INTRODUCTION TO NETWORKS8/2/2015

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

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 – email• 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. 192.168.1.1

Private Addresses

• 10.0.0.1 – 10.255.255.254 (10.0.0.0/8)• 172.16.0.1 – 172.31.255.254 (172.16.0.0/12)• 192.168.0.1 – 192.168.255.254 (192.168.0.0/16)

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: www.smu.edu resolves to 129.119.70.166

• 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 http://www.freeantennas.com/projects/template2/• 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?