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Basics



VPN



SSH




SSL




Stunnel



VPN Vs SSH


VPN connects you to a network and SSH to a single computer.
SSH is application specific while a VPN encrypts all traffic on your computer.

VPN

Pros: Can use UDP or TCP, can disguise traffic 
Cons: no unified standard 
Uses: Remote access to company resources, providing security

SSH

Pros: doesn’t encrypt all your traffic, cheaper to run, single standardized & unified protocol 
Cons: Harder to set up, can only use TCP, doesn’t encrypt all your traffic, hard to disguise traffic, DNS leaks 
Uses: remote access to a single computer, providing security




SSH Vs SSL







NAT Vs PAT


Static NAT (Network Address Translation) - Static NAT (Network Address Translation) is one-to-one mapping of a private IP address to a public IP address. Static NAT (Network Address Translation) is useful when a network device inside a private network needs to be accessible from internet.



Dynamic NAT (Network Address Translation) - Dynamic NAT can be defined as mapping of a private IP address to a public IP address from a group of public IP addresses called as NAT pool. Dynamic NAT establishes a one-to-one mapping between a private IP address to a public IP address. Here the public IP address is taken from the pool of IP addresses configured on the end NAT router. The public to private mapping may vary based on the available public IP address in NAT pool.


PAT (Port Address Translation) - Port Address Translation (PAT) is another type of dynamic NAT which can map multiple private IP addresses to a single public IP address by using a technology known as Port Address Translation.

Here when a client from inside network communicate to a host in the internet, the router changes the source port (TCP or UDP) number with another port number. These port mappings are kept in a table. When the router receive from internet, it will refer the table which keep the port mappings and forward the data packet to the original sender.












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