protocol “SNMP” Domain Name Service “DNS” Dynamic Host Configuration Protocol “DHCP”
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The Transport Layer “Host to Host”
Layer 4 of the OSI model It segments and reassemble data into a data
stream Examples of transport layer protocols:
TCPUDP
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Transport Layer Concepts
Flow Control Data integrity is ensured by maintaining flow control Flow control prevents the sender from overflowing
the receiver. Flow control is established using
1. Connection oriented communication
2. Windowing
3. Acknowledgements
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Connection-Oriented Communication
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Please stop!! My buffer is full!!
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Windowing
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Transport Layer Protocols
Transmission Control Protocol “TCP”
ACK, SYN, RESET, PUSH, URG, and FIN “See Page 31”
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Transport Layer Protocols
User Datagram Protocol “UDP”
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TCP versus UDP
TCP UDP
Sequenced Not sequenced
Reliable Not reliable
Connection Oriented Connectionless
Virtual circuit Low overhead
Three-way handshake No acknowledgement
Windowing flow control No flow control
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Active participant(client)
Passive participant(server)
SYN, SequenceNum = x
SYN + ACK, SequenceNum = y,
ACK, Acknowledgment = y + 1
Acknowledgment = x + 1
3 way handshake
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Port Numbers
Used by TCP and UDP to communicate with upper layers keep track if different conversations crossing the network simultaneously
Sender port number start at 1024
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Port Numbers to remember
Port Application
21 ftp
23 telnet
53 DNS
69 TFTP
110 POP3
80 HTTP
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The Network Layer “Internet”
Layer 3 of the OSI model, which handles data routing and addressing.
The network layer keeps track of the network devices and determines the best way to move data.
It uses IP or IPX address
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IP Addressing
IP address x.x.x.x Net Mask
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The Network Layer
Routing Table Network Addresses Interface Metric
Packets used in the network layer Data packets
• Routed protocols (examples: IP and IPX)
Route updates• Routing protocols (examples: OSPF, and RIP)
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Routing
IP Routing is the process of moving packets from one network to another network.
To be able to route packets a router needs to know “at least” the following: Destination address Neighborhood routers Possible routes to all remote networks Best route to each remote network How to maintain and verify routing information
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Routing
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Static versus Dynamic Routing
Static routing: The administrator has to enter the routing table MANUALLY!
Dynamic routing: routers update each others routing tables automatically
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More About Routing
Routers by default will not forward any broadcast or multicast packets
Routers use the logical address in the network layer header to determine where to send the packet
Routers can use access lists
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Internet Layer Protocols
Internet Protocol “IP” Internet Control Message Protocol “ICMP” Address Resolution Protocol “ARP” Reverse Address Resolution Protocol “RARP” DHCP “Dynamic Host Configuration Protocol”
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Internet Protocol
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Protocol Numbers
Protocol Protocol Number
ICMP 1
IGRP 9
IPv6 41
GRE 47
TCP 6
UDP 17
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ARP
A machine has an IP but does not know the MAC Address
A table is maintained for IP to MAC translation A translation is removed after 15 minutes if no
update Broadcast is used
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DHCP
Automatically assigns IP addresses
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ICMP
Error reporting Examples
Host unreachable ICMP-Redirect
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The Data Link Layer “Network Access”
Layer 2 of the OSI model that is responsible for data transfer across a single physical connection (or series of bridged connections, between two Network entities).
It also handles error notification. It uses the hardware address
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Data Link Layers
The data link layer has 2 sublayers1. Media Access Control (MAC) 802.3:
– Defines how packets are placed on the media.
– Physical addressing is defined here.
2. Logical Link Control (LLC) 802.2:– This layer is responsible for identifying the network protocols,
and then encapsulating them
Switches are at the Data link layer. Why?
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The Physical Layer “Network Access”
Layer 1 of the OSI model which concerns the mechanical, electrical and functional aspects of connections in a communications medium.
Hubs are at the Physical layer.
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NAT and PAT?
Network Address Translation Port Address Translation