On Sun, Feb 17, 2019 at 02:25:17PM +0000, Russell King wrote: > Switches work by learning the MAC address for each attached station by > monitoring traffic from each station. When a station sends a packet, > the switch records which port the MAC address is connected to. > > With IPv4 networking, before communication commences with a neighbour, > an ARP packet is broadcasted to all stations asking for the MAC address > corresponding with the IPv4. The desired station responds with an ARP > reply, and the ARP reply causes the switch to learn which port the > station is connected to. > > With IPv6 networking, the situation is rather different. Rather than > broadcasting ARP packets, a "neighbour solicitation" is multicasted > rather than broadcasted. This multicast needs to reach the intended > station in order for the neighbour to be discovered. > > Once a neighbour has been discovered, and entered into the sending > stations neighbour cache, communication can restart at a point later > without sending a new neighbour solicitation, even if the entry in > the neighbour cache is marked as stale. This can be after the MAC > address has expired from the forwarding cache of the DSA switch - > when that occurs, there is a long pause in communication. > > Our DSA implementation for mv88e6xxx switches has defaulted to having > multicast and unicast flooding disabled. As per the above description, > this is fine for IPv4 networking, since the broadcasted ARP queries > will be sent to and received by all stations on the same network. > However, this breaks IPv6 very badly - blocking neighbour solicitations > and later causing connections to stall. > > The defaults that the Linux bridge code expect from bridges are that > unknown unicast frames and unknown multicast frames are flooded to > all stations, which is at odds to the defaults adopted by our DSA > implementation for mv88e6xxx switches. > > This commit enables by default flooding of both unknown unicast and > unknown multicast frames. This means that mv88e6xxx DSA switches now > behave as per the bridge(8) man page, and IPv6 works flawlessly through > such a switch.
Note that there is the open question whether this affects the case where each port is used as a separate network interface: that case has not yet been tested. > > Signed-off-by: Russell King <[email protected]> > --- > drivers/net/dsa/mv88e6xxx/chip.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/dsa/mv88e6xxx/chip.c > b/drivers/net/dsa/mv88e6xxx/chip.c > index b75a865a293d..eb5e3d88374f 100644 > --- a/drivers/net/dsa/mv88e6xxx/chip.c > +++ b/drivers/net/dsa/mv88e6xxx/chip.c > @@ -2144,13 +2144,14 @@ static int mv88e6xxx_setup_message_port(struct > mv88e6xxx_chip *chip, int port) > static int mv88e6xxx_setup_egress_floods(struct mv88e6xxx_chip *chip, int > port) > { > struct dsa_switch *ds = chip->ds; > - bool flood; > > - /* Upstream ports flood frames with unknown unicast or multicast DA */ > - flood = dsa_is_cpu_port(ds, port) || dsa_is_dsa_port(ds, port); > + /* Linux bridges are expected to flood unknown multicast and > + * unicast frames to all ports - as per the defaults specified > + * in the iproute2 bridge(8) man page. Not doing this causes > + * stalls and failures with IPv6 over Marvell bridges. */ > if (chip->info->ops->port_set_egress_floods) > return chip->info->ops->port_set_egress_floods(chip, port, > - flood, flood); > + true, true); > > return 0; > } > -- > 2.7.4 > > -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up
