netdev - Re: [PATCHv4 net-next 16/16] sctp: enable udp tunneling socks

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Message-Id: <EC95E629-CB0D-463A-99B3-5C474D4DD3F3@fh-muenster.de>
Date:   Thu, 22 Oct 2020 13:38:38 +0200
From:   Michael Tuexen <tuexen@...muenster.de>
To:     Xin Long <lucien.xin@...il.com>
Cc:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        network dev <netdev@...r.kernel.org>,
        linux-sctp@...r.kernel.org, Neil Horman <nhorman@...driver.com>,
        davem <davem@...emloft.net>, Guillaume Nault <gnault@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCHv4 net-next 16/16] sctp: enable udp tunneling socks

`On 22. Oct 2020, at 05:12, Xin Long <lucien.xin@...il.com> wrote:
> 
> On Wed, Oct 21, 2020 at 5:13 PM Michael Tuexen <tuexen@...muenster.de> wrote:
>> 
>>> On 21. Oct 2020, at 06:16, Xin Long <lucien.xin@...il.com> wrote:
>>> 
>>> On Wed, Oct 21, 2020 at 5:23 AM Marcelo Ricardo Leitner
>>> <marcelo.leitner@...il.com> wrote:
>>>> 
>>>> On Tue, Oct 20, 2020 at 11:15:26PM +0200, Michael Tuexen wrote:
>>>>>> On 20. Oct 2020, at 23:11, Marcelo Ricardo Leitner <marcelo.leitner@...il.com> wrote:
>>>>>> 
>>>>>> On Tue, Oct 20, 2020 at 05:12:06PM +0800, Xin Long wrote:
>>>>>>> On Tue, Oct 20, 2020 at 6:15 AM Marcelo Ricardo Leitner
>>>>>>> <marcelo.leitner@...il.com> wrote:
>>>>>>>> 
>>>>>>>> On Mon, Oct 19, 2020 at 08:25:33PM +0800, Xin Long wrote:
>>>>>>>>> --- a/Documentation/networking/ip-sysctl.rst
>>>>>>>>> +++ b/Documentation/networking/ip-sysctl.rst
>>>>>>>>> @@ -2640,6 +2640,12 @@ addr_scope_policy - INTEGER
>>>>>>>>> 
>>>>>>>>>    Default: 1
>>>>>>>>> 
>>>>>>>>> +udp_port - INTEGER
>>>>>>>> 
>>>>>>>> Need to be more verbose here, and also mention the RFC.
>>>>>>>> 
>>>>>>>>> +     The listening port for the local UDP tunneling sock.
>>>>>>>>      , shared by all applications in the same net namespace.
>>>>>>>>> +     UDP encapsulation will be disabled when it's set to 0.
>>>>>>>> 
>>>>>>>>      "Note, however, that setting just this is not enough to actually
>>>>>>>>      use it. ..."
>>>>>>> When it's a client, yes,  but when it's a server, the encap_port can
>>>>>>> be got from the incoming packet.
>>>>>>> 
>>>>>>>> 
>>>>>>>>> +
>>>>>>>>> +     Default: 9899
>>>>>>>>> +
>>>>>>>>> encap_port - INTEGER
>>>>>>>>>    The default remote UDP encapsalution port.
>>>>>>>>>    When UDP tunneling is enabled, this global value is used to set
>>>>>>>> 
>>>>>>>> When is it enabled, which conditions are needed? Maybe it can be
>>>>>>>> explained only in the one above.
>>>>>>> Thanks!
>>>>>>> pls check if this one will be better:
>>>>>> 
>>>>>> It is. Verbose enough now, thx.
>>>>>> (one other comment below)
>>>>>> 
>>>>>>> 
>>>>>>> udp_port - INTEGER
>>>>>>> 
>>>>>>> The listening port for the local UDP tunneling sock.
>>>>>>> 
>>>>>>> This UDP sock is used for processing the incoming UDP-encapsulated
>>>>>>> SCTP packets (from RFC6951), and shared by all applications in the
>>>>>>> same net namespace. This UDP sock will be closed when the value is
>>>>>>> set to 0.
>>>>>>> 
>>>>>>> The value will also be used to set the src port of the UDP header
>>>>>>> for the outgoing UDP-encapsulated SCTP packets. For the dest port,
>>>>>>> please refer to 'encap_port' below.
>>>>>>> 
>>>>>>> Default: 9899
>>>>>> 
>>>>>> I'm now wondering if this is the right default. I mean, it is the
>>>>>> standard port for it, yes, but at the same time, it means loading SCTP
>>>>>> module will steal/use that UDP port on all net namespaces and can lead
>>>>>> to conflicts with other apps. A more conservative approach here is to
>>>>>> document the standard port, but set the default to 0 and require the
>>>>>> user to set it in if it is expected to be used.
>>>>>> 
>>>>>> Did FreeBSD enable it by default too?
>>>>> No. The default is 0, which means that the encapsulation is turned off.
>>>>> Setting this sysctl variable to a non-zero value enables the UDP tunneling
>>>>> with the given port.
>>>> 
>>>> Thanks Michael.
>>>> Xin, then we should change this default value (and update the
>>>> documentation above accordingly, to still have the standard port #
>>>> readily available in there).
>>> OK, I misunderstood the RFC.
>> Does that RFC mandate that the feature is on by default? Can you point me to
>> that text?
> Not really.
> 
> I was thinking that by leaving it to 9899 by default users don't need to
> know the port when want to use it, and yet I didn't want to add another
> sysctl member. :D
OK. Thanks for letting me know.

Best regards
Michael
> 
>> 
>> Best regards
>> Michael
>>> 
>>> I will remove the call to sctp_udp_sock_start/stop() from
>>> sctp_ctrlsock_init/exit(), and set the udp_port as 0 by default.
>>> 
>>> Thanks.
>> 


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