doc: announce ixgbe MTU setting limitation

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>

diff --git a/doc/guides/nics/ixgbe.rst b/doc/guides/nics/ixgbe.rst
index 05ecc2a..aceeb13 100644 (file)
--- a/doc/guides/nics/ixgbe.rst
+++ b/doc/guides/nics/ixgbe.rst
@@ -233,6 +233,15 @@ be calculated as follows:
 
 In order to ensure valid results, it is recommended to poll every 4 minutes.
 
+MTU setting
+~~~~~~~~~~~
+
+Although the user can set the MTU separately on PF and VF ports, the ixgbe NIC
+only supports one global MTU per physical port.
+So when the user sets different MTUs on PF and VF ports in one physical port,
+the real MTU for all these PF and VF ports is the largest value set.
+This behavior is based on the kernel driver behavior.
+
 
 Supported Chipsets and NICs
 ---------------------------