Symantec Protection for SharePoint servers are showing offline or unable to register new Protection Engine Servers.
The Service is running on the servers showing as offline or you are attempting to register the Protection Engine server. Ports 9455, 9466 are open between the Symantec Protection for SharePoint Servers and port 1344 is open between the Symantec Protection for SharePoint servers and the Protection Engine servers.
NSLOOKUP either show the incorrect IP on resolving the hostname and/or the IP address either does not resolve or resolve to a different host.
The SharePoint servers with Symantec Protection For SharePoint servers is installed may show as offline in the Farm overview.
When registering a new Protection Engine scanner to a Farm server the connection can appear to hang or will time out.
Symantec Protection for SharePoint server requires both forward (hostname to IP) and Reverse (IP to hostname) to function correctly.
Update DNS server so both forward and reverse lookups correct identify the SharePoint server.