diff --git a/isp_box_config.md b/isp_box_config.md
index b34c9ff8..4ba64c2d 100644
--- a/isp_box_config.md
+++ b/isp_box_config.md
@@ -15,10 +15,15 @@ TCP : 22, 25, 53, 80, 443, 465, 993, 5222, 5269, 5290
 #####UPnP
 
 L’UPnP permit opening automatically ports.
+
+In some case, after changing your box configuration (ex: add IPv6, or unlock SMTP ... ) and a reboot. It happens that ports are no onger opened. So you have to reload your firewall configuration :
+
+```sudo yunohost firewall reload```
+
 #####Manual opening ports
 
 In the case that UPnP doesn’t works, manual opening ports are necessary.
 
 #####Email
 
-Internet service porviders blocks port 25 to avoid spam. To send mails, you’ll need to open port 25.
\ No newline at end of file
+Internet service porviders blocks port 25 to avoid spam. To send mails, you’ll need to open port 25.