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

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

diff --git a/virt-top/virt-top.pod b/virt-top/virt-top.pod
index e11e814..4d7df4e 100755 (executable)
--- a/virt-top/virt-top.pod
+++ b/virt-top/virt-top.pod
@@ -369,6 +369,21 @@ Note that in the current implementation, options specified in
 the init file override options specified on the command line.
 This is a bug and this behaviour may change in the future.
 
 the init file override options specified on the command line.
 This is a bug and this behaviour may change in the future.
 

+=head1 NOTES
+
+=head2 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.
+

 =head1 SEE ALSO
 
 L<top(1)>,
 =head1 SEE ALSO
 
 L<top(1)>,