Hi taps, At the mike, I believe Gorry asked whether I need sender TTL, and I replied "Yes."
I want to add a little nuance to that: I think a default value for TTL that reaches remote receivers is probably the right choice, so that it's an optional setting (as opposed to today's default of 1 for multicast packets, which you have to always set if you want non-LAN traffic). I think asking application developers to choose an integer value is almost certainly harmful, to the extent it has any effect. At least, I'm certain that when I've set the value out of necessity, I have done so in an entirely unprincipled way, with a goal best phrased as "works for me". (Though I think some people might have real reasons they'd pick specific values, so maybe it has to be allowed.) Some sending use cases are for LAN only (e.g. many discovery and hello protocols), and I think that's why the default for multicast when sending from sockets is TTL=1, and you have to change it--if you forget to set it, you won't blow anything out, you'll just say "huh, I guess multicast doesn't work". I think that probably made sense back when people still thought dense-mode and global source-active announcements might be a good idea, but now maybe it doesn't have to be that way. (Or if anybody thinks that's unsafe, maybe only for ASM?) Anyway, I think in my perfect world, sender TTL for multicast UDP would default to a system-overrideable high value named "global" something, with a corresponding system-overrideable low value named "local" something defaulted to 1, and maybe (if anyone cares) a middle thing named "site" something, and maybe even all the rest of the scopes if you can find me someone who uses them that I can talk to. (And for IP6 these could be inferred and defaulted from the group address's scope[1], with optional override.) Something like that would be way better IMO (as an app dev and/or network admin) than our default TTL=1 world in BSD sockets. But all we really need is a local/not-local selection, and somebody probably does really need to be able to pick a specific value sometimes, because people are just that crazy. (And I would be totally comfortable with making that a privileged operation, btw, if we've got such a concept...) I'll fold this into my #150 resolution proposal[2] when I get there, but I wanted to kick off discussion on this point if anybody has opinions. So please comment if this email makes any sense to you, or ask questions if it doesn't. Best, Jake [1] https://tools.ietf.org/html/rfc7346#section-2 [2] https://github.com/ietf-tapswg/api-drafts/issues/150 _______________________________________________ Taps mailing list [email protected] https://www.ietf.org/mailman/listinfo/taps
