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I have recently noticed a strange behavior with OpenVPN client.

Say I do a mtr vpn_server_ip BEFORE connecting the VPN client. Everything is fine, the route is displayed as expected.

Once connected I have the VPN client connected with the proper routes and gateway set up for everything to go by the VPN, save of course vpn_server_ip. but then I get nothing from the mtr, first hop responds (my home router) but all subsequent hops fail.

I dont see any difference in route -n that would explain this change...

It is a minor problem really, doesn't affect (afaik) the working of the vpn but it is puzzling.

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1 Answer 1

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Are you using the tun device or the tap device? tun is routed but tap is bridged, which could affect whether you can access the server IP or not. If it's a bridged connection then maybe you can't access the server IP.

However this really looks like a firewall issue and your openvpn server firewall is blocking icmp traffic. That would explain why mtr and ping both don't work as they both use icmp.

Check with the admin of the openvpn server and see what they have fora a firewall config. Also you could try running nmap against the host to see what ports are blocked. You should probably only do that with the permission and understanding of the openvpn server admin though, as that could cause a lot of log messages and warnings on the remote side.

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I am the server admin and I have no reason to believe that ICMP is blocked. I use tun. –  zanfr Mar 21 '11 at 20:09
    
oh ok, so check your iptables on the server with 'iptables -nvL' and see if you have rules explicitly allowing the proper sorts of icmp queries. I suspect you are blocking them by default. –  Phil Hollenback Mar 21 '11 at 20:43

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