Re: test of lzo option in OpenVPN

[Adolf Belka <adolf.belka@ipfire.org>]

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Hi Michael,

On 05/09/2023 18:30, Michael Tremer wrote:
> Hello Adolf,
> 
> Thank you for checking this one out.
> 
>> On 4 Sep 2023, at 21:15, Adolf Belka <adolf.belka(a)ipfire.org> wrote:
>>
>> Hi All,
>>
>> On 04/09/2023 21:51, Adolf Belka wrote:
>>> Hi All,
>>>
>>> As discussed in the conf call I did a test of the LZO option and the result was not what I had hoped for, at least with Network Manager - openvpn plugin.
>>>
>>> Using my vm testbed, I created a client with LZO option enabled.
>>>
>>> I made an opnvpn connection which was successful and worked.
>>>
>>> Then I disabled LZO on the server but left the client as it was.
>>>
>>> Remade the connection. The connection showed as CONNECTED in the openvpn WUI page but in my Arch Linux log for the network manager I got a periodic message of
>>>
>>> nm-openvpn[1266]: Bad LZO decompression header byte: 42
>>>
>>> Additionally trying to use the browser through the tunnel failed with the web sites timing out.
>>>
>>> So at least with Network Manager Openvpn plugin turning LZO off on the server ,when the client has it specified, does not work the way we discussed.
>>>
>>> I will do a further test with openvpn directly on the command line but if one openvpn client doesn't accept LZO being turned off on the server if it is enabled in the client this means we can't remove the LZO option and default it to disabled on the WUI page.
>>>
>> The same problem occurs when using openvpn as a client from the command line. LZO on the client and server works fine or both disabled works fine but lzo on client but turned off on server gives the same error message as found with network manager - openvpn plugin and although the Status shows as CONNECTED no traffic is successfully passed due to the compression mismatch.
>>
>> Conclusion: we can't remove the LZO option from the WUI page and have it default to off for everyone.
> 
> This is sad, but I think we already anticipated this.
> 
> I am now wondering what will happen when this option gets removed upstream (https://community.openvpn.net/openvpn/wiki/DeprecatedOptions#Option:--comp-lzoStatus:Pendingremoval). It hasn’t been decided, yet, but it is at least deprecated and already does not actually enable any compression.
> 
> That being said, we should remove the checkbox anyway then, because the page says:
> 
>    Beginning with 2.5, these options will no longer enable compression, just enable the compression framing to be able to receive compressed packets.
> 
> So it is misleading to users right now because there is no compression whatsoever, it just enables an extra header which wastes space.
> 
> It should not be possible to enable this on new installations.
I see what you are suggesting. We remove the checkbox in the iso and 
image files.

What we could also do is that in the next update we check if the server 
has LZO enabled and if not then the checkbox is removed on systems not 
using it.

That then leaves the people with the LZO checkbox enabled.
I would suggest that I create a patch that places a warning message in 
red on the main OpenVPN WUI page that warns that the LZO option is not 
compressing since version 2.5.0 and that the option has been deprecated 
and will be removed by OpenVPN at some time in the future and requesting 
IPFire users to update their clients to remove the LZO option.

I should also test out what happens if the LZO option is enabled on the 
server but removed on the client. Does that also break the connection. 
The answer will probably be yes which will mean that IPFire admins will 
need to change all clients and the server at the same time.

Regards,

Adolf.
> 
> What do we do with this chaos now?
> 
> -Michael
> 
>>
>> Regards,
>>
>> Adolf.
>>
>>> Regards,
>>>
>>> Adolf.
>>>
>>
>> -- 
>> Sent from my laptop
> 
> 

-- 
Sent from my laptop