VPN and NAT-T

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with NAT-T,  When peers detect NAT device in between, from phase1 packet 5, communication switches to UDP/4500, this includes Phase1 packet 5&6, PhaseII Quick mode 3 packets and ESP.

ESP can traverse NAT device if NAT is static.


In the following setup, NAT-T need be disabled even NAT device exists in between:
R10 has the following NAT configuration, note it has NAT for ESP
ip nat inside source static esp 10.0.0.2 interface Ethernet0/1
ip nat inside source static udp 10.0.0.2 500 interface Ethernet0/1 500

in this case, NAT-T won't work because UDP/4500 has no NAT configured on the router. So we need disable NAT-T on ASAv1 to ignore NAT detection for the peer. 
NAT-T setting on ASAv2 doesn't matter because ASAv1 is not behind NAT device.
ASAv1# sh run crypto map
crypto map MAP 10 match address VPN
crypto map MAP 10 set pfs
crypto map MAP 10 set peer 203.0.113.2
crypto map MAP 10 set ikev1 transform-set TRANSFORM
crypto map MAP 10 set nat-t-disable
crypto map MAP 10 set reverse-route
crypto map MAP interface outside



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