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After upgrading to FortiClient v7.4.4, a dial-up IKEv2 IPsec tunnel configured to use the AES256-SHA512 proposal for both Phase 1 and Phase 2 is established successfully, but no return traffic is received from the FortiClient.
Traffic flows only in the outbound direction (from FortiGate to FortiClient). Packet capture on FortiGate shows outgoing packets, but no incoming replies.
FG181F-4 # diagnose sniffer packet any 'host 172.10.10.100' 4 0 l
interfaces=[any]
filters=[host 172.10.10.100]
2025-10-27 07:44:33.596218 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:44:34.596242 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:44:35.596264 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:44:36.596282 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:44:37.596300 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
IPsec tunnel configuration:
config vpn ipsec phase1-interface
edit "IKEv2-PSK"
set type dynamic
set interface "port3"
set ike-version 2
set peertype any
set net-device disable
set mode-cfg enable
set ipv4-dns-server1 8.8.8.8
set proposal aes256-sha512 aes128-sha1
set dpd on-idle
set dhgrp 14
set eap enable
set eap-identity send-request
set authusrgrp "Test-Group"
set transport tcp
set ipv4-start-ip 172.10.10.100
set ipv4-end-ip 172.10.10.200
set ipv4-netmask 255.255.255.0
set psksecret ENC M+xOJ/E2xz7z1TK26XpaVZEsxdmwx+CX2klLXT99Ly2fHfzcNKruYvUBFMfvCRuvyZmlOqcU3/pdO
AVGOKUqTbPgt8xZ+1mjHnn6GIwVhoH30vDcw7zioDC+/J0ePeWgUBuzNOY7mmPugZPfJp6G/m8dVmZZkxpYVa
+1lB5cZ5PG3khY8hq2NVqJK2KjvpJyhZtDM1lmMjY3dkVA
set dpd-retryinterval 60
next
end
config vpn ipsec phase2-interface
edit "IKEv2-PSK"
set phase1name "IKEv2-PSK"
set proposal aes256-sha512 aes128-sha1
set dhgrp 14
next
end
In previous versions (v7.4.3 and older), the same configuration worked as expected.
Workaround:
Phase 1 and Phase 2 proposals need to be configured with a different integrity algorithm (for example, sha256 or sha1). Once changed, traffic begins to flow normally in both directions.
config vpn ipsec phase1-interface
edit "IKEv2-PSK"
set proposal aes256-sha256 aes128-sha1
next
end
config vpn ipsec phase2-interface
edit "IKEv2-PSK"
set proposal aes256-sha256 aes128-sha1
next
end
FG181F-4 # diagnose sniffer packet any 'host 172.10.10.100' 4 0 l
interfaces=[any]
filters=[host 172.10.10.100]
2025-10-27 07:42:41.599001 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:42:41.600243 IKEv2-PSK in 172.10.10.100 -> 10.5.137.251: icmp: echo reply
2025-10-27 07:42:42.599027 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:42:42.599807 IKEv2-PSK in 172.10.10.100 -> 10.5.137.251: icmp: echo reply
2025-10-27 07:42:43.599047 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:42:43.599941 IKEv2-PSK in 172.10.10.100 -> 10.5.137.251: icmp: echo reply
2025-10-27 07:42:44.599065 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:42:44.599945 IKEv2-PSK in 172.10.10.100 -> 10.5.137.251: icmp: echo reply
2025-10-27 07:42:45.599082 IKEv2-PSK out 10.5.137.251 -> 172.10.10.100: icmp: echo request
2025-10-27 07:42:45.599943 IKEv2-PSK in 172.10.10.100 -> 10.5.137.251: icmp: echo reply
Note: This issue is reproducible when using IPsec over both TCP and UDP.
This issue is currently under investigation, and a permanent fix will be included in the upcoming FortiClient releases.
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