VPN Port Open but Can't Telnet or Connect

VPN
1

Trying to setup up the VPN server but clients can’t connect, when checking I’ve found the following:

  1. Port is open on the box, checked with netstat command
  2. Can’t telnet to that port from inside the same LAN as the DS218+

Have setup OpenVPN with all the default settings. Also checked and currently the firewalls are not switched on.

Not sure what else to try, anyone had the same issue?

2

Tcp or udp? If udp you can’t telnet. Try to nmap your server

3

VPN client logs would typically allow you to see if any response was received from your VPN server.
For blocked ports you would see typically see either an immediate connection closure (typically firewall) or a timeout message followed by retry attempts.
Not forgetting that if you want to get on down and dirty installing wireshark on a client will reveal much detail.
Particularly useful for diagnosing the negotiations of options.
As UDP connections are stateless a telnet equivalent would of much less value.

4

as you didn’t state anything about portforwarding on your router so that any outside client is redirected to the openvpn port on the synology, what did you define there (I myself forward port 443 UDP from the outside to the default openvpn port on my own vpn server running on a raspberry pi)? assuming that the clients are actually from the outside intending to get into your (home?) network?

so in my case the client openvpn profiles states to connect to port 443 UDP of the DNS entry of the external connection of my internet modem/router (I don’t have to use any DDNS service as ip is fixed but still prefer to use a DNS name and not the ip address):

proto udp
remote xxx.yyy.com 443

I don’t assume that your clients are within your network, trying to get unto the internet? for such a setup I’d expect one to use a hosted (external) vpn service not a vpn server you host yourself within your own network…

what is the error you get when trying to enable the vpn on the client?

5

It is UDP so maybe that’s it… whoops! Okay so nmap does show the port opening… don’t suppose you know of a way to check port forwarding over UDP? As if the port is opening maybe my port fowarding is going wrong somewhere… although pretty sure my setup is correct.