Currently, "significantly more loaded" means that H must carry at
least 1 Mbps more traffic, and that traffic must be at least 3%
greater than L's.
+
+Bond Balance Modes
+------------------
+
+Each bond balancing mode has different considerations, described
+below.
+
+LACP Bonding
+------------
+
+LACP bonding requires the remote switch to implement LACP, but it is
+otherwise very simple in that, after LACP negotiation is complete,
+there is no need for special handling of received packets.
+
+SLB Bonding
+-----------
+
+SLB bonding allows a limited form of load balancing without the remote
+switch's knowledge or cooperation. The basics of SLB are simple. SLB
+assigns each source MAC+VLAN pair to a link and transmits all packets
+from that MAC+VLAN through that link. Learning in the remote switch
+causes it to send packets to that MAC+VLAN through the same link.
+
+SLB bonding has the following complications:
+
+ 0. When the remote switch has not learned the MAC for the
+ destination of a unicast packet and hence floods the packet to
+ all of the links on the SLB bond, Open vSwitch will forward
+ duplicate packets, one per link, to each other switch port.
+
+ Open vSwitch does not solve this problem.
+
+ 1. When the remote switch receives a multicast or broadcast packet
+ from a port not on the SLB bond, it will forward it to all of
+ the links in the SLB bond. This would cause packet duplication
+ if not handled specially.
+
+ Open vSwitch avoids packet duplication by accepting multicast
+ and broadcast packets on only the active slave, and dropping
+ multicast and broadcast packets on all other slaves.
+
+ 2. When Open vSwitch forwards a multicast or broadcast packet to a
+ link in the SLB bond other than the active slave, the remote
+ switch will forward it to all of the other links in the SLB
+ bond, including the active slave. Without special handling,
+ this would mean that Open vSwitch would forward a second copy of
+ the packet to each switch port (other than the bond), including
+ the port that originated the packet.
+
+ Open vSwitch deals with this case by dropping packets received
+ on any SLB bonded link that have a source MAC+VLAN that has been
+ learned on any other port. (This means that SLB as implemented
+ in Open vSwitch relies critically on MAC learning. Notably, SLB
+ is incompatible with the "flood_vlans" feature.)
+
+ 3. Suppose that a MAC+VLAN moves to an SLB bond from another port
+ (e.g. when a VM is migrated from this hypervisor to a different
+ one). Without additional special handling, Open vSwitch will
+ not notice until the MAC learning entry expires, up to 60
+ seconds later as a consequence of rule #2.
+
+ Open vSwitch avoids a 60-second delay by listening for
+ gratuitous ARPs, which VMs commonly emit upon migration. As an
+ exception to rule #2, a gratuitous ARP received on an SLB bond
+ is not dropped and updates the MAC learning table in the usual
+ way. (If a move does not trigger a gratuitous ARP, or if the
+ gratuitous ARP is lost in the network, then a 60-second delay
+ still occurs.)
+
+ 4. Suppose that a MAC+VLAN moves from an SLB bond to another port
+ (e.g. when a VM is migrated from a different hypervisor to this
+ one), that the MAC+VLAN emits a gratuitous ARP, and that Open
+ vSwitch forwards that gratuitous ARP to a link in the SLB bond
+ other than the active slave. The remote switch will forward the
+ gratuitous ARP to all of the other links in the SLB bond,
+ including the active slave. Without additional special
+ handling, this would mean that Open vSwitch would learn that the
+ MAC+VLAN was located on the SLB bond, as a consequence of rule
+ #3.
+
+ Open vSwitch avoids this problem by "locking" the MAC learning
+ table entry for a MAC+VLAN from which a gratuitous ARP was
+ received from a non-SLB bond port. For 5 seconds, a locked MAC
+ learning table entry will not be updated based on a gratuitous
+ ARP received on a SLB bond.
projects / openvswitch / commitdiff