After a bit of digging, we discovered that a service called Bonjour was installed and running. I stopped the service, set it to disabled, and restarted the PC. This fixed the issue. It didn’t seem to affect how Extensis Portfolio operates, so I’m not sure why they are installing the service. A quick google search shows quite a few people with Bonjour network issues, so apparently it is a service used by quite a few software vendors.