vlan-test: Add examples of vlan problems to man page.

1 files changed, 19 insertions, 0 deletions

diff --git a/utilities/ovs-vlan-test.8.in b/utilities/ovs-vlan-test.8.in
index d3cd03165..82b4cf7d8 100644
--- a/utilities/ovs-vlan-test.8.in
+++ b/utilities/ovs-vlan-test.8.in
@@ -16,6 +16,25 @@ test, configure Open vSwitch to tag traffic originating from \fIvlan_ip\fR and
 forward it out the target interface. Then run the \fBovs\-vlan\-test\fR in
 client mode connecting to an \fBovs\-vlan\-test\fR server.
 \fBovs\-vlan\-test\fR will display "OK" if it did not detect problems.
+.PP
+Some examples of the types of problems that may be encountered are:
+.IP \(bu
+When NICs use vlan stripping on receive they must pass a pointer to
+a vlan group when reporting the stripped tag to the networking core.
+If there is no vlan group in use then some drivers just drop the
+extracted tag.  Drivers are supposed to only enable stripping if a
+vlan group is registered but not all of them do that.
+.
+.IP \(bu
+Some drivers size their receive buffers based on whether a vlan
+group is enabled, meaning that a maximum size packet with a vlan tag
+will not fit if a vlan group is not configured.
+.
+.IP \(bu
+On transmit some drivers expect that vlan acceleration will be used
+if it is available (which can only be done if a vlan group is
+configured).  In these cases, the driver may fail to parse the packet
+and correctly setup checksum offloading and/or TSO.
 .
 .SS "Client Mode"
 An \fBovs\-vlan\-test\fR client may be run on a host to check for VLAN