How NAT-Traversal works in IPsec

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In first two packet, it will negotiate NAT-T compatibility 

1st Message in Main mode:




2nd Message in main mode:


In 3rd and 4th Message, it will exchange hash of IP address and Port.

3rd Message main mode:



4th Message in main mode


Debug on FGT:

ike 0: comes 10.1.1.20:500->10.1.1.10:500,ifindex=4....
ike 0: IKEv1 exchange=Identity Protection id=987e2067d9c61bc0/3954de8f43e2c2c0 len=348
ike 0: in 987E2067D9C61BC03954DE8F43E2C2C004100200000000000000015C0A000104CD2F264257D538BA3EC01D4446EB541E8923
ike 0:VPN:14: responder:main mode get 2nd message...
ike 0:VPN:14: received NAT-D payload type 20   
ike 0:VPN:14: received NAT-D payload type 20
ike 0:VPN:14: NAT not detected  <<-----------------------     

If hash matches, there is no NAT device in between and It continue to use same port 500 for remaining
communication



If there is NAT device in between both peer:==>

3rd message in main mode:



4th message in main mode:


ike 0:VPN:3: initiator: main mode get 2nd response...
ike 0:VPN:3: received NAT-D payload type 20
ike 0:VPN:3: received NAT-D payload type 20
ike 0:VPN:3: NAT detected: ME 
ike 0:VPN:3: NAT-T float port 4500
ike 0:VPN:3: ISAKMP SA d3701b9bc03e3e03/fa02fbc561fe5763 key 8:347A5B142951CC0F

5th Message in main mode:








Comments

  1. Unknown11 February 2022 at 22:53

    amazing content!!! This doc has cleared all my doubts regarding NAT TRAVERSAL

    ReplyDelete
  2. Unknown19 March 2022 at 07:25

    Awesome content

    ReplyDelete

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