Regression regarding ip_type when updating from 1.10.4 to 1.12.0

[Dan Williams]

On Fri, 2019-11-15 at 10:33 +0100, Aleksander Morgado wrote:
> Hey,
> 
> > > On Thu, Nov 14, 2019 at 06:57:54PM +0100, Aleksander Morgado
> > > wrote:
> > > > > Has the interpretation of the ip_type
> > > > > MM_BEARER_IP_FAMILY_IPV4V6
> > > > > changed when performing the connect?
> > > > > 
> > > > 
> > > > No it hasn't really. I really think you need to know whether
> > > > the
> > > > network supports ipv4v6 for a given APN before attempting to
> > > > use
> > > > it.
> > > 
> > > For writing end user oriented software where the networks and
> > > operators
> > > that will be used are unknown when implementing it this becomes a
> > > big
> > > problem.
> > 
> > I'm not sure I see how. If you pass MM_BEARER_IP_FAMILY_ANY then
> > you
> > will get some kind of connectivity, most often V4 because that's
> > what
> > most networks provide.
> > 
> > If you pass V4, V6, or V4V6 then MM will fail if the network cannot
> > provide that connectivity. Presumably you are passing these options
> > because you require the connectivity each one provides, otherwise
> > if
> > all you care about is "can I get to the Internet" you could pass
> > ANY.
> > 
> > > Wouldn't that mean one has to try a connect with all bearer types
> > > in
> > > whatever the preferred order is?
> > 
> > Or pass ANY and you'll get some kind of connection to the internet
> > at
> > least?
> > 
> > Aleksander: we should probably fine-tune the logic something like
> > this:
> > 
> > 1) bearer default_ip_family follows what the modem is capable of
> > via
> > AT+CGDCONT=? or the equivalent; eg if the modem has V4V6 contexts
> > then
> > we default to IPV4V6.
> 
> The "default IP family" is IPv4 for all modems, there's no +CGDCONT=?
> check changing that.
> 
> The +CGDCONT=? check helps build the "supported IP families" list
> that
> we expose in the Modem interface when the device uses AT protocol.
> For
> MBIM and QMI modems, the list of supported IP families includes all
> IPv4, IPv6 and IPv4v6.
> 
> > 2) If the user passes a specific IP family for the bearer, fail if
> > that
> > family is not successfully connected (as we do now?)
> 
> More or less. If user asks for IPv4 or IPv6 and that fails, we fail
> always regardless of the modem type.
> 
> In QMI modems, where we control the IPv4 and IPv6 setups separately
> via different QMI clients, if the user asks for IPv4v6 and any of
> them
> succeeds, we succeed. So if user asks for IPv4v6 and we get IPv4
> only,
> we would not trigger an error. Maybe we should? It's definitely
> easier
> for us to just succeed here, because otherwise it would mean that if
> IPv6 setup fails we would need to then disconnect the IPv4 setup
> manually before reporting the connection error.
> 
> For other modems (AT or MBIM) there is one single command requesting
> IPv4v6 and that is left to the modem to decide whether the connection
> command succeeds or not. This is the key point I believe. If we
> default ANY to IPv4v6 and we ask IPv4v6 by default when no explicit
> ip-type provided, and the modem decides to fail the connection if we
> can only setup IPv4, wouldn't that be a very bad thing?
> 
> > 3) If the user passes ANY:
> >   3a) use the default_ip_family (no change)
> 
> That is what we're doing right now, but because default IP family is
> IPv4, we fallback to IPv4.

Well, there's no fallback, passing ANY always means V4 because
default_ip_family is hardcoded to V4 AFAICT.

> >   3b) the modem accepts whatever connect result happens, eg if v4
> > or
> > v6-only that's fine, don't fail.
> >   3c) if the connection result failed because the network rejected
> > a
> > V4V6 request for example, or the default_ip_family is V4 but the
> > APN
> > only accepts V6, then should we retry with V4?
> 
> Are you suggesting we improve the ANY handling in order to attempt
> different IP type connections automatically if they fail? E.g. if the
> user asks for ANY, try first with IPv4v6 and if anything succeeds
> we're good. If it fails, try with IPv4-only, and if it fails, try
> with
> IPv6. That would make the ANY name much more meaningful actually.

Yes, basically :) But I'm also suggesting that we change
default_ip_family to something other than V4 when the modem supports
it. eg maybe we set it to V4V6 and if one of the V4 or V6 methods fails
we just proceed with single-stack connectivity?

But the user explicitly requests V4V6 type we fail if we don't get both
v4 and v6.

Dan