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I have a primary OpenVPN server (site A) hosted on-prem with multiple site-to-site connections; one of these sites is a satellite office (site B). Under normal operation, site B is a site-to-site client of A and exposes it's subnet to site A and one additional subnet/site that only site B has access to via a separate VPN.

I'd like to spin up an OpenVPN server at site B that mirrors the site A server except for the site A <> site B connection to act as a backup if site A goes offline.

All these sites use the embedded OpenVPN frontend on NGFW/untangle

So far, spinning up a server at Site B while the Site A <> Site B connection is live and connecting to Site B's server with new credentials, the VPN connects then drops after <30s. Is this an issue with reusing the VPN's assigned port? What would cause this behavior?

EDIT1: Adding block diagrams for clarity. The solid line are existing, and the dotted lines are proposed. Basically, if site A goes offline, connections to the other sites can be accessed via the site B VPN server. None of the subnets overlap site-to-site, and both servers are using port 1194. Currently checking logs. block diagram of network topology

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  • Can you add some more details like example IPs/ports each device is using, or a simple diagram? Which VPN connection drops? Did you look at the logs to see the reason it's dropping?
    – Cpt.Whale
    Commented Dec 9 at 18:39
  • If you mean the new connections, like Site C <> Site B drop, then you might need to look for typical openvpn drop causes like MTU size/fragmentation. In UDP mode, the tunnel can show connected status (even if it never gets anything back) until timeout, have you checked that traffic actually flows for that first 30 seconds or so? Using the same server port shouldn't matter, since the source-port is randomized by the client
    – Cpt.Whale
    Commented Dec 10 at 17:07
  • I haven't attempted a Site C <> Site B connection yet. The current issue is that with my direct connection to Site B. Wanted to establish that first before moving on to site-to-site.
    – dschon
    Commented Dec 11 at 21:25
  • So the connection that drops is what, User 1 > Site B? That shouldn't have anything to do with the other sites at least. I would still check for those typical issues, and any small config differences between serverA/B
    – Cpt.Whale
    Commented Dec 11 at 22:27

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