Bus

• All transmissions travel full length of the cable and receive by all other stations
• Single point of failure n the cable
• If one of the links between any of the computers is broken, the network is down
• Primarily Ethernet
• These networks were originally designed to work with more sporadic traffic

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Ring

• Unidirectional transmission links form closed loop
• Token Ring and FDDI
• Similar to the Star topology, however there’s a device called a Multistation Access Unit (MAU)
• MAU works the same as a hub, but with Token Ring networks instead of Ethernet networks
• These networks were originally designed to serve large, bandwidth-intensive applications

Star

• Nodes connected to a central LAN or a junction box called a hub or a concentrator at the center of the network
• Provides reliability and often used by Bus and ring topology as the physical connection

Tree – branches can have multiple nodes

Mesh – all nodes are connected to every other node

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Packet Filtering Firewall – First Generation

• Screening router
• Operates at Network and Transport Level
• Examines Source and Destination IP address
• Can deny based on ACLs
• Can specify port

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Planning to take the CISSP Exam? Get a copy of my personal notes (300plus pages worth) that I used to pass the exam for only $25.00. Click the Add To Cart Button to Purchase Plus you will also get copies of notes from other CISSPs. Learn more about this package by visiting this blog entry: CISSP REVIEW NOTES I USED TO PASS THE EXAM. CLICK BELOW TO MAKE YOUR PURCHASE NOW. All Purchases are securely processed through Paypal. Once you click the button please check your shopping cart at the upper right hand side of the page to complete your order. IMPORTANT NOTICE: I MANUALLY REVIEW ALL ORDERS. SO ONCE YOU PURCHASE THE PRODUCT, THERE WILL BE SOME DELAY ON YOU RECEIVING AN E-MAIL FROM ME WITH THE LINK TO THE DOWNLOAD AREA OF THE PRODUCT. YOU WILL GET A RESPONSE FROM ME WITHIN 24-48 HOURS.

Application Level Firewall – Second Generation

• Proxy server
• Copies each packet from one network to the other
• Masks the origin of the data
• Operates at layer 7 (application Layer)
• Reduces network performance since it has to analyze each packet and decide what to do with it
• Also called Application Layer Gateway

Stateful Inspection Firewalls – Third Generation

• Packets analyzed at all OSI Layers
• Queued at the network level
• Faster than the Application Layer Gateway

Dynamic Packet Filtering Firewalls- Fourth Generation

• Allows modification of security rules
• Mostly used for UDP
• Remembers all of the UDP packets that have crossed the network’s perimeter, and it decides whether to enable packets to pass through the firewall

Kernel Proxy – Fifth Generation

• Runs on NT Kernel
• Uses dynamic and custom TCP/IP-based stacks to inspect the network packets and to enforce security policies

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TCP – Transmission Control Protocol

• Connection oriented
• Sequenced packets
• Acknowledgement is sent back for received packets
• If no acknowledgement then packet is resent
• Packets are re-sequenced
• Manageable data flow is maintained

Note: TCP and UDP use dynamic port numbers greater than 1023

UDP

• Best effort
• Doesn’t care about sequence order
• Connectionless
• Less overhead and faster than TCP

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Internet Layer Protocols

IP – Internet Protocol

• All hosts on a network have an IP address
• Each data packet is assigned the IP address of the sender and the receiver
• It provides an “unreliable datagram” services
• Provides:
  • No guarantees that the packet will be delivered
  • No guarantee that the packet will be delivered only once
  • No guarantee that it will be delivered in the order in which it was sent

ARP – Address Resolution Protocol

• Use the IP Address to get the MAC address
• MAC Address is 48 bit
• IP address is 32 bit
• Only broadcast to network first time, otherwise stores IP and MAC info in table

RARP – Reverse Address Resolution Protocol

• Use the MAC address to get the IP address
• RARP Server tells diskless machines’ IP address

