How to set up IPSec VPN properly within multiple sites?

[iamyi]

Hi fellows, hope you can help on this.

I have 3 sites, site A, B, C. Site A is the main site, and I would like to setup site B, C connected to site A using IPSec VPN tunnels.

I set up the tunnel between A & B, it's working fine. But when I set up the tunnel between A & C, it's not working properly, either not connecting or drop after certain period of time.

Each site has unique subnets, so there are no overlap. Any idea why this is happening? Thank you.

[iamyi]

Well, updates from the poster. I don't know if there are specific settings needed when multiple VPN tunnels are set, but I don't think there should be. What I found is that although site C has a static public IP address and tunnel can be up sometimes, it's somehow behind NAT (I guess). Ping is allowed on the WAN port, but I cannot ping the public IP from external network, which makes me think it's behind NAT. Now I created a dial-up IPSec VPN instead for site C to connect site A, and will leave it running for a few days to see if it's stable.