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    SubjectRe: [PATCH net-next 2/2 v2] firewire: net: set initial MTU = 1500 unconditionally, fix IPv6 on some CardBus cards
    On Mon, Oct 24, 2016 at 02:26:13PM +0200, Stefan Richter wrote:
    > firewire-net, like the older eth1394 driver, reduced the initial MTU to
    > less than 1500 octets if the local link layer controller's asynchronous
    > packet reception limit was lower.
    >
    > This is bogus, since this reception limit does not have anything to do
    > with the transmission limit. Neither did this reduction affect the TX
    > path positively, nor could it prevent link fragmentation at the RX path.
    >
    > Many FireWire CardBus cards have a max_rec of 9, causing an initial MTU
    > of 1024 - 16 = 1008. RFC 2734 and RFC 3146 allow a minimum max_rec = 8,
    > which would result in an initial MTU of 512 - 16 = 496. On such cards,
    > IPv6 could only be employed if the MTU was manually increased to 1280 or
    > more, i.e. IPv6 would not work without intervention from userland.
    >
    > We now always initialize the MTU to 1500, which is the default according
    > to RFC 2734 and RFC 3146.
    >
    > On a VIA VT6316 based CardBus card which was affected by this, changing
    > the MTU from 1008 to 1500 also increases TX bandwidth by 6 %.
    > RX remains unaffected.
    >
    > CC: netdev@vger.kernel.org
    > CC: linux1394-devel@lists.sourceforge.net
    > CC: Jarod Wilson <jarod@redhat.com>
    > Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
    > ---
    > v2: use ETH_DATA_LEN, add comment

    Acked-by: Jarod Wilson <jarod@redhat.com>

    --
    Jarod Wilson
    jarod@redhat.com

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