[Day 12] 3. NAT (Network Address Translation)

• Definition: NAT is the method where the source or destination IP address and/or port number of a packet is modified as it travels through a router or firewall.
• Purpose:
  • To hide internal private IP addresses behind a public IP.
  • To allow multiple devices to share a single public IP address for accessing the internet.
  • To redirect traffic for specific services.

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Types of NAT

SNAT vs. DNAT

1. Source NAT (SNAT):

   • Function: Modifies the source IP address in the packet.
   • Use Case: Common for outbound traffic from private networks to the internet.
   • Example: Changing a private IP (
     Copy

     192.168.1.10

     ) to a public IP (
     Copy

     203.0.113.1

     ).

2. Destination NAT (DNAT):

   • Function: Modifies the destination IP address in the packet.
   • Use Case: Redirects inbound traffic to specific servers within a private network.
   • Example: Redirecting traffic from a public IP (
     Copy

     203.0.113.1

     ) on port
     Copy

     80

     to a private IP (
     Copy

     192.168.1.20

     ).

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Static NAT vs. Dynamic NAT

• Static NAT:

  • Function: Maps a single private IP to a single public IP.
  • Characteristics: The mapping is constant.
  • Use Case: Hosting servers or services that need consistent access.
  • Example: Server (
    Copy

    192.168.1.10

    ) always mapped to public IP (
    Copy

    203.0.113.10

    ).

• Dynamic NAT:

  • Function: Maps multiple private IPs to a pool of public IPs.
  • Characteristics: The mapping is dynamic.
  • Use Case: Situations with limited public IP addresses.
  • Example: Devices (
    Copy

    192.168.1.10

    ,
    Copy

    192.168.1.11

    ) dynamically assigned public IPs (
    Copy

    203.0.113.10

    ,
    Copy

    203.0.113.11

    ).

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Clarifications

• SNAT vs. Static NAT:

  • SNAT: Modifies the source address in packets.
  • Static NAT: One-to-one, permanent mapping of internal to external IP.

• DNAT vs. Dynamic NAT:

  • DNAT: Modifies the destination address in packets.
  • Dynamic NAT: Dynamically maps private IPs to a pool of public IPs, not necessarily involving destination address changes.

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Key Differences

|Feature|SNAT (Source NAT)|DNAT (Destination NAT)|Static NAT|Dynamic NAT| |---|---|---|---|---| |Focus|Changes the source IP|Changes the destination IP|Maps private to public IP|Dynamically maps private IPs| |Type|One-to-many or many-to-one|Many-to-one or one-to-one|One-to-one|Many-to-many or many-to-one| |Use Case|Outbound traffic|Inbound traffic|Hosting servers|Internet access sharing| |Consistency|Can be dynamic|Can be dynamic|Fixed mapping|Dynamic mapping|

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