Which IP fields are changed when encrypting between 2 peers?

[joseph_samaha]

Hi, When establishing a VPN tunnel between 2 peers i have one banking application on the LAN that hang up.This application also is using encryption between its 2 servers.Is there an IP field that it is changed during IKE phases so it will interfere on the application de-encryption process and make the application hanging up? Thank you.

[m.sir]

It dependes if you use IPsec tunnel or transport mode and if you use ESP or AH or both

With AH there is no encryption with ESP transport mode is encrypted TCP(UDP) header and IP payload with tunnel mode is encrypted original IP header, TCP(UDP) header and payload

[joseph_samaha]

I am using ESP and AH.I can use tunnel or transport mode. But i need to know which fields are changed to coordinate with the Application's engineer. It seems it is sensible to one of the IP header field change.

[joseph_samaha]

What about IPSec inflence on CRC field.