NAT order of operations

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Inside-to-Outside Outside-to-Inside
  • If IPSec then check input access list
  • decryption – for CET (Cisco Encryption Technology) or IPSec
  • check input access list
  • check input rate limits
  • input accounting
  • redirect to web cache
  • policy routing
  • routing
  • NAT inside to outside (local to global translation)
  • crypto (check map and mark for encryption)
  • check output access list
  • inspect (Context-based Access Control (CBAC))
  • TCP intercept
  • encryption
  • Queueing
  • If IPSec then check input access list
  • decryption – for CET (Cisco Encryption Technology) or IPSec
  • check input access list
  • check input rate limits
  • input accounting
  • redirect to web cache
  • NAT outside to inside (global to local translation)
  • policy routing
  • routing
  • crypto (check map and mark for encryption)
  • check output access list
  • inspect CBAC
  • TCP intercept
  • encryption
  • Queueing

Note that the process is merely the same. But for inside process the NAT is performed after routing. As for outside the NAT if performed before routing. Which seems pretty logical 😉

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