On Tue, Feb 19, 2019 at 11:05:37AM -0500, Vivien Didelot wrote: > Hi Russell, > > On Mon, 18 Feb 2019 12:53:45 +0000, Russell King - ARM Linux admin > <li...@armlinux.org.uk> wrote: > > On Sun, Feb 17, 2019 at 04:32:40PM +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. > > Thank you for the very informative message above. > > > > 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. > > > > Thinking about this a bit more, this approach probably isn't the best. > > If we have a port that goes through this life-cycle: > > > > 1. assigned to a bridge > > 2. configured not to flood > > 3. reassigned to a new bridge > > > > the port will retain its settings from the first bridge, which will be > > at odds with the settings that the Linux bridge code expects and the > > settings visible to the user. > > > > So, how about this, which basically reverts this patch and applies the > > flood settings each time a port joins a bridge, and clears them when > > the port leaves a bridge. > > Isn't the bridge code programming flooding on the port correctly on > leave/join, > because the BR_*FLOOD flags have been learned? I would expect that.
If you're asking whether the bridge code sends a SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS message on leave/join, it seems that it does not. There is only one place in the bridge code that this message is generated, that is in net/bridge/br_switchdev.c br_switchdev_set_port_flag(). That is called from one place in the bridge code, which is br_set_port_flag() in net/bridge/br_netlink.c, which is in response to a RTM_SETLINK netlink message where the bridge code processes all the various bridge link options. There appears to be no call when adding or removing an interface to/ from a bridge. -- 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
