There is a nice list of the used ports listed in this Knowledge Base article:
https://support.docuware.com/en-us/knowledgebase/article/KBA-34951
However, Intelligent Indexing works over http/https, so use Your preferred tools to check layers 2/3 for connections to the url of the Intelligent Indexing Service, which you can find in the intelligent indexing module of the web configuration.
It might well be a DNS issue, so You may want to verify the the URL can be properly resolved.