doc: add a word about Intel X710 with embedded LLDP daemon

diff --git a/README.md b/README.md
index a73ae5e9ccc5bb23ef328e987c6548651bd8a95d..9d599c3d86efe01ffbb5eb56188a7bb87e0003ff 100644 (file)
--- a/README.md
+++ b/README.md
@@ -298,6 +298,14 @@ You can use `tcpdump` to look after the packets received and send by
 
     tcpdump -s0 -vv -pni eth0 ether dst 01:80:c2:00:00:0e
 
+Intel X710 cards may handle LLDP themselves, intercepting any incoming
+packets. If you don't see anything through `tcpdump`, check if you
+have such a card (with `lspci`) and stop the embedded LLDP daemon:
+
+    for f in /sys/kernel/debug/i40e/*/command; do
+        echo lldp stop > $f
+    done
+
 License
 -------