Re: [PATCH] openvpn: Actually apply configured parameters

[Michael Tremer <michael.tremer@ipfire.org>]

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Hello,

I didn’t merge this yet, because I did not get any testing feedback (with a Tested-by tag).

Since nobody has anything to complain, I will merge it then.

Best,
-Michael

> On 24 Nov 2020, at 15:19, ummeegge <ummeegge(a)ipfire.org> wrote:
> 
> Hi Michael,
> wanted to warm this up alittle :-) do you want to deliver this patch ?
> 
> Best,
> 
> Erik
> 
> Am Dienstag, den 20.10.2020, 13:28 +0000 schrieb Michael Tremer:
>> OpenVPN is an absolute mess. The behaviour of configuration
>> parameters has been changed over the time; default values have been
>> changed over time; and it looks like nobody is actually testing
>> anything any more.
>> 
>> I have been spending hours today on figuring out why OpenVPN
>> is so damn slow. On a Lightning Wire Labs IPFire Mini Appliance
>> it achieves about 100 MBit/s in the default configuration when
>> "openssl speed -evp aes-256-gcm" achieves over 3.5 GBit/s.
>> 
>> Changing any of the cryptography parameters does not change
>> anything. Throughput remains around 100 MBit/s.
>> 
>> I finally set "cipher none" and "auth none" which disables
>> encryption and authentication altogether but does not increase
>> throughput. From here on it was absolutely clear that it was
>> not a crypto issue.
>> 
>> OpenVPN tries to be smart here and does its own fragmentation.
>> This is the worst idea I have heard of all day, because that job
>> is normally done best by the OS.
>> 
>> Various settings which allow the user to "tune" this are grossly
>> ineffective - let alone it isn't even clear what I am supposed
>> to configure anywhere. Setting "fragment 1500" weirdly still
>> does not convince openvpn to generate a packet that is longer
>> than 1400 bytes. Who'd a thunk?
>> 
>> There is a number of other parameters to set the MTU or which
>> are related to it (tun-mtu, link-mtu, fragment, mssfix).
>> 
>> On top of all of this we have two "bugs" in ovpnmain.cgi which
>> are being fixed in this patch:
>> 
>> 1) mssfix can be configured by the user. However, we always
>>    enable it in openvpn. The default is on, we only add "mssfix"
>>    which simply turns it on.
>>    It is now being disabled when the user has chosen so in the
>>    web UI. I do not know if this is backwards-compatible.
>> 
>> 2) We cap the MTU (tun-mtu) at 1500 bytes when fragment is being
>>    used. So it becomes pointless that the user can this and the
>>    user is not being made aware of this when they hit the save
>>    button.
>>    This was added when we added path MTU discovery. Since that
>>    did not work and was removed, we can remove this now, too.
>> 
>> I archived a solid 500-600 MBit/s of goodput with these settings:
>> 
>> * Disable mssfix
>> * Set "fragment" to 0
>> * Set MTU to 9000
>> 
>> I am sure the MTU could be further increased to have bigger packets,
>> but I did not test how badly this will affect latency of the tunnel.
>> 
>> OpenVPN seems to only be able to handle a certain amount of packets
>> a second - no matter what. With larger packets, the throughput of
>> the tunnel increases, but latency might as well.
>> 
>> Signed-off-by: Michael Tremer <michael.tremer(a)ipfire.org>
>> Cc: Erik Kapfer <erik.kapfer(a)ipfire.org>
>> Cc: Stefan Schantl <stefan.schantl(a)ipfire.org>
>> ---
>>  html/cgi-bin/ovpnmain.cgi | 29 +++++++++--------------------
>>  1 file changed, 9 insertions(+), 20 deletions(-)
>> 
>> diff --git a/html/cgi-bin/ovpnmain.cgi b/html/cgi-bin/ovpnmain.cgi
>> index e7bc505e7..e5bc45c1c 100644
>> --- a/html/cgi-bin/ovpnmain.cgi
>> +++ b/html/cgi-bin/ovpnmain.cgi
>> @@ -280,14 +280,7 @@ sub writeserverconf {
>>      print CONF "server $tempovpnsubnet[0] $tempovpnsubnet[1]\n";
>>      #print CONF "push \"route $netsettings{'GREEN_NETADDRESS'}
>> $netsettings{'GREEN_NETMASK'}\"\n";
>>  
>> -    # Check if we are using mssfix, fragment and set the corretct
>> mtu of 1500.
