[44net] Re: Strange DNS behavior?

On Sun, May 5, 2024 at 6:00 PM lleachii(a)aol.com <lleachii(a)aol.com> wrote: Interesting. What's curious about this (to me, anyway) is that it's not _just_ packet loss, but (seemingly?) only loss of very specific packets. If the problem were just random UDP packet loss, I'd expect some of the queries that I observe to always succeed to occasionally fail, while some of those that always seem to fail would occasionally succeed. Instead, I see repeatable patterns of success and failure. Indeed, I can alternate queries between succeeding and failure and the results are very consistent. Curiously, in between my original message and now, some queries started working (consistently!) while others still consistently fail. Also, just as a data point, the note about UDP reminded me that I ought to test over TCP, and that works reliably for every case that I tried. I think that's right; I've been running tests from 166.84.136.80. I just tried to send a couple of queries to `dns-mdc.ampr.org` but got no response. If that were the case, I'd expect all success or all failure, or some random combination of success and failure. But instead, I see very specific success and failure cases, with no discernable pattern to what works and what doesn't. It doesn't appear to be totally random, nor is it an all-or-nothing sort of thing. I can think of a few possibilities/questions. 1. Are these packets even making it to the upstream side of AMPRGW? I have no way of knowing, really, and it's possible AMPRGW never sees them. But why just these packets containing these specific PTR queries? I suspect most of them arrive at UCSD upstream, but don't get passed. 2. Does AMPRGW block incoming DNS requests to non-authoritative servers? Or maybe there's an allowlist somewhere I'm not on? This seems unlikely; first, no one seems to know anything about that and I'd figure that they would if that sort of thing existed. Second, if that were the case, I'd suspect all DNS queries to fail, or at least all of a specific type (e.g., all `PTR?` queries or something like that). But that doesn't fit the observed data. 3. Could it be that AMPRGW is doing some kind of deep packet inspection and filtering queries that match certain, specific, filters? I find this hard to believe; from what I know of AMPRGW (which admittedly isn't THAT much, mostly reading between the lines of old posts by Brian Kantor), I just don't think it's that kind of system. What seems more likely to me is that there's something specific, but incidental, about the packets containing these queries that's tickling AMPRGW in just the right way that it's dropping them. I looked at the various stat files on gw.ampr.org/private, but nothing sticks out to me as obvious. Thanks again for the response, Lynwood. - Dan C.