f6a461ee_IPsec_VPN___UntangleWiki__Description
[Name] Authentication and SA/Key Exchange [Description] 
If you leave the Phase 1 and Phase 2 manual configuration checkboxes disabled, IPsec will attempt to automatically negotiate the encryption protocol with the remote peer when creating the tunnel. Given the number of different IPsec implementations and versions, as well as the overall complexity of the protocol, best results can often be achieved by enabling manual configuration of these two options, and selecting Encryption, Hash, DH Key Group, and Lifetime values that exactly match the settings configured on the peer device.
IPsec VPN - UntangleWiki
Description