ICMP – Internet Control Message Protocol

• Management Protocol and messaging service provider for IP
• Sends messages between network devices regarding the health of the network
• Ping is ICMP packet
• Ping checks if a host is up and operational

Note: TCP/IP does not define physical standards it uses existing ones

Other TCP/IP Protocols

Telnet

• Terminal Emulation
• No File Transfer

FTP

• File Transfer Protocol
• Can not execute files

TFTP

• Trivial FTP
• No directory browsing capabilities, no authentication
• Can only send and receive files
• UDP-base file transfer program that provides no security

NFS – Network File Sharing

SMTP – Delivers e-mails

X-Windows – For writing graphical interface applications

SNMP

• Simple Network Management Protocol
• Provides for the collection of network information by polling the devices on the network from a management station
• Sends SNMP traps (notification) to  MIBS – Management Information Bases

Bootstrap Protocol (BootP)

• Diskless bootup
• BootP server hears the request and looks up the client’s MAC address in its BootP file
• Internet Layer Protocol

Layered architecture

• Shows how communication should take place
• Clarify the general functions of a communication process
• To break down complex networking processes into more manageable sub-layers
• Using industry standard interfaces enables interoperability
• To change the features of one layer without changing the code in every layer
• Easier troubleshooting

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Open Systems Interconnect (OSI) Model

Layer 7 – Application

• Responsible for all application-to-application communications
• User information maintained at this layer is user data
• Security: Confidentiality, Authentication, Data Integrity, Non-repudiation
• Technology: Gateways
• Protocols: FTP, SMB, Telnet, TFTP, SMTP, HTTP, NNTP, CDP, GOPHER, SNMP, NDS, AFP, SAP, NCP, SET

Layer 6 – Presentation

• Responsible for the formatting of the data so that it is suitable for presentation
• Responsible for character conversion (ASCII/EBCDIC)
• Encryption/Decryption, Compressions and Virtual Terminal Emulation
• User information maintained at this layer is called messages
• Security: Confidentiality, Authentication, Encryption
• Technology: Gateway
• Protocols: ASCII, EBCDIC, Postscript, JPEG, MPEG, GIF

Layer 5 – Session

• Responsible for the setup of the links, maintaining of the link and the link tear-down between applications
• Security: None
• Technology: Gateway
• Protocols: Remote Procedure Calls (RPC), SQL, RADIUS, DNS, ASP

Layer 4 – Transport

• Responsible for the guaranteed delivery of user information
• Also responsible for error detection, correction and flow control
• User information at this layer is called datagram
• Security: Confidentiality, Authentication, Integrity
• Technology: Gateway
• Protocols: TCP, UDP, SSL, SSH-2, SPX, NetBIOS, ATP

Layer 3 – Network

• Responsible for the routing of user data from one node to another through the network including the path selection
• Logical addresses are used at this layer
• User information maintained at this layer is called packets
• Security: Confidentiality, Authentication, Data Integrity
• Technology: Virtual Circuits (ATM), routers
• Protocols: IP, IPX, ICMP, OSPF, IGRP, EIGRP, RIP, BOOTP, DHCP, ISIS, ZIP, DDP, X.25

Layer 2 – Data Link

• Responsible for the physical addressing of the network via MAC addresses
• There are two sublevels: MAC & LLC
• Has error detection, frame ordering and flow control
• User information maintained at this layer is called frames
• Security: Confidentiality
• Technology: Bridges, switches
• Protocols: L2F, PPTP, L2TP, PPP, SLIP, ARP, RARP, SLARP, IARP, SNAP, BAP, CHAP, LCP, LZS, MLP, Frame Relay, Annex A, Annex D, HDLC, BPDU, LAPD, ISL, ,MAC, Ethernet, Token Ring, FDDI

Layer 1 – Physical

• Responsible for the physical transmission of the binary digits through the physical medium
• Includes things such as the physical cables, interfaces and data rate specifications
• User information maintained at this layer is called bits
• Security: Confidentiality
• Technology: ISDN, Hubs, Repeaters, Cables