Interface fallback from preferred to next highest priority

[matte1]

I'm trying to set my configuration up such that it primarily uses eth0; however, many connections are local and if the Ethernet adapter lost power or became unplugged I would like those local connections to continue to work. My expectation here is that I could set the ethernet to be preferred and in the event that interface goes down it would switch to using local i.e.

        <NetworkInterface priority="1" address="192.168.254.1" multicast="true"></NetworkInterface>
        <NetworkInterface priority="0" address="127.0.0.1" multicast="false"></NetworkInterface>

However in practice I see that it always selects local which means I don't see any traffic over the ethernet interface. First of all is what I'm trying to do possible with cyclonedds and then second how can I set my configuration file to get this behavior?

[matte1]

Bump!

[eboasson]

Thanks for Bump!-ing it 🙂

With those priority settings I would expect it to prefer ethernet (especially with multicast disabled over loopback); what I wouldn't expect it to do is to gracefully fall back when the ethernet disappears, simply because it doesn't yet keep track of interfaces coming up and going down. (That needs some rework of internals, there's a PR open that I really want to merge but never seem to get around to: #1080 ... yes, it's old ...)

Anyway, this clearly needs a bit more attention.

[matte1]

Thanks eboasson! This is a key safety feature for us. Do you expect to revive that PR anytime soon or should I look for a workout around to this issue?

[eboasson]

I am pretty sure reviving it means a bit of rework because of the massive cleanup of names and header file organisation that @dpotman did, but I think that beyond that it should basically still apply. I'll have to double-check the progress on "CQ" for including some 3rd party code in the project, bump that if it stalled.

What I am not sure about anymore is why it remained in draft status. The real trouble here is that I don't know when I'll be able to do it. I'd love to fetch it, update it, and merge it if everything checks out. It is a bit of a scary PR because it changes some quite fundamental bits that are really hard to test. But the alternative to updating & merging this PR is to do it all over, because it does rework some weak spots that do need this TLC.

Would you have time and be willing to have a quick look yourself what it means to update it? I find it is much easier to answer questions when there are many things vying for your attention than it is to do substantial real work. Sadly, because I rather like the real work ... Otherwise I'll do my best to make it happen this time round ...