Related: L3 Network
NAT is a crutch that was designed to overcome IPv4 shortages, and consequentially provides some security. Does not needed for IPv6.
Translates Private IP Address into Public
Static NAT
1 private to 1 public (AWS IGW), used for IP consistency. Has NAT table.
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Dynamic NAT
1 private to 1st available public from the pool. Temporary allocations.
Multiple devices can use same IP if they do it in different time.
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Port Address Translation (PAT)
Many private addresses to 1 public (VPC NATGW).
Uses rewrites source port to random source port and keeps relations with NAT table, then sends this packet to destination. Destination responds to source port and source IP, router or NATGW receives IP packet and replaces source port and IP with origin source port from the NAT table.
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