ipsec.conf

config setup
    charondebug="ike 4, knl 4, cfg 4, net 4, esp 4, dmn 4,  mgr 4"
#    charondebug="ike 2, knl 2, cfg 0"
    uniqueids=no

conn L2TP-PSK-noNAT
    type=transport
    authby=secret
#    pfs=no
    rekey=no
    keyingtries=1
    keyexchange=ikev1
    dpdaction=clear
    dpddelay=300s
    ike=aes128-sha1-modp1024!
    esp=aes128-sha1-modp1024!
    left=%any
    leftprotoport=udp/l2tp
    leftid=@vps.kgtech.fi
    right=%any
    rightprotoport=udp/%any
    auto=add

mikrotik

/interface l2tp-client print
Flags: X - disabled, R - running
 0    name="l2tp-out1" max-mtu=1450 max-mru=1450 mrru=disabled
      connect-to=vps.mydomnain.tld user="xxxxx" password="zzzzzz"
      profile=default-encryption keepalive-timeout=disabled use-ipsec=yes
      ipsec-secret="yyyyyyyy" allow-fast-path=no add-default-route=yes
      default-route-distance=1 dial-on-demand=no
      allow=pap,chap,mschap1,mschap2

strongswan-log

Apr 13 15:24:54 vps2 charon[6498]: 10[KNL] got SPI c47bc73a
Apr 13 15:24:54 vps2 charon[6498]: 10[IKE] Hash(2) => 20 bytes @ 0x7f4f9c0040c0
Apr 13 15:24:54 vps2 charon[6498]: 10[IKE]    0: 78 AE 1F 95 92 8D 5E 48 DE 58 7A 39 D1 C0 5B 3B  x.....^H.Xz9..[;
Apr 13 15:24:54 vps2 charon[6498]: 10[IKE]   16: 39 B8 2B 20                                      9.+
Apr 13 15:24:54 vps2 charon[6498]: 10[ENC] generating QUICK_MODE response 2540116300 [ HASH SA No KE ID ID NAT-OA NAT-OA ]
Apr 13 15:24:54 vps2 charon[6498]: 10[IKE] next IV for MID 2540116300 => 16 bytes @ 0x7f4f9c003a30
Apr 13 15:24:54 vps2 charon[6498]: 10[IKE]    0: 03 04 03 B8 17 ED 4B E1 56 C5 4B 16 AC 6C F6 95  ......K.V.K..l..
Apr 13 15:24:54 vps2 charon[6498]: 10[NET] sending packet: from 10.16.14.35[4500] to 82.203.164.223[52258] (332 bytes)
Apr 13 15:24:54 vps2 charon[6498]: 04[NET] sending packet: from 10.16.14.35[4500] to 82.203.164.223[52258]
Apr 13 15:24:54 vps2 charon[6498]: 10[MGR] checkin IKE_SA L2TP-PSK-noNAT[2]
Apr 13 15:24:54 vps2 charon[6498]: 10[MGR] checkin of IKE_SA successful
Apr 13 15:24:54 vps2 charon[6498]: 03[NET] received packet => 80 bytes @ 0x7f4fc8051520
Apr 13 15:24:54 vps2 charon[6498]: 03[NET]    0: 00 00 00 00 CB 56 AA D8 07 8B 32 42 38 39 7C 0F  .....V....2B89|.
Apr 13 15:24:54 vps2 charon[6498]: 03[NET]   16: DE CC 56 05 08 10 05 01 AB EB 94 C2 00 00 00 4C  ..V............L
Apr 13 15:24:54 vps2 charon[6498]: 03[NET]   32: 66 1E 16 CE 15 4F 22 10 34 35 70 99 29 38 48 5E  f....O".45p.)8H^
Apr 13 15:24:54 vps2 charon[6498]: 03[NET]   48: 7D 0B B9 F2 30 13 AF C4 76 19 71 94 F9 A1 E3 C4  }...0...v.q.....
Apr 13 15:24:54 vps2 charon[6498]: 03[NET]   64: 4E 01 C8 16 35 B9 4F 8B 12 A4 13 75 11 C3 6C 4B  N...5.O....u..lK
Apr 13 15:24:54 vps2 charon[6498]: 03[NET] received packet: from 82.203.164.223[52258] to 10.16.14.35[4500]
Apr 13 15:24:54 vps2 charon[6498]: 03[NET] waiting for data on sockets
Apr 13 15:24:54 vps2 charon[6498]: 12[MGR] checkout IKEv1 SA by message with SPIs cb56aad8078b3242_i 38397c0fdecc5605_r
Apr 13 15:24:54 vps2 charon[6498]: 12[MGR] IKE_SA L2TP-PSK-noNAT[2] successfully checked out
Apr 13 15:24:54 vps2 charon[6498]: 12[NET] received packet: from 82.203.164.223[52258] to 10.16.14.35[4500] (76 bytes)
Apr 13 15:24:54 vps2 charon[6498]: 12[IKE] next IV for MID 2884342978 => 16 bytes @ 0x7f4f9c002170
Apr 13 15:24:54 vps2 charon[6498]: 12[IKE]    0: EA B5 20 9D 0D FF 5C E4 EE 89 B3 B2 AB B2 3E 9B  .. ...\.......>.
Apr 13 15:24:54 vps2 charon[6498]: 12[ENC] parsed INFORMATIONAL_V1 request 2884342978 [ HASH N(ATTR_UNSUP) ]
Apr 13 15:24:54 vps2 charon[6498]: 12[IKE] Hash => 20 bytes @ 0x7f4f9c0041f0
Apr 13 15:24:54 vps2 charon[6498]: 12[IKE]    0: 69 6F 8E 93 5E 1B 2C 33 01 31 04 70 CD 74 0B 62  io..^.,3.1.p.t.b
Apr 13 15:24:54 vps2 charon[6498]: 12[IKE]   16: A3 F9 A6 AB                                      ....
Apr 13 15:24:54 vps2 charon[6498]: 12[IKE] received ATTRIBUTES_NOT_SUPPORTED error notify
Apr 13 15:24:54 vps2 charon[6498]: 12[MGR] checkin IKE_SA L2TP-PSK-noNAT[2]
Apr 13 15:24:54 vps2 charon[6498]: 12[MGR] checkin of IKE_SA successful
Apr 13 15:24:56 vps2 charon[6498]: 11[MGR] checkout IKEv1 SA with SPIs 2a52282b71f87f24_i f9cb577f9ab251d6_r
Apr 13 15:24:56 vps2 charon[6498]: 11[MGR] IKE_SA checkout not successful
Apr 13 15:24:58 vps2 charon[6498]: 13[MGR] checkout IKEv1 SA with SPIs cb56aad8078b3242_i 38397c0fdecc5605_r
Apr 13 15:24:58 vps2 charon[6498]: 13[MGR] IKE_SA L2TP-PSK-noNAT[2] successfully checked out
Apr 13 15:24:58 vps2 charon[6498]: 13[MGR] checkin IKE_SA L2TP-PSK-noNAT[2]
Apr 13 15:24:58 vps2 charon[6498]: 13[MGR] checkin of IKE_SA successful