Network Address Translation

PREROUTING

Address translation occurs before routing.

Facilitates the transformation of the destination IP address to be compatible with the firewall’s routing table.
Used with NAT of the destination IP address, also known as destination NAT or DNAT.

POSTROUTING

Address translation occurs after routing.

This implies that there was no need to modify the destination IP address of the packet as in pre-routing. Used with NAT of the source IP address using either one-to-one or many-to-oneNAT. This is known as source NAT, or SNAT.

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