Changing the tunnel_keepalive_method value for a gateway causes it to use DPD instead of Check Point's proprietary tunnel_test protocol in all VPN Communities set for Permanent Tunnels that the gateway is a member of. By default whenever policy is installed to a gateway, it will clear all IKE Phase 1 tunnels which will have an immediate impact to existing VPNs upon policy installation unless the checkbox keep_IKE_SAs is checked under Global Properties...Advanced...Configure. You'll definitely want to familiarize yourself with these SKs:
sk108600: VPN Site-to-Site with 3rd party
sk97746: New VPN features in R77.10
DPD is an industry standard extension to IKEv1 and you can read about how it works here: https://www.ietf.org/rfc/rfc3706.txt . DPD is ingrained by design in IKEv2.
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