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

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Date:   Wed, 21 Oct 2020 11:13:41 +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 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?

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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