Messages

The FortiGate has two Phase2 definitions under the same Phase1:

10.202.159.192/26 <-> 10.200.0.0/14
10.202.159.192/26 <-> 10.224.0.0/11

OPNsense currently has only the first Child SA configured.

Could FortiGate reject Quick Mode if it expects both selectors to be configured on the peer?

Also, OPNsense generates start_action=start while FortiGate has auto-negotiate disable.

Ciao Franco,
the client on his fortinet has these parameters and I have to respect them

[OPNsense 26.1.9]

Hi everyone,
I'm trying to establish a site-to-site IPsec VPN between OPNsense 26.1.9 and a FortiGate.
The IKE Phase 1 comes up successfully, but Phase 2 is always rejected by the FortiGate.
FortiGate configuration
Phase 1

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IKE Version: IKEv1
Mode: Main
Authentication: PSK
Proposal: AES128-SHA256
DH Group: 5 (MODP1536)
Lifetime: 86400
NAT-T: enabled

Phase 2

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PFS: enabled
DH Groups: 14,5
Proposals:
- AES128-SHA1
- AES256-SHA1
- AES128-SHA256
- AES256-SHA256
- AES128-GCM
- AES256-GCM
Lifetime: 43200

Traffic selectors:

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Local:  10.202.159.192/26
Remote: 10.200.0.0/14

There is also a second Phase2 on the FortiGate:

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Local:  10.202.159.192/26
Remote: 10.224.0.0/11

OPNsense configuration
Phase 1

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IKEv1
Main Mode
PSK
AES128-SHA256
DH Group 5

Phase 2

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ESP: AES128-SHA256
PFS Group: 5 (also tested with 14)
Local TS: 10.202.159.192/26
Remote TS: 10.200.0.0/14

Generated swanctl.conf:

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children {
    fae426f8-xxxx {
        esp_proposals = aes128-sha256-modp1536
        local_ts = 10.202.159.192/26
        remote_ts = 10.200.0.0/14
    }
}

What works
IKE Phase 1 is established successfully.
StrongSwan log:

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selected proposal:
IKE:AES_CBC_128/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/MODP_1536
IKE_SA established

Problem
Immediately after IKE_SA establishment, OPNsense sends:

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generating QUICK_MODE request [ HASH SA No KE ID ID ]

The FortiGate immediately responds with:

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received (24576) notify

and rejects Phase 2.
Full log excerpt:

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IKE_SA established
generating QUICK_MODE request [ HASH SA No KE ID ID ]
received (24576) notify

Packet capture
The Quick Mode exchange is visible:

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phase 2/others I oakley-quick[E]

followed immediately by an encrypted Informational packet from the FortiGate.
Question
Even though OPNsense generates:

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esp_proposals = aes128-sha256-modp1536

the Quick Mode log still shows:

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[ HASH SA No KE ID ID ]

which appears to indicate that no PFS/DH exchange is being included in Phase 2.
Is this expected behavior in StrongSwan/OPNsense for IKEv1?
Could this indicate that the Phase2 PFS group is not actually being applied, despite the generated proposal containing

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modp1536?
Has anyone seen FortiGate reject Quick Mode with Fortinet vendor notify

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(24576) under similar circumstances?
Any suggestions on additional debugging steps would be appreciated.
Thanks!