netdev - Re: RMNET QMAP data aggregation with size greater than 16384

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Date:   Thu, 05 Aug 2021 16:57:00 -0600
From:   subashab@...eaurora.org
To:     Aleksander Morgado <aleksander@...ksander.es>
Cc:     Bjørn Mork <bjorn@...k.no>,
        Daniele Palmas <dnlplm@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        stranche@...eaurora.org
Subject: Re: RMNET QMAP data aggregation with size greater than 16384

> I may be mistaken then in how this should be setup when using rmnet.
> For the qmi_wwan case using add_mux/del_mux (Daniele correct me if
> wrong!), we do need to configure the MTU of the master interface to be
> equal to the aggregation data size reported via QMI WDA before
> creating any mux link; see
> http://paldan.altervista.org/linux-qmap-qmi_wwan-multiple-pdn-setup/
> 
> I ended up doing the same here for the rmnet case; but if it's not
> needed I can definitely change that. I do recall that I originally had
> left the master MTU untouched in the rmnet case and users had issues,
> and increasing it to the aggregation size solved that; I assume that's
> because the MTU should have been increased to accommodate the extra
> MAP header as you said. How much more size does it need on top of the
> 1500 bytes?

You need to use an additional 4 bytes for MAPv1 and 8 bytes for 
MAPv4/v5.

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