Very odd networking failure...

[thmoore]

I'm having trouble sorting this out. I'm getting TCP/IP via Ethernet working not at all and AirPort working only intermittently on my iMac DV. From reboot to reboot, I get differing results. Sometimes AirPort works and sometimes it doesn't, but Ethernet seems to be switched off somehow. Fiddling with different setups in the "Network" preference panel have no effect.

In OS X, if I open up the "Connect to Server..." window, I can see other Macs on the network via AppleTalk, but get nothing via "Local Network." IE and Eudora fail to make connections.

What's odd is that with the same TCP/IP settings in OS 9 (static IP address talking to a DSL router), settings that I've been using on this machine for years, everything works fine, via AirPort or Ethernet. In OS X, I actually have to unplug the Ethernet cable to get AirPort to work.

I'm thinking that it may have something to do with the fact that I recently gave up on using gNAT as a Software Base Station replacement, and bought a hardware base station. I told gNAT not to share anymore, and not to start up at system startup, but I'm suspecting that if changed a pref somewhere.

I even ditched the "System" folder and reinstalled OS X -- no dice. (Though I'm guessing there may have been offending prefs somewhere in my user directory...)

Lastly, plugging another Mac into the same Ethernet cable in OS X works just fine.

This is a little frustrating, because it's the kind of thing I was really good at troubleshootiong in Classic Mac OSes. Now, I feel like I'm at sea.

Any thoughts? Thank you!

Tom Moore

[Novajo]

Check to make sure that natd isn't running, just in case.

Take the Process Viewer, look at All Processes and look for natd. If it is running, then you have "a problem" and should kill it. If natd isn't running but that your firewall is set up to divert the packets to natd, your network connection will fail.

In the terminal type:

sudo ipfw show

If you get something like:

...
02100 21493 11775173 divert 8668 ip from any to any via ppp0
...
(the divert is the key word), then this means that you must flush the firewall rules that is diverting packets to natd. You do that in the terminal by typing:

sudo ipfw flush

[thmoore]

Well, I'll be dipped. That was indeed it. I first received this:

[localhost:~] tom% sudo ipfw show

00100 108 7185 divert 8668 ip from any to any via en0
00200 93041 38799078 allow ip from any to any
65535 290 29104 allow ip from any to any

...replied with this:

[localhost:~] tom% sudo ipfw flush
Are you sure? [yn] y

Flushed all rules.

...and now get this:

[localhost:~] tom% sudo ipfw show
65535 290 29104 allow ip from any to any
[localhost:~] tom%

...and it works great.

Novajo, many thanks for your unbelievably quick and quite complete response. I'm in your debt.

Tom Moore

[Novajo]

You will now have to find exactly where the firewall is started. I am guessing there must be an item in /Library/StartupItems/ that does it. Sometimes, it is in a natd.conf file. Look for anything that is natd or ipfw related. In /Library/StartupItems/, you can also give this a try:

grep -r divert *

and look at the files that it gives you with the word "divert".

[thmoore]

There was indeed. gNAT still had a file in there. Thanks again!

Tom