CSC414 Communication Models Computer Network Client/Server Model System - Server Program Fundamentals Addressing - Runs on computer that has files to be shared - Web Server, Mail Server, Warcraft Server Server Client - Client Program Apache Firefox - Computer that needs to access remote files - Web Browser, Mail Client, World of Warcraft Digital Forensics Center Department of Computer Science and Statics THINK BIG WE DO Peer to Peer Model - Single program

U R I - makes files on computer available Peer Peer http://www.forensics.cs.uri.edu - accesses remote files LimeWire LimeWire

Addressing Data Domain Names

http://www.uri.edu:80/courses/cs/index.html Hierarchical system for name creation and registration protocol computer directory file - Created so users would not have to memorize IP addresses

address port - Global domain name system provides global scope for user friendly addresses OSI Model Domain Name Application Layer Country Codes Country Domain Type Common .us United States .biz Business File requested by client Presentation Layer Top Level .uk United Kingdom .com Commercial .au Australia .edu US Educational Folder or directory path on server Session Layer Maps to special directory used by Port Domains .cn China .gov US Government application .mil Military Transport Layer .ca Canada Mailbox on the machine the .de Germany .net Network server or peer is checking Top level Network Layer .org Nonprofit Organization IP Address (Logical) domains are .ru Russia What machine has the shared data .info Info Domain approved by .in India Where to send the shared data MAC Address (Physical) Data Link Layer .name Personal Name ICANN .jp Japan Data request formats and commands .tv Television (Tuvalu) .eu European Union How the data is formatted when sent Physical Layer Physical Connection .xxx Pornography

Domain Names Domain Names

Domain Name System (DNS) Domain Name System (DNS) www.cs.uri.edu

Client Computer - Translates domain names into IP addresses Root Server Client Application

- A massive distributed database containing a directory of servers Query to DNS Client - Each entry contains a domain name and an associated IP address DNS Client App Top Level Domain Server Ask for .edu TLS (for .edu) - Root Servers Local DNS Server Query to Local Domain Found Name Server (ISP) Local DNS ANS Return the address of TLS - Have all Top Level Domain (TLD) addresses Table uri.edu Check local DNS table uri.edu www.cs.uri.edu Ask for - Top Level Domain Servers (TLS) Not Found - Check Root Server Return the address of the Then Check Top Level Domain Server - Maintain local domain addresses Authoritative Server for Host Domain Ask for cs.uri.edu ANS - Authoritative Domain Servers Then Check Authoritative Server Authoritative Server (for uri.edu) Subdomain Top Level Domain - Maintain information on sub-domains Return IP Address of cs.uri.edu Return IP Address of cs.uri.edu - Often at an ISP or Intranet site to Client IP Addresses IP Addresses

Logical addresses - IPv6 Assigned in blocks of IP Block Addresses contiguous addresses - IPv4 - Replaces IPv4 to provide additional IP 202.66.31.128 - Organization Address addresses (soon) 11001010 01000010 0011111 10001010 - 32-bit addresses arranged as 4 integers, - Number of addresses is a power 202.66.31.138 - One Local Host on Network delimited by dots - 128-bit addresses arranged as 8 groups of two of four-digit hexadecimal numbers - Each integer is between 0 and 255 separated by colons Divided into three levels 255.255.255.128 - Subnet Mask 11111111 11111111 11111111 10000000 - Example: - Leading zeros and zero values in one or - Network address more consecutive groups may be - 208.80.152.2 eliminated - Subnetworks (subnets) Reserved IP Addresses - (Private) - Wikipedia’s IP address - Example: - Hosts (nodes) Address Range Total Number of Addresses 10.0.0.0 - 224 or ! 16 million - World has officially run out of IPv4 6E:2A20:::35C:66C0::5500 10.255.255.255 006E:2A20:0000:0000:035C:66C0:0000:5500 addresses! Masks 172.16.0.0 - 220 or ! 1 million 172.31.255.255 - Used to separate the different 192.168.0.0 - 216 or ! 64,000 parts of the address 192.168.255.266

IP Addresses Assigning IP Addresses

Assigned in blocks of 192.168.0.12 Dynamic Host Configuration Protocol (DHCP) Manually Assigned Address contiguous addresses - Bank of available IP addresses maintained - Entered manually by system Wireless Ethernet 192.168.0.101 192.168.0.2 administrator - Number of addresses is a power - Assigned dynamically to computers when the of two computers are attached to the network - Must also manually enter subnet mask, IP address of router or 192.168.0.50 - Used by large organizations and broadband Divided into three levels gateway and DNS server providers - Network address 202.66.31.138 - DHCP client on device broadcasts query to - Guarantees device has same address each boot - Subnetworks (subnets) 192.168.0.53 locate the DHCP server WiredEthernet - Good for any kind of server - Hosts (nodes) - DHCP server responds with lease that BootP Protocol 192.168.0.54 includes: Masks To WAN or - an IP address, domain name of network, IP - For devices that boot from a - Used to separate the different address of DNS server, subnet mask, IP address network disk parts of the address of gateway and other configuration parameters

Resolving IP Addresses

Address Resolution Protocol (ARP) MAC (medium-access control) address - Implemented at the network layer - Most common type of physical address - Translation of IP address to physical - Every manufactured device that may address at each intermediate node until connect to a network anywhere in the destination is reached world is supplied with a permanent, unique MAC address Network Addressing - Broadcast of the IP address is sent to every node on the network. - Format consists of 48 bits arranged as 6 two-digit hexadecimal numbers separated - Matching node responds with a physical address by colons - Example: 00:C0:9F:6C:F9:D0 Digital Forensics Center - Physical address (MAC address in the case of THINK BIG WE DO Ethernet) is sent in frame to the data link layer Department of Computer Science and Statics - At final destination, packet is passed up to the transport layer for deployment to the application layer U R I http://www.forensics.cs.uri.edu