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On 21/05/15 14:25, Josu Lazkano wrote:
> 2015-05-20 23:49 GMT+02:00 David Sommerseth
> <openvpn.l...@topphemmelig.net>:
[...snip...]
>> 
>> I'll admit I haven't paid attention to all details in this
>> discussion. Static encrypted VPN tunnels can work very well, but
>> I just want to emphasize one security aspect of static encrypted
>> VPN tunnels.  This configuration will not give you PFS (Perfect
>> Forward Secrecy).  That means that if someone saves all your VPN
>> traffic and either manages to bruteforce the encryption key or
>> manags to get a copy of your static encryption key, all the saved
>> traffic can be decrypted.
>> 
>> That is one of the key reasons it is adviseable to use the TLS
>> mode with client/server certificates.  Using this method, the
>> encryption keys used for the VPN tunnel are negotiated upon
>> connection *and* can be renegotiated after a certain time
>> (default is every hour, but you can modify that and add
>> renegotiation after X number of network packets and/or Y
>> transferred bytes).  This provides a very good protection when it
>> comes replay attaks and it provides PFS.  TLS mode also adds
>> possibility to further protect you against MITM attacks from
>> unkown attackers, using --tls-auth.  The --tls-auth feature has
>> also proved to be a very good protection against many OpenSSL
>> bugs as well.  If you combine UDP with --tls-auth, the OpenVPN
>> server port will also be hidden for port scanners.
>> 
>> If these things are not of any concern to you, then static
>> tunnels can indeed be a good alternative.
>> 
>> 
>> kind regards,
>> 
>> David Sommerseth
> 
> Thanks David,
> 
> I started with static key just to start with a simple
> configuration. Now I want to secure my connection, would it work
> just adding "--tls-auth" option?

It's not that easy, unfortunately.  And you've already been down that
path once already.

To switch to TLS mode, you need to use --ca, --cert and --key.  In
addition on the server side you need --dh as well.  This means you
need to have a CA where you issue certificates.

In addition, you're back to the need to use --client-config-dir and
- --iroute as well to make LAN-to-LAN-over-VPN work.

And then you can add --tls-auth as well, on top of all of this.

[...snip...]
> 
> Both networks have 30mbps/3mbps WAN connection, I want to secure
> my VPN link and have a good latency, is this possible? Which is the
> best configuration for this?

- From my experiences with VPNs, there are no "silver bullet" config
file which works optimal for everyone.  How your ISPs handles your VPN
traffic can impact this a lot.  Some networks I had to use TCP instead
of the preferred UDP.  Some places I needed to tweak MTU settings to
have a reliable tunnel.  Once I even had to tunnel a TCP connection
through obfsproxy to be able to have a functional tunnel (despite
traffic not being blocked by a "great firewall").  So, it is close to
impossible to say "do this and it will perform optimal".  You need to
try different things yourself and see what works for you.

I suggest you grab a copy of the "OpenVPN 2 Cookbook" [1] and read
this wiki carefully:
<https://community.openvpn.net/openvpn/wiki/Gigabit_Networks_Linux>

With these resources, you'll get a long way.

[1] <http://shop.oreilly.com/product/9781849510103.do>


- -- 
kind regards,

David Sommerseth
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