INTRODUCTION TO NETWORKS 8/2/2015 SSIG SOUTHERN METHODIST UNIVERSITY

OSI MODEL (5 LAYER) Layer 1: Physical – Cables and bits Layer 2: Data Link – MAC Layer 3: Network – IP Addressing/Routing Layer 4: Transport – Management/Sessions -> Packets Layer 5: Application – Allows programs to connect to network/Human interaction Unless you are a networking ninja, you have probably only done stuff at Layer 5 or Layer 3 if you set up your home LAN.

LAYER 1: PHYSICAL LAYER Physical cables/bits Electrical impulses Conversion between data -> signals Our data needs to be converted into electronic signals to send Includes: Pinouts – cable/connector pinouts Voltages – voltages across cables Cable specifications – CAT5/CAT6/Coaxial/Fiber NICs – Network Interface Card Etc.

LAYER 2: DATA LINK LAYER Access to a computer or device Package the physical bits/impulses into data and frames Frames: segments of data being pushed over layer 2 connectivity Transfer from point -> point MAC Address – Media Access Control – Unique to NIC Truck driver handing off the box to house.

LAYER 3: NETWORK LAYER - PACKETS “IP” Layer – This is where we use IP addresses Not hard coded to a NIC. IP addresses are logical addresses. Functional means of transferring data through one -> more networks Translate logical addresses to Physical Performs: Network Routing Fragmentation/Reassembly Packets Wait we already have a MAC, why do we need a IP? IPv6 Kind of infeasible because of the way we currently have networks set up.

LAYER 4: TRANSPORT LAYER Management / Control Transfer of Data Split communications into packages Can’t just send all our data in one packet. Size limits. Types: TCP – receipt (verification of delivery) – retransmission if failure – Banking UDP – no verify (no verification of delivery) – stream of packets – Skype/VoIP HTTP, HTTPS, SSH, SSL/TLS – All TCP or UDP based.

TCP Transmission Control Protocol Connection Oriented – Delivery confirmation Larger Packet Size Packets are numbered. Therefore they can be ordered. Allows for retransmission 1 -> 1 connection Three way handshake SYN -> <- SYN/ACK ACK -> Data is a stream – “TCP Stream” – Wireshark

UDP User Datagram Protocol Small packet sizes Streaming. Faster because no ACK Connectionless No error recovery Can be broadcast

LAYER 5: APPLICATION LAYER Network Access Enables apps/software to access the network Identify communication partners Determine resources available Sync communications Browsers Includes: SMTP – HTTP – webpages/Internet FTP – File Transfer Protocol

NETWORK DEVICES/COMPONENTS Hub – “Dumb” – not really used anymore. Switch – Control the flow of network traffic Router – Connected to at least 2 networks. Forwards data packets along networks. Proxies – Forward and Reverse. Content Filtering/Monitoring Firewalls DMZs

FIREWALLS – “FIRST LINE OF DEFENSE” Firewalls – software or hardware implementations on the network to filter network traffic. Incoming and Outgoing traffic Can configure and set rules to detect traffic allowed into/out of the network Types of firewalls: Packet inspection – inspect every packet Application filtering – prevent traffic from calling upon certain applications Stateful Firewalls – State table for outgoing traffic. Can block by IP address or port address DMZ construction – Firewalls back to back Web servers Guest networks

NETWORK ADDRESSING – IP ADDRESSING IP Addresses are 4 bytes – 32 bits Broken into 4 octets Ex Private Addresses – ( /8) – ( /12) – ( /16) Subnet Mask – used to determine which subnet an IP address belongs to Allows to separate/determine the IP address’s two components Network Address Host Address

NAT – NETWORK ADDRESS TRANSLATION NAT is a way to map an entire network (or networks) to a single IP address When the number of IP addresses assigned by ISP is less than number of hosts on your network – you need NAT Enables the LAN to use one set of IP addresses for internal traffic and a second for external traffic Handled by the router Type of firewall by hiding internal IP addresses

DNS – DOMAIN NAME SYSTEM Hierarchical distributed naming system for computers, services, or any resource connected to the Internet or private network. Internet’s primary directory service Translates human-readable computer hostnames Example: resolves to www.smu.edu Try it, it works.

WIRELESS NETWORKS – WIFI (802.11) Wireless Routers Gateways/Modems Access Points Repeaters – Capture root signal and rebroadcast – Roaming Possible Throughput – Mbps Signal strength – 2.4GHz / 5GHz Which should you use?

WIRELESS NETWORKS CONTINUED Directional Antennas vs Omnidirectional How to maximize your signal range? Parabolas Place in a high location Check what channel your router is on WiFi Analyzing apps on your Phone are fun QoS and Prioritization WPS – WiFi Protected setup – can be exploited WPA2 - Never use WEP

QUESTIONS?