Document background noise of RX packets from bridges (RHBZ#647987).

[virt-top.git] / virt-top / virt-top.txt

diff --git a/virt-top/virt-top.txt b/virt-top/virt-top.txt
index da737b8..de0681e 100644 (file)
--- a/virt-top/virt-top.txt
+++ b/virt-top/virt-top.txt
@@ -269,6 +269,19 @@ INIT FILE
     file override options specified on the command line. This is a bug and
     this behaviour may change in the future.
 
+NOTES
+  NETWORK RX BYTES AND PACKETS
+    Libvirt/virt-top has no way to know that a packet transmitted to a guest
+    was received (eg. if the guest is not listening). In the network RX
+    stats, virt-top reports the packets transmitted to the guest, on the
+    basis that the guest might receive them.
+
+    In particular this includes broadcast packets. Because of the way that
+    Linux bridges work, if the guest is connected to a bridge, it will
+    probably see a steady "background noise" of RX packets even when the
+    network interface is idle or down. These are caused by STP packets
+    generated by the bridge.
+
 SEE ALSO
     top(1), virsh(1), <http://www.libvirt.org/ocaml/>,
     <http://www.libvirt.org/>, <http://people.redhat.com/~rjones/>,