In a setup where debugging works flawlessly when connected to the internet, the debugger takes so long to respond that it becomes unusable when no internet connection is present. My setup is the latest versions of both debugger and editor, but the problem has been present at least since version 6.2 (my previous post about this: http://forum.nusphere.com/very-slow-debugger-response-from-vmware-ws-freebsd-server-t8332.html?highlight=slow). We are running both Win 7 and 8 (64 bit) and FreeBSD 8.x and 9.x - 32 and 64 bit versions, the problem is the same for all setups.

I've done a little digging, and found the following:

* When not connected to the internet, the debugger takes exactly 30 seconds to respond every time (indictating something has to time out first).
* I've logged dns lookups and do not see the debugger looking up anything using the default dns server, indicating a (reverse) lookup timeout is not the problem.
* When the connection is finally made, all works well until the session finishes (e.g. singlestepping, breakpoints). The next time a debug session is started, the problem is back.
* Reconnecting the the internet makes the problem go away instantly.

It would seem like the debugger is trying to connect to an outside server whenever a debug session is started (is an external dns server used?). A packet sniffer would of course help determine if this is the case, but I don't feel like spending time on doing that.

This problem makes our setup unusable in any setting where we are not connected to the internet, which is a major problem for us.

Help very much appreciated!

You must be doing something wrong.
Debugger does not depend on internet at all.
What it needs is
1) connectivity to your development machine. In case if you run debug remotetely, the connectivity means that you can access to your server and server can access to your development machine. Internet is not involved for this. Everything can run in your home or corporate network.
2) connectivity to your name server (DNS) if you use names in debug.host_allow/debug.host_deny settings

Neither case affect pages running without request for debugger, unless you enabled JIT debug and have errors/warnings/notices in your php code or left some DebugBreak() calls in your code. In such cases debugger tries to connect back to PhpED which is expected to be running on your development machine. If you don't have this machine running or your network is broken somehow, this may take 30 seconds to timeout. It's an expected behaviour. If it's not what you need, just do not set JIT enabled on production servers and do never leave JIT enabled if you don't keep PhpED running and make sure you don't have DebugBreak() calls.