:memo: Explain how to troubleshoot container DNS issue

Guides/proxmox.md

@@ -86,3 +86,9 @@ DNS : 192.168.122.1 -> 192.168.1.1 (l'adresse de la box)
 Et mettre DHCP sur l'adresse IP ... et ça marche !
 
 (Une IP fixe devrait marcher)
+
+#### Trouble shoot container having DNS but does not reach Internet
+
+Set the right gateway to the next thing.
+
+For the ISF practice session, it was on the linux bridge.