Enhance troubleshooting: tunnels down, but IPSEC is up

[ckamps]

Enhance the troubleshooting section to help people figure out conditions in which the tunnels are shown as down but IPSEC is up. This may be due to BGP not being established across both tunnels.

[maximillianus]

Hi @ckamps , I actually encountered this issue where IPSEC is up but Tunnels are down. I see that in my strongSwan's BGP summary, the BGP's state is Active but Up/Down status is listed as never. May I know how to fix this?
By the way, the configuration works if I use Static routing instead of Dynamic routing.

[fortran01]

In my case, I have to redo the Site-to-Site VPN connection and indicate an anything (0.0.0.0/0) for Remote IPv4 network CIDR and Local IPv4 network CIDR. My guess is because BGP traffic routes on the public IP attached to strongSwan, meaning over the VPC Internet Gateway, so I could not use my VPC CIDRs.