Apr 292015

I have a reasonable size home IPv4/IPv6 network with 10ish devices accessing it most of the time. And all worked in a perfect harmony until one morning when wife told me she cannot print on our wireless printer (cheap Brother MFC-J435W). While printer seemed fine, all computers seemed to think of it as offline. Without resolving problem I went to work only to be greeted with information that wife’s tablet (Asus Prime) isn’t working either.

After some debugging I pronounced network on both devices dead on continued working on a small utility that uses broadcast to share some basic data over network to whoever might be listening. As I upgraded versions from night before with new code, printer suddenly started to print again. For a minute or so and then stopped again. And few more times that evening. Whenever I restarted media server, printer would work for a while.

Well, I believe you get the pattern.

What exactly causes this particular issue is hard to say. My best guess is that something is wrong with IPv4 multicast packet parser (if it even exists) in both devices. Something in my packets is causing device’s network stack to go haywire. I know it isn’t address itself because I tried with a few other multicast addresses with similar issues. I know it isn’t bandwidth issue since total amount of messages was less that 2 KB/s. In any case, I didn’t have too much time to troubleshoot.

End solution was really simple – I stopped sending my packets using IPv4 addresses and relied on IPv6 multicast only. Not only that IPv6 multicast is a first-class citizen but many network stacks ignore it altogether. Regardless of the exact reason, that worked perfectly.

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