Unable to establish a connection on VPN Tunnel 2

Question

I'm working with a partner who has a SonicWall firewall (NSA 6.5) and we're attempting to establish a Site-To-Site VPN between my AWS VPN and his SonicWall.   We are able to get tunnel 1 up and active, but tunnel 2 throws the following error.   Does anyone have a thought on what causes the following error we are seeing in CloudWatch?

Thanks for any suggestions,
DB

{
    "event_timestamp": 1669073636,
    "details": "AWS tunnel was unable to decrypt the security payload(s)",
    "dpd_enabled": true,
    "nat_t_detected": true,
    "ike_phase1_state": "established",
    "ike_phase2_state": "down"
}

Tushar_J · Answer

There are specific troubleshooting instructions in this Knowledge base article for VPN Phase2 issues:

https://aws.amazon.com/premiumsupport/knowledge-center/vpn-tunnel-phase-2-ipsec/

Can you clarify if you are using Policy based VPN or Route based VPN, if route based is it Static route based or BGP?

Lastly, are you using IKEv1 or IKEv2?

If you are using IKEv2 you can change the Start-up action for the VPN, see this [documentation](https://docs.aws.amazon.com/vpn/latest/s2svpn/initiate-vpn-tunnels.html)

**Startup action**: The action to take when establishing the VPN tunnel for a new or modified VPN connection. By default, your customer gateway device initiates the IKE negotiation process to bring the tunnel up. You can specify that AWS must initiate the IKE negotiation process instead.

Hari Karthigasu · Answer

To activate both tunnels. The ipsec tunnel config should have `overlapip=yes` parameter set. By default, it is `no`.
From ipsec spec,
```
a boolean (yes/no) that determines, when (left|right)subnet=vhost: is used, if the virtual IP claimed by this states created from this connection can with states created from other connections.
Note that connection instances created by the Opportunistic Encryption or PKIX (x.509) instantiation system are distinct internally. They will inherit this policy bit.
The default is no.
This feature is only available with kernel drivers that support SAs to overlapping conns. At present only the (klips) mast protocol stack supports this feature.
```

Unable to establish a connection on VPN Tunnel 2

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