When it comes to network safety, many corporations and individuals turn to firewalls and network monitoring applications to control what’s happening. This can keep intrusions at bay, or at least make the life of a potential intruder a bit more difficult. However, these methods can also cause DEVONthink’s synchronization engine to seemingly fail, especially with Bonjour connections.
In System Preferences > Security & Privacy > Firewall, you can turn on your Mac’s firewall. Again, this can keep intruders out, but you need to add an exception for DEVONthink, to allow Sync to work. If your firewall is on, click the Firewall Options button, press the Plus (+) button and add DEVONthink. If you use an application, like Objective Development’s Little Snitch, you will need to put in an exception for DEVONthink as well, or it can keep sync from working properly.
Public WiFi is sometimes set to disallow certain kinds of traffic or non-standard port numbers. Bonjour synchronization uses a non-standard port number to avoid conflicts with services on other ports. They often do this to ensure only routine traffic, like web browsing, emailing, etc., is happening on their network. This also can keep Bonjour synchronization from working.
In this case, if you are only using a Bonjour sync, say between your MacBook and iPad, you can create an ad-hoc network. Click the WiFi icon in your menubar and choose Create Network. Give it a name and a password, and your machine will be automatically connected to it. Now you need to switch the other device to this network and you should be able to sync. Note: You will not be able to access the Internet when connected this way, so use it when you need to. When you’re done, click the WiFi icon again and choose Disconnect from…
On a larger scale corporations often use firewalls and other sophisticated methods to monitor and control the traffic on their networks. If need be, you may be able to use an ad-hoc network, but be sure you are not running afoul of any company security policies. Otherwise, you may be able to talk to your IT department about allowing the port assigned in DEVONthink’s Preferences > Sync > Bonjour Options.