On 20. Oct 2020, at 23:11, Marcelo Ricardo Leitner [off-list ref] wrote:

On Tue, Oct 20, 2020 at 05:12:06PM +0800, Xin Long wrote:

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On Tue, Oct 20, 2020 at 6:15 AM Marcelo Ricardo Leitner
[off-list ref] wrote:

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On Mon, Oct 19, 2020 at 08:25:33PM +0800, Xin Long wrote:

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--- 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.

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+     The listening port for the local UDP tunneling sock.

       , shared by all applications in the same net namespace.

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+     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.

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+
+     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)

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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.

Best regards
Michael