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Old 04-04-2012, 06:09 PM   #1
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Registered: Mar 2011
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Need aid understanding -> Centos 6 VPS, VPN, PPTP, DD-WRT


I have a DD-WRT router that can only do PPTP (it might be able to do openvpn if I flash it with a different firmware but I want to just try to get this working first if possible).

I have a remote VPS that I can SSH into a root shell.

I'm trying to get my head around this whole thing:

a VPN is software that lets you tunnel from one network into another so that you can access that network as if you were locally connected.

I should be able to install software on a VPS to give it this ability. As always, there are different 'products' (probably the wrong term) that do this. For example: PPTP is one and uses something called MPPE for its encryption whereas OpenVPN is another (and from what I read, preferred) and uses IPSec for it's encryption. My router can only handle PPTP at the moment so I want to start with that if it's neither here nor there.

So what I need to do is configure the VPN PPTP client on my dd-wrt router (some of those settings are confusing me) and install, configure and run this PPTP VPN on the remote linux (Centos 6) VPS.

The VPS I am using is from AlienVPS. It's their cheapest one that's something like $19 for the entire year. I had better ones before when I was hosting a minecraft and terraria server but I paid for this one at first and forgot about it and then the other night I remembered I had it so I wanted to start with this.

My first concern is that I don't know how to find my subnet.
Well, first of all, my VPN page on my router looks like this:

and here's the documentation from my router's help page:

I'm not sure if the MPPE setting is okay but before I can even get to that point, I'm confused about the subnet. It has two fields: remote subnet and remote subnet masking.

I googled to try to figure out how to determine this from my VPS and got this site:

The site says my ifconfig should give me the following information:

lnc0: flags=108843 mtu 1500
        inet netmask 0xfffffff8 broadcast
        ether 00:0c:29:32:8a:8c
plip0: flags=108810 mtu 1500
lo0: flags=8049 mtu 16384
        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
        inet6 ::1 prefixlen 128
        inet netmask 0xff000000
but I see:
lo        Link encap:Local Loopback  
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:391 errors:0 dropped:0 overruns:0 frame:0
          TX packets:391 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:32430 (31.6 KiB)  TX bytes:32430 (31.6 KiB)

venet0    Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:  P-t-P:  Bcast:  Mask:
          RX packets:492739 errors:0 dropped:0 overruns:0 frame:0
          TX packets:559062 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:60697942 (57.8 MiB)  TX bytes:95244391 (90.8 MiB)

venet0:0  Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:123.456.789.101  P-t-P:123.456.789.101  Bcast:123.456.789.101  Mask:
p.s. I'm not sure if any of that information in what I see is dangerous to make public. Please let me know if I shouldn't have posted anything. I have changed the IP address but other than that I don't know if anything is dangerous.

Anyway, I do not see a 'net mask' field, which was supposed to represent my subnet mask. Is my subnet and my subnet mask

Also, my MTU is 16436…should I put that in the router too?

Then I need to install a PPTP VPN on the VPS. I'm not sure how to do that yet, I just wanted to clear up these settings first.

Thanks for any advice.
Old 04-04-2012, 06:16 PM   #2
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Registered: Mar 2011
Posts: 7

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makes me think that my subnet is, which doesn't make sense since that's the local home address (self address).

What the user posts on that page shows a eth0 adapter with a inet addr of which would be his subnet.

But on mine it's either (which doesn't make sense to me) if I'm looking at the venet0 adapter or, as in the case of the venet0:0 adapter, it's the same as my external ip address.

I'm thinking about what this it because the computer is directly connected to the internet (virtually, it doesn't run through a router) or is it because linux requires I have some kind of VPN software (PPTP?) installed first before it even has a subnet?

Last edited by Aro2220; 04-04-2012 at 06:20 PM.


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