The IT Stuff

The Internet Protocol Suite (commonly known as TCP/IP) is the set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were the first two networking protocols defined in this standard.
The [...]

Internet Protocol security (IPSec) is a framework of open standards for helping to ensure private, secure communications over Internet Protocol (IP) networks through the use of cryptographic security services.
It is a suite of protocols for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a data stream. IPsec also includes protocols [...]

The Transmission Control Protocol (TCP) level of the TCP/IP transport protocol is connection-oriented that is it  means that, before any data can be transmitted, a reliable connection must be obtained and acknowledged.
There are two scenarios where a three-way handshake will take place:

Establishing a connection (an active open)
Terminating a connection (an active close)

SNMP is an application-layer protocol that provides a message format for communication between managers and agents.
The SNMP system consists of an SNMP manager, an SNMP agent, and a MIB.
The SNMP manager can be part of a network management system (NMS). The agent and MIB reside on the switch/router etc.
The SNMP agent contains MIB variables whose [...]

NAT can take a single IP address and distribute it for use of many users by creating a Local Area Network (LAN).The LAN will share a single globally recognized IP address.
Disadvantages:

Translation sometime complex (e.g. FTP, VOIP).
Apps using dynamic ports (UPnP).
Does not scale (today avg. of 500 active sessions per user).
Introduce states inside the network:
Multi-homed networks
Breaks [...]