>> -    # If we doesn't use one of them, we can use the configured mtu
>> value.
>> -    if ($sovpnsettings{'MSSFIX'} eq 'on') 
>> -       { print CONF "tun-mtu 1500\n"; }
>> -    elsif ($sovpnsettings{'FRAGMENT'} ne '' &&
>> $sovpnsettings{'DPROTOCOL'} ne 'tcp') 
>> -       { print CONF "tun-mtu 1500\n"; }
>> -    else 
>> -       { print CONF "tun-mtu $sovpnsettings{'DMTU'}\n"; }
>> +    print CONF "tun-mtu $sovpnsettings{'DMTU'}\n";
>>  
>>      if ($vpnsettings{'ROUTES_PUSH'} ne '') {
>>                 @temp = split(/\n/,$vpnsettings{'ROUTES_PUSH'});
>> @@ -320,6 +313,8 @@ sub writeserverconf {
>>      }
>>      if ($sovpnsettings{MSSFIX} eq 'on') {
>>                 print CONF "mssfix\n";
>> +    } else {
>> +               print CONF "mssfix 0\n";
>>      }
>>      if ($sovpnsettings{FRAGMENT} ne '' &&
>> $sovpnsettings{'DPROTOCOL'} ne 'tcp') {
>>                 print CONF "fragment $sovpnsettings{'FRAGMENT'}\n";
>> @@ -975,7 +970,7 @@ unless(-d
>> "${General::swroot}/ovpn/n2nconf/$cgiparams{'NAME'}"){mkdir
>> "${General
>>    if ($cgiparams{'MTU'} eq '') {$tunmtu = '1500'} else {$tunmtu =
>> $cgiparams{'MTU'}};
>>    print SERVERCONF "tun-mtu $tunmtu\n";
>>    if ($cgiparams{'FRAGMENT'} ne '') {print SERVERCONF "fragment
>> $cgiparams{'FRAGMENT'}\n";} 
>> -  if ($cgiparams{'MSSFIX'} eq 'on') {print SERVERCONF "mssfix\n"; };
>> +  if ($cgiparams{'MSSFIX'} eq 'on') {print SERVERCONF "mssfix\n"; }
>> else { print SERVERCONF "mssfix 0\n" };
>>    }
>>  
>>    print SERVERCONF "# Auth. Server\n"; 
>> @@ -1074,7 +1069,7 @@ unless(-d
>> "${General::swroot}/ovpn/n2nconf/$cgiparams{'NAME'}"){mkdir
>> "${General
>>    if ($cgiparams{'MTU'} eq '') {$tunmtu = '1500'} else {$tunmtu =
>> $cgiparams{'MTU'}};
>>    print CLIENTCONF "tun-mtu $tunmtu\n";
>>    if ($cgiparams{'FRAGMENT'} ne '') {print CLIENTCONF "fragment
>> $cgiparams{'FRAGMENT'}\n";}
>> -  if ($cgiparams{'MSSFIX'} eq 'on') {print CLIENTCONF "mssfix\n"; };
>> +  if ($cgiparams{'MSSFIX'} eq 'on') {print CLIENTCONF "mssfix\n"; }
>> else { print CLIENTCONF "mssfix 0\n" };
>>    }
>>  
>>    # Check host certificate if X509 is RFC3280 compliant.
>> @@ -2204,7 +2199,7 @@ if ($confighash{$cgiparams{'KEY'}}[3] eq
>> 'net'){
>>     if ($confighash{$cgiparams{'KEY'}}[31] eq '') {$tunmtu = '1500'}
>> else {$tunmtu = $confighash{$cgiparams{'KEY'}}[31]};
>>     print CLIENTCONF "tun-mtu $tunmtu\n";
>>     if ($confighash{$cgiparams{'KEY'}}[24] ne '') {print CLIENTCONF
>> "fragment $confighash{$cgiparams{'KEY'}}[24]\n";}
>> -   if ($confighash{$cgiparams{'KEY'}}[23] eq 'on') {print CLIENTCONF
>> "mssfix\n";}
>> +   if ($confighash{$cgiparams{'KEY'}}[23] eq 'on') {print CLIENTCONF
>> "mssfix\n";} else { print CLIENTCONF "mssfix 0\n"; }
>>     }
>>     # Check host certificate if X509 is RFC3280 compliant.
>>     # If not, old --ns-cert-type directive will be used.
>> @@ -2285,15 +2280,7 @@ else
>>      print CLIENTCONF "nobind\r\n";
>>      print CLIENTCONF "dev tun\r\n";
>>      print CLIENTCONF "proto $vpnsettings{'DPROTOCOL'}\r\n";
>> -
>> -    # Check if we are using fragment, mssfix and set MTU to 1500
>> -    # or use configured value.
>> -    if ($vpnsettings{FRAGMENT} ne '' && $vpnsettings{DPROTOCOL} ne
>> 'tcp' )
>> -       { print CLIENTCONF "tun-mtu 1500\r\n"; }
>> -    elsif ($vpnsettings{MSSFIX} eq 'on')
>> -       { print CLIENTCONF "tun-mtu 1500\r\n"; }
>> -    else
>> -       { print CLIENTCONF "tun-mtu $vpnsettings{'DMTU'}\r\n"; }
>> +    print CLIENTCONF "tun-mtu $vpnsettings{'DMTU'}\r\n";
>>  
>>      if ( $vpnsettings{'ENABLED'} eq 'on'){
>>         print CLIENTCONF "remote $vpnsettings{'VPN_IP'}
>> $vpnsettings{'DDEST_PORT'}\r\n";
>> @@ -2383,6 +2370,8 @@ else
>>      print CLIENTCONF "verify-x509-name
>> $vpnsettings{ROOTCERT_HOSTNAME} name\r\n";
>>      if ($vpnsettings{MSSFIX} eq 'on') {
>>         print CLIENTCONF "mssfix\r\n";
>> +    } else {
>> +       print CLIENTCONF "mssfix 0\r\n";
>>      }
>>      if ($vpnsettings{FRAGMENT} ne '' && $vpnsettings{DPROTOCOL} ne
>> 'tcp' ) {
>>         print CLIENTCONF "fragment $vpnsettings{'FRAGMENT'}\r\n";
> 
>