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 Better sharing of bandwidth Greater overall efficiency Greater overall efficiency Allows more users, no greater delay 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 Layers take care of particular task re: information Offer services to next layer in protocol stack Offer services to next layer in protocol stack Advantage: modularity Advantage: modularity Disadvantages: possible overlap, redundancy of functionality 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 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 7) Application 6) Presentation 6) Presentation 5) Session 5) Session 4) Transport 4) Transport 3) Network 3) Network 2) Data Link 2) Data Link 1) Physical 1) Physical

General Layer Functions Segmentation / Reassembly Breaking large message into standard size chunks Breaking large message into standard size chunks Error Control How to detect or correct errors How to detect or correct errors Flow Control Avoid overwhelming slower systems Avoid overwhelming slower systemsMultiplexing Sharing of lower-level connections Sharing of lower-level connections Connection setup How to establish a virtual communication path 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, … 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) TCP (connection-oriented protocol) UDP (connectionless protocol) UDP (connectionless protocol)

TCP TCP=Transmission Control Protocol Connection-Oriented Service Guaranteed Delivery of Message Guaranteed Delivery of Message Flow Control Flow Control Breaks message into shorter segments Advantage: More Control Examples http, ftp, smtp, telnet http, ftp, smtp, telnet

UDP UDP = User Datagram Protocol Connection-less Service No Guaranteed Delivery of Message No Guaranteed Delivery of Message No Flow Control / Handshaking No Flow Control / Handshaking No Overhead For Connection No Overhead For Connection Continuous Data Stream Advantage: Faster Disadvantage: Possible loss of information Examples Video, Voice (e.g. phone) 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 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 IP Protocol: structure of datagram, how end systems (and routers) act on this information Routing protocols: for transfer from source host to destination host 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 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 Optical fiber, Twisted pair wire, Coaxial cable Voltage levels, signaling Voltage levels, signaling

Types of Hardware/Software Systems End Systems / Hosts Implement all layers Implement all layers Routers/Packet Switches Implement layers 1-3 Implement layers 1-3 Can implement IP protocol Can implement IP protocolBridges Implement layer 1-2 Implement layer 1-2Hubs Implement layer 1 only Implement layer 1 only Essentially repeaters Essentially repeatersFirewalls Packet filtering (operate at layer 3) Packet filtering (operate at layer 3) Application gateways (operate at layer 7) Application gateways (operate at layer 7)

Internet Addressing 32-bit quantity that uniquely identifies internet host Displayed Split into two parts: network and host E.g network ( /24) has 256 possible hosts (last part 0-255) E.g network ( /24) has 256 possible hosts (last part 0-255) Certain network segments reserved Can be used for isolated private networks Can be used for isolated private networks – ; – ; – – ; – ; –

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 80 for http E.g. Port 25 for smtp E.g. Port 25 for smtp E.g. Port 1521 for Oracle connections E.g. Port 1521 for Oracle connections Port List: numbers numbershttp:// numbers

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) Transport protocol (TCP or UDP) A few transport parameters (e.g. maximum buffer size) A few transport parameters (e.g. maximum buffer size)

Additional Information Internet Engineering Task Force (IETF) Primary documents: RFCs Primary documents: RFCs IP: RFC 791 TCP: RFC 793 UDP: RFC 768 Internet Addressing: RFC 900 OSI Model and Information Security eed_GSEC.pdf eed_GSEC.pdf eed_GSEC.pdf eed_GSEC.pdf