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cw76's profile

2 Messages

Thursday, March 21st, 2024 3:58 PM

OpenVPN server on Raspberry Pi behind AT&T Fiber using BGW320-505

Hello,

I have an Arris BGW320-505 fiber router/modem.  I had been running an OpenVPN server on a Raspberry Pi behind it for about a year just fine.  Lately, it stopped working and I've been trying to troubleshoot it.  I found that if I set the router to IP Passthrough mode to that Raspberry Pi, OpenVPN works fine.  However, if I don't use IP Passthrough and just use NAT/Gaming to set a port forward for UDP 1194, it kind of works, but doesn't.  What I mean is that I can sometimes connect to my OpenVPN from outside, but it is very slow and it often times out.  Also, once connected, the connection doesn't really work.

The only info I've found that might be related is that if my home is behind a NAT from the ISP (AT&T), and then my router presents a second NAT before getting to my Raspberry Pi, this can disrupt OpenVPN.

How can I determine if this is the case and is it possible to get AT&T to do something on their end to resolve this?  I'd prefer not to use IP Passthrough for security reasons.

Thanks!

ACE - Expert

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35.6K Messages

2 months ago

If you have a BGW320, then it is doing NAT, but the network isn't doing NAT upstream from that.  If you turn on IP Passthrough, then that keeps the BGW320 from doing NAT on the traffic going to/from the IP Passthrough device, which is probably why that's working.   There are probably other ports involved in addition to UDP 1194.

2 Messages

2 months ago

Hmm. OK, good to know that there is no additional NAT upstream. I had read that it is possible for ISPs to NAT upstream. 

Everything I've read indicates that only UDP 1194 needs to be forwarded.

Hopefully someone else is familiar with this situation with OpenVPN specifically and can chime in. 

Thanks! 

(edited)

ACE - Expert

 • 

35.6K Messages

2 months ago

If you were using AT&T Internet Air, then there would be NAT upstream of the Gateway.  But you're using Fiber, so there's not.

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