From fdc8be4e6d8212f0c3b298587dd9138acbb63df9 Mon Sep 17 00:00:00 2001 From: Ben Pfaff Date: Thu, 3 Sep 2009 12:58:25 -0700 Subject: [PATCH] vswitchd: Explain why mirroring to a VLAN can cause network problems. Bug #1963. --- vswitchd/ovs-vswitchd.conf.5.in | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/vswitchd/ovs-vswitchd.conf.5.in b/vswitchd/ovs-vswitchd.conf.5.in index d613419f..2eb49c13 100644 --- a/vswitchd/ovs-vswitchd.conf.5.in +++ b/vswitchd/ovs-vswitchd.conf.5.in @@ -267,6 +267,22 @@ a trunk port, the frame's VLAN tag will be set to \fIvid\fR, replacing any existing tag; when it is sent out an implicit VLAN port, the frame will not be tagged. This type of mirroring may be referred to as RSPAN. +.IP +Please note that mirroring to a VLAN can disrupt a network that +contains unmanaged switches. Consider an unmanaged physical switch +with two ports: port 1, connected to an end host, and port 2, +connected to an Open vSwitch configured to mirror received packets +into VLAN 123 on port 2. Suppose that the end host sends a packet on +port 1 that the physical switch forwards to port 2. The Open vSwitch +forwards this packet to its destination and then reflects it back on +port 2 in VLAN 123. This reflected packet causes the unmanaged +physical switch to replace the MAC learning table entry, which +correctly pointed to port 1, with one that incorrectly points to port +2. Afterward, the physical switch will direct packets destined for +the end host to the Open vSwitch on port 2, instead of to the end host +on port 1, disrupting connectivity. If mirroring to a VLAN is desired +in this scenario, then the physical switch must be replaced by one +that learns Ethernet addresses on a per-VLAN basis. .ST "Example" The following \fBovs\-vswitchd\fR configuration copies all frames received on \fBeth1\fR or \fBeth2\fR to \fBeth3\fR. -- 2.30.2