The OSI Model Demystified
The OSI Model
Layer 7 -- Application Layer -- The layer users interact with
Layer 6 -- Presentation Layer -- Generally the layer the Operating System is on
Layer 5 -- Session Layer -- The layer that controls the communication session between two computers
Layer 4 -- Transport Layer -- The layer that controls Windowing and other tasks related to communication
Layer 3 -- Network Layer -- The layer that Routers and IP addresses operate at
Layer 2 -- Data Link Layer -- The layer that Switches, MAC Addresses and ARP reside at
Layer 1 -- Physical Layer -- The layer that cabling resides on
TCP/IP and Subnetting
TCP/IP Overview (2:32)
How TCP/IP Works (16:53)
TCP/IP Numbering (43:00)
Subnet Masking (48:17)
Final Thoughts (64:03)
Is technically a Protcol Suite
IP Routes Traffic
Layer 3 OSI Model Network
Routable Networks (sub networks)
TCP controls transmission between connected systems
Layer 4 OSI Model Transport
Windowing is the process of sending data from one computer to another in TCP/IP version 4
2. How TCP/IP Works
IP Addresses -- Every device on a TCP/IP network needs an individual IP Address
DNS (Domain Name Service/Server) resolves Domain names into IP Addreses
DHCP (Dynamic Host Control Protcol) Servers automatically assign IP information to clients for a specific time period (Lease). Clients try to renew leases at 50% expiration point.
Default Gateway (Router) connects networks. If an IP Address cannot be found on the local network the computer tries to use the Default Gateway to find the target.
Subnets and Subnet Masking -- Subnets are individual networks. Subnet Masks divide IP Addresses in Subnet Number and Host Number
What the Number Mean
IP Addresses and Subnet Masks are made of 4 Octets of Bits
IP Addresses contain the Subnet Number and Host Number. The Subnet Mask tells you where the subnet number ends and the host number begins.
Classful Networks A, B, C,D,E Gone now use CIDR
The Highest Address in a Subnet Range is the Broadcast address
To determine the number of subnets (n is the number of bits used)= 2n
To determine number of Hosts = 2n -2
This class teaches students how use DNS to redirect computer or network users to alternate websites or servers for security or malicious purposes.
How DNS Works
Editing the HOSTS file
Alternate Public DNS
Planning a DNS Hack
Reasons to Hack DNS
DNS resolves Domain Names to IP Addresses
Warning: Use at your own risk
HOSTS file is the local file that resolves Domain Names
Windows Location = C:\Windows\System32\drivers\etc
Example = 10.1.10.2 www.elithecomputerguy.com
In Vista/ Windows 7 First Open Notepad using "Run as Administrator" and then open the HOSTS file. Otherwise you will not be able to save your edits.
Computers FIRST try to Resolve a Domain Name with the HOSTS file, they then Go To the LOCAL DNS Server, and then they Query the PUBLIC DNS Server. If any server has a record the computer does not ask any other sources. SO if the HOSTS file has a record the computer uses that record and stops.
Using Alternate DNS
You do not have to use the Public DNS IP Addresses that your ISP gave you. You can use Alternate Public DNS Servers.
The benefit of using a server like OpenDNS.org is that they will prevent Domain Names for malicious websites from resolving. This is a HUGE security tool.
You can create your own Public DNS Server for Good/ Bad Purposes.
The DNS Attack
HOSTS file can be compromised either through manual editing, or through scripting. If users are logged in as USERS vs. ADMINISTRATORS there is far less chance that a script will be able to modify the HOSTS file.
By Wardriving or Plugging Into an Unsecured Network Jack You May be able to Hack the DNS Server. Routers/ Modems with default passwords are easy to Hack.
A clever, well disguised DNS Hack is very difficult to detect once it has been successfully implemented, and it is moderately difficult to circumvent if it is done by a network administrator to secure a network.
Hacking DNS is the EASIEST way to either protect or attack a network or computer