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NAT

Configuring PAT on a cisco device.

todo: explain differences and why what

Static NAT​

todo

Dynamic NAT​

todo

PAT​

  • One public IP for many private IPs. (Overloading)
  • Differentiates multiple sessions using unique port numbers.

Handling Traffic​

  • Outgoing Traffic:
    • Replaces inside local IP and port with inside global IP and unique port.
  • Incoming Responses:
    • Translates inside global IP and port back to the original inside local IP and port.
  • Session Mapping:
    • Creates a translation entry for each new session.
    • Utilizes NAT table for bidirectional flow handling.

Inspecting PAT Translation logs on NAT Router​

show ip nat translations

! Example output from multiple hosts
Pro  Inside global            Inside local       Outside local      Outside global
icmp 11.174.231.225:1         10.40.0.2:1        11.174.231.226:1   11.174.231.226:1
icmp 11.174.231.225:5         10.40.0.1:5        11.174.231.226:5   11.174.231.226:5
icmp 11.174.231.225:8         10.40.0.1:8        11.174.231.226:8   11.174.231.226:8

Configuratiaon​

! Define outside interface (facing to the internet)
interface GigabitEthernet0/1
  ip nat outside

! Define inside interfaces (origin of traffic)
! Can also be a VLAN Interface
interface GigabitEthernet0/0.10
  encapsulation dot1Q 10
  ip address 192.168.10.1 255.255.255.0
  ip nat inside
  no shutdown

interface GigabitEthernet0/0.20
  encapsulation dot1Q 20
  ip address 192.168.20.1 255.255.255.0
  ip nat inside
  no shutdown

! The ACL defines, which source addresses get translated
ip access-list extended nat-inside-in
  permit ip 192.168.10.0 0.0.0.255 any
  permit ip 192.168.20.0 0.0.0.255 any

! The overload keyword enables PAT
ip nat inside source list nat-inside-in interface GigabitEthernet0/1 overload