Part 4: Test everything including breaking it!

At this point if everything works you should be able to ping between the networks.  If that isn’t working then you need to troubleshoot what is breaking down communication wise.  This could be anything from the two local routers not sharing routes to the routers not talking over zerotier.  The point I am trying to push across is that there is no simple gotchas I can offer troubleshooting steps for.

Once connectivity across the LANs is working, the next good thing you want to do is break it of course.  First simple break I would suggest is just reboot the router vms.  Ideally if everything is setup right and once they are booted back up and the services start, routing should be restored and everything should work again.  Again if things do not work the next thing to do is troubleshoot and solve, as there are to many possibilities to mention.  I would even suggest break the routing demons and make sure you can repair them as needed.

At the end of this now you have a working multi-site lan that each site has its own working IP subnet.

Final comment: People have asked me is it possible to bridge LANs?  The answer is yes but that is an entirely different process and one I would not recommend.

2 thoughts on “Part 4: Test everything including breaking it!

    1. mindlesstux Post author

      Shotgun answer as I do not want to try to format and make sure the thought is complete/in order.

      Short answer, network broadcast domains.

      Either in total time between Device A to Device Z (say 300ms for US East Coast to Sydney) or the number of devices trying to broadcast at once. I mention time due to thinking about things that are round trip time dependant. IF you try to use something in the same subnet it is usually thought of as it is local. NFS is a horrible example but might work here. NFS needs a full round trip, if the whole thing is bridged together I can see mistakes made. Example one massive network and a couple of NFS servers at 192.168.100.5 and a clone of 192.168.100.25. Can you tell me with 100% certainty looking at just the IP without doing anything else which would be US east and which is in Sydney? Most people will go no. If the addresses are 192.168.100.5 and 192.168.200.5, I can say .5 is NFS server, .100 is location, 192.168 is the prefix. Local traffic stays local and remote traffic gets routed out. The timing of round trip would trip up NFS, as it goes client->server->client, so if it is 250ms to go US East to Sydney NFS spends 500ms on time for there and back of a request.

      If you ignore time, then there is the number of devices in one network segment. Everything likes to be chatty on L2 broadcast. Let’s say you have 1000+ devices in one L2 domain across two sites on either side of the world. You will have a flood of stuff screaming out who has X IP or the like of. Let’s say you have a 100mbit connection on both ends, you would now be chewing up 5mbit (excessive but to show the point) of nothing but network broadcast traffic that does not need to go the other side of the world. If you break up the segments, only broadcast traffic that is relevant to say us east would stay just in us east and your connection would not be shoving 5mbit/s of broadcast traffic.

      Basically, boils down to why would I spend cpu cycles trying to shove packets that are only relevant to one area into another?

      Reply

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