Signed-off-by: Ben Pfaff <[email protected]>
---
FAQ | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/FAQ b/FAQ
index 75d9007..5406e84 100644
--- a/FAQ
+++ b/FAQ
@@ -250,6 +250,40 @@ A: The following commands configure br0 with eth0 and tap0
as trunk
ovs-vsctl clear bridge br0 mirrors
+Q: Does Open vSwitch support configuring a port in promiscuous mode?
+
+A: Yes. How you configure it depends on what you mean by "promiscuous
+ mode":
+
+ - Conventionally, "promiscuous mode" is a feature of a network
+ interface card. Ordinarily, a NIC passes to the CPU only the
+ packets actually destined to its host machine. It discards
+ the rest to avoid wasting memory and CPU cycles. When
+ promiscuous mode is enable, however, it passes every packet to
+ the CPU. On an old-style shared-media or hub-based network,
+ this allows the host to spy on all packets on the network.
+ But in the switched networks you'll find pretty much
+ everywhere these days, promiscuous mode doesn't have much
+ effect, because few packets not destined to a host are
+ delivered to the host's NIC.
+
+ This form of promiscuous mode is configured in the guest OS of
+ the VMs on your bridge, e.g. with "ifconfig".
+
+ - The VMware vSwitch uses a different definition of "promiscuous
+ mode". When you configure promiscuous mode on a VMware vNIC,
+ the vSwitch sends a copy of every packet received by the
+ vSwitch to that vNIC. That has a much bigger effect than just
+ enabling promiscuous mode in a guest OS. Rather than getting
+ a few stray packets for which the switch does not yet know the
+ correct destination, the vNIC gets every packet. The effect
+ is similar to replacing the vSwitch by a virtual hub.
+
+ This "promiscuous mode" is what switches normally call "port
+ mirroring" or "SPAN". For information on how to configure
+ SPAN, see "How do I configure a port as a SPAN port, that is,
+ enable mirroring of all traffic to that port?"
+
Q: How do I configure a VLAN as an RSPAN VLAN, that is, enable
mirroring of all traffic to that VLAN?
--
1.7.10.4
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