Specifications

NAT Overview
September 08, 2010 Page 4 of 18
WhenServer1respondstoClient1,itspacketarrivesattheNATrouterwithClient1’stranslated
addressof200.1.1.1asthedestinationaddress,butleavestheNATrouterwithClient1’sactual
addressof10.1.1.1asthedestinationaddress.Server1’sresponseisdeliveredtoIPaddress10.1.1.1.
Figure 1 Basic NAT Static Inside Address Translation
NAPT Static Inside Address Translation
Figure 2onpage 5displaysabasicNAPTstaticinside addresstranslationoverview.Client1hasa
sourceIPaddressof10.1.1.2andL4portof125(itsownIPaddressandport)andadestination
addressof200.1.1.50andL4portof80(theServer1IPaddressandport).Thestatictranslation
is
configuredbetweenthelocalIPaddress(Client1’sownIPaddressandport)andtheglobalIP
address200.1.1.1andL4port1025(anavailablepublicnetworkaddressandport).
ApacketarrivesattheNATrouterfromClient1withasourceaddressof10.1.1.2:125,butleaves
theNATrouter
withasourceaddressof200.1.1.1:1025.Inbothcasesthedestinationisfor
Server1’sIPaddressof200.1.1.50:80.FromServer1’spointofview,Client1’sIPaddressis
200.1.1.1:1025.Server1doesn’tknowanythingaboutitsactualIPaddressof10.1.1.2:125.
WhenServer1respondstoClient1,itspacketarrivesattheNATrouter
withClient1’stranslat ed
addressof200.1.1.1:1025asthedestinationaddress,butleavestheNATrouterwithClient1’s
actualaddressof10.1.1.2:125asthedestinationaddress.Server1’sresponseisdeliveredtoIP
address10.1.1.2:125.
Client1
10.1.1.1
Server1
200.1.1.50
NAT
ROUTER
DA: 200.1.1.50
SA: 200.1.1.1
External
Public
Network
Internal
Private
Network
DA: 200.1.1.1
SA: 200.1.1.50
DA: 200.1.1.50
SA: 10.1.1.1
DA: 10.1.1.1
SA: 200.1.1.50