What's the configuration? This has to do with connecting your computer to the Pi, right? When you say you connect to the router, do you mean via ethernet? Then, what's the IP of your computer? Does this error message show up in the Pi or your computer? What the IP of the Pi? Better post your patch...

@toddak I am pretty sure it is a long standing bug in the osx network stack. There have been a lot of complaints over the years. The only solution found is to shut down the socket (wlan0 probably) flush the cache and then restart the socket.... (for your mac!).... or just to reboot it..... which some people have found to be absolutely the only solution....
I hope that works for you as well!
David.

@whale-av Its just feels odd to me that it works fine on the Home network, but doesn't work on the other router. I would have thought that if it was an issue with OSX, then it wouldn't work on either. Is that a fair assumption?

I did manage to get PD to generate another two error messages:

netsend: Connection refused (61)

warning: 11 removed from poll list but not found
connecting to port 9001
netsend: Network is unreachable (51)

warning: 11 removed from poll list but not found

Could there be something in the router that needs changing? Alternatively, could it have anything to do with the edits I made to the /etc/network/interfaces file?

@alexandros -So the pi and my computer are connected to the router via wifi, not via an ethernet cable. Its the same idea that was working before when I used my home router, only know I'm using a different router. That's the only difference in the system.

As far as I know the IP address of my laptop is not static, so I've been using that to send from just for tests. I've set up the pi with the static IP address of 10.1.1.101, and that has been working fine on the home network.

The error message appears on my computer, the sender. I'm just using the receiver/sender_udp patches you gave me, but have updated the IP address to 10.1.1.101.

@toddak Have you tried re-booting the mac? (after making the Linksys your preferred network).
Normally netsend in udp mode should not care even if you have turned off all your network adapters. I am (almost) certain that the error messages are being returned by the os.
I wonder if osx will not connect properly to the Linksys because there is no internet connection? I hope not!, but osx, is at least as intrusive as the new windows 10.
You should definitely fix your Ip address for the mac for the Linksys network location. It could be very important later in your project that addresses never change.
What version of the wrt54 did you get (printed on the label on the bottom somewhere). If I have one the same I could send you a configuration file........
David.

If you're connected to another router it's very likely that your computer gets a different IP, if it's using DHCP instead of a static IP. In this case, you should probably log in the Pi via SSH (you can use ssh -X pi@raspberrypi.local if you're not sure about its IP) and once you know your computer's IP, change the Pi's patch accordingly.
I believe it's better to have a connection over ethernet and set a static IP both for the Pi and your laptop for their ethernet connection and leave their wi-fi untouched so you can log it any router and the internet without problems.

@alexandros Hello Alexandros..... He needs wifi for his project, and the Pi's are already static....
David.

@whale-av then I guess he'll need some scripting...
@toddak I think that you can send data via OSC to the IP address 255.255.255.0 and given that the port is the same for the sender and the receiver, the message will arrive to any recipient in the network. So you can maybe use that to send the Pi's IP to your laptop on boot (using the script I've posted in an earlier reply) and then start sending from your computer to the Pi. You can probably use the same technique to send your computer's IP to the Pi as well...

@alexandros Hello Alexandros..... He will always know the PI's IPs (it's almost poetry isn't it!) because they will be (are already I hope) fixed. He is going to send different messages to each one...... so no multicast....
I think I should start a chat with him for the network setup. The patch problem is solved, and this thread has become very long.............. !!
His whole setup works fine on his home network, but it looks as though his mac (the central control) is not communicating properly with the router that will be used for the show.........
David.

@whale-av I guess I've been partly understanding this thread cause I've been partly reading the posts, to be honest... sorry for throwing random stuff in this conversation.

@alexandros That's ok....... it could have been useful (and in fact it could help someone else that stumbles across it later!).........
It's a problem with threads as long and twisted as this one......
David.

Yes, it is quite a long and twisted thread, but I feel like it needed to be. Trying to trouble shoot this problem across two forums would have been huge, and its been a massive help finding people who are fluent in both areas I'm dealing with, so thanks again!

@whale-av I still don't understand why mac os would be ok with one router, and not another. That feels weird to me.

I got the WRT54GL v1.1. I've tried re-booting the mac with linksys as my preferred network, but its doesn't make a difference. I still get 'Network is unreachable (51) coming up.

I'll send you my email, very happy for the network help if its on offer! Its just not behaving, or rather misbehaving, in a way that makes sense to me right now.

@toddak Hello Toddak.......
I will post this here first. Error 51 is (for a mac).........
"51 ENETUNREACH Network is unreachable. A socket operation was attempted to an unreachable network."
So I will try to get the same error in my OSX partition, but it might take a while!.
Googling that error brings up a lot of chat about VPN's...........? are you running one on your home-to-work network?
Are you using "udp" for "netsend" (the -u -b switches I think)?
Do you get the message if you open just Pd........ before you open a patch?
Are you sure you are connected? Check by "pinging" a Pi? Check by pinging the router?
If you link (with a network cable) the "wan" (single rj45 socket) of the Linksys to your home network does that fix the problem.
Has the mac the correct information in the "prefs" netwok page..... Ip, subnet. Gateway that match the router info?
I will email you now so that you can send me as much as you have already found out........, and when I get a chance I will email you a zip of some screenshots of "good" router setup pages for your project....
David.

@whale-av Finally, something about networking just clicked and I think I solved my issue. Posting here as it resolves some of the thread and might help others.

When setting up the second pi, it was connected to the network that will be used in the field, not the home network. When I was looking at all the addresses for Broadcast, network, etc, they all looked substantially different, and I remembered an earlier comment in this thread about issues using different subnets.

Bam. Lightbulb moment. It wasn't working because all the broadcast, network, etc setting were found when connected to the home network, not the 'field' network. When I set it up using the setting on the field router, and connected my laptop to this network too, all was fine.

There still might be an issue in getting it to connect automatically to a network, but we'll save that for email when, and if, it happens.

@toddak

Wow, just read through this whole thread, 4 yrs later. I relate to all the obstacles as I'm too building something that requires networking. When you think you've finally got it right, something else comes up hehe. I'm curious though, how did your project turn out?? Are there any photos/videos/recordings of your show?
Best regards // Anton