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Weird Wireguard issues I could use some help with.

I've hit a wall with a weird Wireguard issue. I'm trying to connect my phone (over cell) to my home router using wireguard and it will not connect.

  • The keys are all correct.
  • The IPs are all correct.
  • The ports are open on the firewall.
  • My router has a public IP, no CGNAT.

The router is opnsense, I have a tcpdump session going and when I attempt a connection from the phone I see 0 packets on that port. I am able to ping the router and reach the web server sitting behind it from the phone.

I have a VPS that I configured WG on and the phone connects fine to that. I also tested configuring the VPS to connect to my home router and that also works fine.

I'm really at a loss as to where to go next.

Edit 2: I completely blew out the config on both sides and rebuilt it from scratch, using a different UDP port, and it all appears to be working now. Thanks for everyone's help in tracking this down.

Edit: It was requested I provide my configs.

opnsense:

 undefined
    
####################################################
# Interface settings, not used by `wg`             #
# Only used for reference and detection of changes #
# in the configuration                             #
####################################################
# Address =  172.31.254.1/24
# DNS =
# MTU =
# disableroutes = 0
# gateway =

[Interface]
PrivateKey = 
ListenPort = 51821

[Peer]
# friendly_name = note20
PublicKey = 
AllowedIPs = 172.31.254.100/32

Android:

 undefined
    
[Interface]
Address = 172.31.254.100/32
PrivateKey = 

[Peer]
AllowedIPs = 0.0.0.0/32
Endpoint = :51821
PublicKey =
29 comments

  • The allowed IP's for your peer should be 0.0.0.0/0 NOT /32. (That literally means that only IP 0.0.0.0 is allowed). I'm pretty sure that's your problem since 0.0.0.0 is not a valid IP that anyone is assigned.

  • This probably does not apply for you but don't try sending wg over port 53, learned the hard way some routers simply won't pass non-dns packets there.

    Otherwise considering you are able to access VPS stuff from phone but not the router connected to the same VPS then I would check

    • if forwarding is enabled on the vps
    • if you can't see any packets on the router side then it sounds like a routing issue at the vps

    E: I am too baked and assumed you are trying to have the VPS as a central hop point.

  • Is wireguard hosted on opnsense, or an internal device that the port is being forwarded to?

    If it's on opnsense, be sure you route outgoing traffic on that port over the correct gateway, possibly even an extra rule to be sure the proper reply-to is set. Opnsense used to do the gateway routing configuration automatically, but once wg got added to the kernel, you're now required to manually specify the gateway in your rules for it to work properly.

    Also, if you see zero packets, then as others mentioned, try a different mtu. Some service providers (mobile, and even hotels) try to block all VPN traffic altogether and they do this by measuring the mtu of the packets. A little tweaking might get it to work, although I'd expect this to have held true for the VPS too, honestly.

    • Is wireguard hosted on opnsense, or an internal device that the port is being forwarded to? opnsense. I do have the interface and gw configured and was able to successfully connect when I did the test config from my VPS.

      Also, if you see zero packets, then as others mentioned, try a different mtu. Some service providers (mobile, and even hotels) try to block all VPN traffic altogether and they do this by measuring the mtu of the packets.

      I didn't think about MTU. I'll do some research and testing on this today.

      A little tweaking might get it to work, although Iโ€™d expect this to have held true for the VPS too, honestly.

      This is why I'm struggling. Every test I do is successful, by all rights this should be working. Phone to VPS, GOOD. VPS to opnsense, GOOD. Phone to VPS, BAD. Can I see packets from the phone to opnsense, YES, unless it's wireguard.

      I'll experiment with MTU and see if that bears and fruit. Thanks.

  • Did you setup a NAT on the firewall? You have to setup a static NAT on the interface that your Public IP sits on and to the private IP address of your VPS (you are using a private network space from one of the other interfaces on your FW right?).

    Make sure that the policy that you create with the NAT includes UDP 51820 (unless you changed the default port) People often mistake using TCP which is a different protocol. If that doesnโ€™t work, then look at the traffic on your FW

    • There's some confusion here. I'm running wireguard on my opnsense router and I'm trying to connect my Android phone to it.

      I just used the VPS to help troubleshoot to show other clients can connect to opnsense AND the phone can connect to other servers but the phone and opn won't talk.

      I know this screams config issue. I've gone over it and rebuilt it multiple times. I can't find anything wrong. Someone else asked to see configs so I'll post those tomorrow.

      • It is a config issue. Allowed IPs for your client should be 0.0.0.0/0 not 0.0.0.0/32

    • Meant to say if you still get stuck, run Wireshark on your FW and your VPS and run a tcp dump and filter the traffic to see where the data stops.

      You can also use traceroute to your public IP on the port 51820 and check your connectivity or even curl: -v http:////publicip:51820

      • Yeah I would probably try if the phone can actually access anything on that port.

        On router: netcat -vvvl 0.0.0.0 51820
        On phone: http://router_ip:51820

        The browser will fail opening it but on router you should see the first incoming HTTP GET packet.
        Or one could run a local shell on the phone (assuming android) and try netcat too.

        (or this http server one liner python3 -m http.server can be used instead of netcat)

29 comments