set vpn ipsec authentication psk PSK id '192.0.2.1'
set vpn ipsec authentication psk PSK id '192.0.2.2'
set vpn ipsec authentication psk PSK secret '1234567890'
set vpn ipsec esp-group ESP-group lifetime '3600'
set vpn ipsec esp-group ESP-group mode 'tunnel'
set vpn ipsec esp-group ESP-group pfs 'enable'
set vpn ipsec esp-group ESP-group proposal 1 encryption 'aes256'
set vpn ipsec esp-group ESP-group proposal 1 hash 'sha1'
set vpn ipsec ike-group IKE-group key-exchange 'ikev2'
set vpn ipsec ike-group IKE-group lifetime '28800'
set vpn ipsec ike-group IKE-group proposal 1 encryption 'aes256'
set vpn ipsec ike-group IKE-group proposal 1 hash 'sha1'
set vpn ipsec interface 'eth1'
set vpn ipsec log level '2'
set vpn ipsec site-to-site peer OFFICE-B authentication local-id '192.0.2.1'
set vpn ipsec site-to-site peer OFFICE-B authentication mode 'pre-shared-secret'
set vpn ipsec site-to-site peer OFFICE-B authentication remote-id '192.0.2.2'
set vpn ipsec site-to-site peer OFFICE-B connection-type 'initiate'
set vpn ipsec site-to-site peer OFFICE-B ike-group 'IKE-group'
set vpn ipsec site-to-site peer OFFICE-B local-address '192.0.2.1'
set vpn ipsec site-to-site peer OFFICE-B remote-address '192.0.2.2'
set vpn ipsec site-to-site peer OFFICE-B tunnel 0 esp-group 'ESP-group'
set vpn ipsec site-to-site peer OFFICE-B tunnel 0 local prefix '100.64.1.0/24'
set vpn ipsec site-to-site peer OFFICE-B tunnel 0 remote prefix '100.64.2.0/24'

vyos@r14# cat /etc/strongswan.d/charon-logging.conf 

charon {
    syslog {
        # prefix for each log message
        identifier = charon
        # use default settings to log to the LOG_DAEMON facility
        daemon {
            default = 1
            ike_name = yes
        }
    }
}