Tunnel can be built without pre-key configuration when making the IPSEC interconnection in some firewall.
KE is divided into IKE1 and IKE2 versions.
Pre-key configuration is necessary when IPSEC VPN of firewall is IKE v1.
Pre-key configuration is not necessary when IPSEC VPN of firewall is IKE v2. The value of pre-key is “NO” by default.