Hallo, * Antoine Beaupre [Thu, Oct 10 2019, 12:36:21PM]: > Package: apt-cacher-ng > Version: 3.2-2 > Severity: normal > Tags: ipv6 > > apt-cacher-ng does not deal well with dual-stack failures. At home I > regularly have trouble with my IPv6 connexions, which just hang. Most > applications are able to recover from this and fallback to IPv4, which > just works. This is therefore mostly transparent to users, at worst > there's a slight delay during the switchover.
Okay, I agree. I also experience such situations, rarely, when the crap modem from my provider gets upset and fails to route IPv6 (but still reports full IPv6 connectivity in its diagnostics). > The way to deal with this is documented in RFC 8305 and is generally > refered to as "happy eyeballs": > > https://en.wikipedia.org/wiki/Happy_Eyeballs Not sure this is feasible exactly the way they describe there. This RFC is apparently mostly by DNS timing behavior but ACNG currently uses getaddrinfo which delivers all collected DNS data at once. What I intend to implement instead is a similar scheme: a) get all DNS records like ATM b) filter to IPv4 or IPv6 or both (depending on user preference in <ConnectProto> setting) c) auto-sort the list so that the first entry is v4 or v6 (depending on <ConnectProto> preference) and the following ones are alternativing d) start connecting on the first entry e) when nothing happened after N seconds, start a second connection attempt in parallel (using the second address, which is of different family then) f) if the second background connect attmpt fails after N, abort it, try the next DNS entry in the sequence, etc. etc. (while the first connect attempt is still ongoing, until <NetworkTimeout> seconds is reached) Questions: a) do you consider this reasonable enough? b) would you like to become a tester for this, in case you can reproduce this regularly? (I can fake the test case but nothing beats the real thing) c) any good name proposal for N? I think about "FastTimeout" (vs. NetworkTimeout) d) good default value for N? I'd consider 5s (while NetworkTimeout: 60s currently) Best regards, Eduard.
