Dialup IPSec VPN issues with Phase 1

[systemgeek]

FortiGate - 7.6.3

FortiClient - 7.2.9 (Windows and Mac)

I have been working with Support for weeks now with no success so hoping I can get help here.

Fortigate config:

config vpn ipsec phase1-interface
edit "OpsIPSecVPN"
set type dynamic
set interface "port1"
set ike-version 2
set peertype any
set net-device disable
set mode-cfg enable
set proposal des-sha512 aes256-sha512
set comments "VPN: OpsIPSecVPN -- Created by VPN wizard"
set dhgrp 14
set wizard-type dialup-forticlient
set nattraversal disable
set network-overlay enable
set network-id 0
set transport tcp
set fortinet-esp enable
set assign-ip-from name
set dns-mode auto
set ipv4-split-include "OpsIPSecVPN_split"
set ipv4-name "VPN_PCI_Operations_us2"
set save-password enable
set client-auto-negotiate enable
set client-keep-alive enable
set psksecret ENC ***

FortiClient config:

<connection>

<name>us2-LOACAL2</name>

<type>manual</type>

<ike_settings>

<keep_fqdn_resolution_consistency>0</keep_fqdn_resolution_consistency>

<version>2</version>

<eap_method>0</eap_method>

<sso_enabled>0</sso_enabled>

<ike_saml_port>0</ike_saml_port>

<use_external_browser>0</use_external_browser>

<fido_auth>0</fido_auth>

<prompt_certificate>0</prompt_certificate>

<description></description>

<server>vpn.example.com</server>

<authentication_method>Preshared Key</authentication_method>

<auth_key></auth_key>

<auth_data>

<preshared_key>Enc ********</preshared_key>

<certificate></certificate>

</auth_data>

<mode>aggressive</mode>

<dhgroup>14</dhgroup>

<key_life>86400</key_life>

<localid></localid>

<nat_traversal>0</nat_traversal>

<networkid>0</networkid>

<sase_mode>0</sase_mode>

<mode_config>1</mode_config>

<enable_local_lan>0</enable_local_lan>

<enable_ike_fragmentation>0</enable_ike_fragmentation>

<dpd>1</dpd>

<xauth>

<enabled>1</enabled>

<prompt_username>0</prompt_username>

<username>Enc XXXXXXXXX</username>

<password>Enc *********</password>

</xauth>

<proposals>

<proposal>DES|SHA512</proposal>

<proposal>AES256|SHA256</proposal>

</proposals>

<fgt>0</fgt>

</ike_settings>

<ipsec_settings>

<remote_networks></remote_networks>

<dhgroup>14</dhgroup>

<key_life_type>seconds</key_life_type>

<key_life_seconds>86400</key_life_seconds>

<key_life_Kbytes>5120</key_life_Kbytes>

<replay_detection>0</replay_detection>

<pfs>1</pfs>

<use_vip>1</use_vip>

<virtualip>

<type>modeconfig</type>

<ip></ip>

<mask></mask>

<dnsserver></dnsserver>

</virtualip>

<proposals>

<proposal>DES|SHA512</proposal>

<proposal>AES256|SHA256</proposal>

</proposals>

<ipv4_split_exclude_networks></ipv4_split_exclude_networks>

</ipsec_settings>

<on_connect>

<script>

<os>mac</os>

<script>$null</script>

</script>

</on_connect>

<on_disconnect>

<script>

<os>mac</os>

<script>$null</script>

</script>

</on_disconnect>

<tags>

<allowed></allowed>

<prohibited></prohibited>

</tags>

<host_check_fail_warning></host_check_fail_warning>

<keep_running>0</keep_running>

<disclaimer_msg>$null</disclaimer_msg>

<ui>

<show_passcode>0</show_passcode>

<show_remember_password>0</show_remember_password>

<show_alwaysup>0</show_alwaysup>

<show_autoconnect>0</show_autoconnect>

<save_username>0</save_username>

<save_password>0</save_password>

</ui>

</connection>

</connections>

</ipsecvpn>

Regardless of Encryption - Authentication on either side I get "no proposal chosen" "Negotiate SA Error".  Whats more interesting is what the Client seems to be sending to the FortiGate:

2025-05-13 14:53:35.412782 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: incoming proposal:
2025-05-13 14:53:35.412945 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: proposal id = 1:
2025-05-13 14:53:35.412951 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: protocol = IKEv2:
2025-05-13 14:53:35.413111 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: encapsulation = IKEv2/none
2025-05-13 14:53:35.413117 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=ENCR, val=AES_CBC (key_len = 256)
2025-05-13 14:53:35.413279 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=INTEGR, val=AUTH_HMAC_SHA2_512_256
2025-05-13 14:53:35.413284 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA
2025-05-13 14:53:35.413445 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA2_512
2025-05-13 14:53:35.413451 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA2_384
2025-05-13 14:53:35.413611 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA2_256
2025-05-13 14:53:35.413616 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=DH_GROUP, val=MODP2048.
2025-05-13 14:53:35.413950 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: proposal id = 2:
2025-05-13 14:53:35.414123 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: protocol = IKEv2:
2025-05-13 14:53:35.414128 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: encapsulation = IKEv2/none
2025-05-13 14:53:35.414299 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=ENCR, val=AES_CBC (key_len = 256)
2025-05-13 14:53:35.414304 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=INTEGR, val=AUTH_HMAC_SHA2_256_128
2025-05-13 14:53:35.414474 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA
2025-05-13 14:53:35.414478 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA2_512
2025-05-13 14:53:35.414483 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA2_384
2025-05-13 14:53:35.414487 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=PRF, val=PRF_HMAC_SHA2_256
2025-05-13 14:53:35.414492 ike V=root:0:6bbf3efb5a59b188/0000000000000000:690: type=DH_GROUP, val=MODP2048.

The first part of that incoming proposal says IKEv2 with AES_CBC key length 256, SHA512.  But where is DES since thats the first option in the client.  The proposal from the FortiGate does say val=DES_CBC.

To me this is say that the ForitClient is ignoring the config when sending the proposal.

Has anyone else seen this????

[funkylicious · Accepted solution]

i assume that you are trying to do ipsec w/ tcp and ikev2.

try using at least FortiClient 7.4.1 which would support this setup and choose only 1 set of params for phase1, dont enable/configure multiple options.

have a look at this also, https://community.fortinet.com/t5/Support-Forum/FortiClient-Remote-Access-IPsec-over-TCP-not-working... 

[systemgeek]

I read through that doc you posted.  I can say that with FortiOS 7.6.3 FCT 7.2.9 and 7.4.3 setting the Encapsulation on the client to IKE UDP port 4500 gets a response on the FGT.  The same is true with Auto.  However, IPSec over TCP never makes it to the FGT.  I think its doing a retransmission when set to IPSec over TCP.

I do not know anything about FCT 7.4.8 which was mentioned in that doc.

[funkylicious]

FortiOS 7.4.8 is to be available this month if i understood correctly

[systemgeek]

Waiting with bated breath...