Add section on outgoing IP/firewall to Troubleshooting

mkdocs/docs/HPC/troubleshooting.md

@@ -291,6 +291,23 @@ ssh -vvv {{ userid }}@{{ loginnode }}
 and include the output of that command in the message.
 {% endif %}
 
+{% if site == gent %}
+## Issues reaching servers from HPC infrastructure
+
+If you have to reach license servers from {{ hpcinfra }} systems or you 
+have to directly load some database here, then it might not work (you will get 
+network connection timed out or network connection refused error). Our
+firewall rules are quite strict, we only allow outging ports 22 (SSH protocol),
+ 80 (HTTP protocol), and 443 (HTTPS protcol), so if your download or license server 
+requires other ports, then we should make a modification in our firewall settings.
+For this, please contact us via <{{ hpcinfo }}>, and send the destination IP and ports. 
+(We only open our fireall for static IP addresses).
+
+It might possible, that the other end has also firewall, or the license server restricts 
+the incoming IP addresses. In this case you need the outgoing IP address of our systems,
+which is either `157.193.240.251` (nathpca001.ugent.be) or `157.193.241.251` (nathpcb001.ugent.be).
+{% endif %}
+
 ## Security warning about invalid host key
 
 If you get a warning that looks like the one below, it is possible that