@@ -944,7 +944,22 @@ A: The short answer is that this is a misuse of a "tap" device. Use
Quality of Service (QoS)
------------------------
-### Q: How do I configure Quality of Service (QoS)?
+### Q: Does OVS support Quality of Service (QoS)?
+
+A: Yes. However, it only support traffic shaping on egress traffic;
+ ingress traffic is limited to policing. Policing is a simple form of
+ quality-of-service that simply drops packets received in excess of
+ the configured rate. Due to its simplicity, policing is usually less
+ accurate and less effective than egress traffic shaping, which queues
+ packets.
+
+ Keep in mind that ingress and egress are from the perspective of the
+ switch. That means that egress shaping limits the rate at which
+ traffic is allowed to transmit from a physical interface, but the
+ rate at which traffic will be received on a virtual machine's VIF.
+ For ingress policing, the behavior is the opposite.
+
+### Q: How do I configure egress traffic shaping?
A: Suppose that you want to set up bridge br0 connected to physical
Ethernet port eth0 (a 1 Gbps device) and virtual machine interfaces
@@ -1006,6 +1021,20 @@ A: Suppose that you want to set up bridge br0 connected to physical
--all option), then you will have to destroy QoS and Queue records
individually.
+### Q: How do I configure ingress policing?
+
+A: A policing policy can be configured on an interface to drop packets
+ that arrive at a higher rate than the configured value. For example,
+ the following commands will rate-limit traffic that vif1.0 may
+ generate to 10Mbps:
+
+ ovs-vsctl set interface vif1.0 ingress_policing_rate=10000
+ ovs-vsctl set interface vif1.0 ingress_policing_burst=1000
+
+ Traffic policing can interact poorly with some network protocols and
+ can have surprising results. The "Ingress Policing" section of
+ ovs-vswitchd.conf.db(5) discusses the issues in greater detail.
+
### Q: I configured Quality of Service (QoS) in my OpenFlow network by
adding records to the QoS and Queue table, but the results aren't
what I expect.
Signed-off-by: Justin Pettit <jpettit@nicira.com> --- FAQ.md | 31 ++++++++++++++++++++++++++++++- 1 files changed, 30 insertions(+), 1 deletions(-)