Re: [PATCH] openvpn: Actually apply configured parameters

[ummeegge <ummeegge@ipfire.org>]

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Hi Michael,

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
We have had a discussion about that longer time ago -->
https://bugzilla.ipfire.org/show_bug.cgi?id=11364#c18
. Did not know that a MTU of 9000 is possible, sounds like jumbo
frames.

> 
> 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";