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Order of Operations

Table 9 displays the order of operations for both inside-to-outside and outside-to-inside translation.





 Table 9:  NAT Order of Operations


 Inside-to-Outside Translation


 Outside-to-Inside Translation




    
  
  1.  Inside (privately addressed) traffic enters the router on an interface marked as "inside."
    2. 
  
  2.  A route lookup is performed.
    3. 
  
  3.  If the next interface is marked as "outside," the router sends the traffic to the server module.
    4. 
  
  4.  The server module performs the appropriate translation.
    5. 
  
  5.  The router forwards the packet to the appropriate egress line card.
    6. 
  
  6.  The line card sends the packet as outbound traffic using a globally unique source address (inside source translation), destination address (outside source translation), and ports (NAPT).
    7. 




    
  
  1.  Traffic from the outside, public domain enters the router.
    2. 
  
  2.  All traffic from an interface that is marked "outside," whether or not it requires NAT, is sent to the server module.
    3. 
  
  3.  The server card looks for an associated NAT match.
    4. 
  
  4.  If the server module:
    5. 


  
    
    
  •  Finds a NAT match, and the destination interface is marked as "inside," the server module performs the appropriate translation and sends the packet to the appropriate destination.
    • 
    
  •  Does not find a NAT match, and the destination interface is marked as "inside," the server module drops the packet.
    • 
    
  •  Does not find a NAT match, and the destination interface is not marked as "inside," the server module processes the packet normally for its destination.
    •
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