+Q: I created a GRE port using ovs-vsctl so why can't I send traffic or
+ see the port in the datapath?
+
+A: On Linux kernels before 3.11, the OVS GRE module and Linux GRE module
+ cannot be loaded at the same time. It is likely that on your system the
+ Linux GRE module is already loaded and blocking OVS (to confirm, check
+ dmesg for errors regarding GRE registration). To fix this, unload all
+ GRE modules that appear in lsmod as well as the OVS kernel module. You
+ can then reload the OVS module following the directions in INSTALL,
+ which will ensure that dependencies are satisfied.
+
+Q: Open vSwitch does not seem to obey my packet filter rules.
+
+A: It depends on mechanisms and configurations you want to use.
+
+ You cannot usefully use typical packet filters, like iptables, on
+ physical Ethernet ports that you add to an Open vSwitch bridge.
+ This is because Open vSwitch captures packets from the interface at
+ a layer lower below where typical packet-filter implementations
+ install their hooks. (This actually applies to any interface of
+ type "system" that you might add to an Open vSwitch bridge.)
+
+ You can usefully use typical packet filters on Open vSwitch
+ internal ports as they are mostly ordinary interfaces from the point
+ of view of packet filters.
+
+ For example, suppose you create a bridge br0 and add Ethernet port
+ eth0 to it. Then you can usefully add iptables rules to affect the
+ internal interface br0, but not the physical interface eth0. (br0
+ is also where you would add an IP address, as discussed elsewhere
+ in the FAQ.)
+
+ For simple filtering rules, it might be possible to achieve similar
+ results by installing appropriate OpenFlow flows instead.
+
+ If the use of a particular packet filter setup is essential, Open
+ vSwitch might not be the best choice for you. On Linux, you might
+ want to consider using the Linux Bridge. (This is the only choice if
+ you want to use ebtables rules.) On NetBSD, you might want to
+ consider using the bridge(4) with BRIDGE_IPF option.
+