Transcript Document
Computer Security Workshops Networking 101 Reasons To Know Networking In Regard to Computer Security To understand the flow of information on the Internet To understand the levels of activity in network traffic flow To understand the basis for vulnerabilities To understand the basis for security tools and how they work Base Principle – Packet Switching Messages broken up into packets Packets are sent onto network, routed to destination, reassembled Advantages (compared to circuit switching; e.g. traditional phones) Better sharing of bandwidth Greater overall efficiency Allows more users, no greater delay Protocol Layering Protocol: a convention for communication between two agents (aka handshaking) Motivation: Separation of functionality Layers take care of particular task re: information Offer services to next layer in protocol stack Advantage: modularity Disadvantages: possible overlap, redundancy of functionality Protocol Data Units Layer sends message by building a protocol data unit (PDU) Take data from layer N, add additional information to meet needs of layer N-1 PDU handed to next lower layer Lower layer now has responsibility for message Internet Protocol Stack Seven layers in Open Systems Interconnect (OSI) model 7) Application 6) Presentation 5) Session 4) Transport 3) Network 2) Data Link 1) Physical General Layer Functions Segmentation / Reassembly Breaking large message into standard size chunks Error Control How to detect or correct errors Flow Control Avoid overwhelming slower systems Multiplexing Sharing of lower-level connections Connection setup How to establish a virtual communication path Application Layer (7) Function: High-Level Application Systems and End-User Processes Implemented in: Software PDU: Message Examples ftp, http, smtp, telnet, … Presentation Layer (6) Function: Provides independence from differences in data representation by formatting and encrypting data Implemented in Software Examples: ASCII encoding, NFS, FTP file path/name translation Session Layer (5) Function: Establishes, manages and terminates connections between applications Implemented in software Examples: SSL, DNS, RPC Transport Layer (4) Function/Service: Transport message from one system to another system Implemented in: Software PDU: Segment Two methods TCP (connection-oriented protocol) UDP (connectionless protocol) TCP TCP=Transmission Control Protocol Connection-Oriented Service Guaranteed Delivery of Message Flow Control Breaks message into shorter segments Advantage: More Control Examples http, ftp, smtp, telnet UDP UDP = User Datagram Protocol Connection-less Service No Guaranteed Delivery of Message No Flow Control / Handshaking No Overhead For Connection Continuous Data Stream Advantage: Faster Disadvantage: Possible loss of information Examples Video, Voice (e.g. phone) Network Layer (3) Function/Service: Routing segments from host to host, through intermediate systems Network Layer receives segment and destination address from Transport Layer Implemented in: Hardware & Software PDU: Datagram Two major parts IP Protocol: structure of datagram, how end systems (and routers) act on this information Routing protocols: for transfer from source host to destination host Examples: IP, IPX Data Link Layer (2) Function/Service: Move a datagram from one node to the next in the route Implemented in: Hardware PDU: Frame Examples: Ethernet, Token Ring, FDDI, Gigabit Ethernet Physical Layer (1) Function/Service: Routing physical bits from one network node to adjacent node Implemented in: Hardware PDU: Bits Examples Optical fiber, Twisted pair wire, Coaxial cable Voltage levels, signaling Types of Hardware/Software Systems End Systems / Hosts Implement all layers Routers/Packet Switches Implement layers 1-3 Can implement IP protocol Bridges Implement layer 1-2 Hubs Implement layer 1 only Essentially repeaters Firewalls Packet filtering (operate at layer 3) Application gateways (operate at layer 7) Internet Addressing 32-bit quantity that uniquely identifies internet host Displayed www.xxx.yyy.zzz Split into two parts: network and host E.g. 198.23.168 network (198.23.168.0/24) has 256 possible hosts (last part 0-255) Certain network segments reserved Can be used for isolated private networks 10.0.0.0 – 10.255.255.255; 172.16.0.0 – 172.31.255.255; 192.168.0.0 – 192.168.255.255 Port Certain system process must respond to a particular application protocol (e.g. ftp, smtp) Port is the “address” for application communication on system E.g. Port 80 for http E.g. Port 25 for smtp E.g. Port 1521 for Oracle connections Port List: http://www.iana.org/assignments/portnumbers Socket Interface between the application layer and the transport layer Acts as an API between application and network Programmer only controls application side, plus a few transport level details Transport protocol (TCP or UDP) A few transport parameters (e.g. maximum buffer size) Additional Information Internet Engineering Task Force (IETF) http://www.ietf.org Primary documents: RFCs IP: RFC 791 TCP: RFC 793 UDP: RFC 768 Internet Addressing: RFC 900 OSI Model and Information Security http://www.giac.org/practical/GSEC/Damon_R eed_GSEC.pdf