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Re: [Openvpn-users] --redirect-gateway makes DHCP-ip default gw [SOLVED]


  • Subject: Re: [Openvpn-users] --redirect-gateway makes DHCP-ip default gw [SOLVED]
  • From: Mathias Sundman <mathias@xxxxxxxxxx>
  • Date: Wed, 15 Dec 2004 21:34:40 +0100 (CET)

On Wed, 15 Dec 2004, Ferenc-Jan wrote:

I am having problems with 2.0 server (1.6/2.0 p2p work fine) between W2K and Linux. Tunnel gets set up successfully (ping, smb works), but the w2k routing table looks strange to me. The tunnel entries are:
192.168.4.1 255.255.255.255 192.168.4.5 192.168.4.6 1
192.168.4.4 255.255.255.252 192.168.4.6 192.168.4.6 1
192.168.4.6 255.255.255.255 127.0.0.1 127.0.0.1 1

The routing table above looks correct. Windows does not support true Point-to-Point tunnels as the TAP driver is currently implemented, therefor OpenVPN emulates this by using a /30 (255.255.255.252) subnet.

I'm lost here. When doing p2p (with 1.6 or 2.0) I get .4.0, .4.2 and .4.255 in the routing table. Where can I read up on this? I should probably do some googling on routing, 'cause I still don't quite get it.

I don't think it's very well documented. The man page has some basic info about it on the --ifconfig-pool option. Basically when you use this option (with dev tun), the server takes the first /30 subnet, and the following subnets are assigned to clients.


There was an in-depth discussion about this a few months ago here on the list though, so you might find some interesting info if you search the archive.

When you are assigned IP address 192.168.4.6, .5 is your gateway. .1 is OpenVPN's IP address yes, but not on the /30 subnet that has been assigned to you.

I tried out --redirect-gateway, but that added 192.168.4.5 as the default gw, which obviously did't work.

That's what it should do.

Bloody silly me. I could not ping 192.168.4.5, so I never bothered to look beyond the firewall. It was blocking outbound traffic from .4.0. Everything works now. You've helped me a great deal (I've spent the weekend looking into this :-))

Yes, I find this a little odd too. I don't remember the rational behind why ping's are not replied to on this address, but I'm sure James has some good explaination for this!


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