Earlier quoted context omitted.
Apparently MacOS doesn't check the checksums.
What about all of the routers involved in the connection?
An IP router can function perfectly well without knowing anything at all about TCP, UDP, or any other protocol.
AT&T Fiber in the SF Bay Area is flipping bits
101–110 of 374 posts
Re: AT&T Fiber in the SF Bay Area is flipping bits
#102Why doesnt TCP reject the flip bits when the checksum fails?
The TCP checksum catches some issues but it won't detect everything. Other newer algorithms like CRC32C[0] are much more effective at detecting corrupt data.
The following is an excerpt from Performance of Checksums and CRCs over Real Data[1].
The TCP checksum is a 16-bit ones-complement sum of the data. This sum will catch any burst error of 15bits or less[8], and all 16-bit burst errors except for those which replace one 1’s complement zero with another (i.e., 16 adjacent 1 bits replaced by 16 zero bits, or vice-versa). Over uniformly distributed data, it is expected to detect other types of errors at a rate proportional to 1 in 2^16.
If you're deeply interested in this topic then I would recommend Jonathan Stone's Phd thesis.
[0] https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Polyno...
[1] https://www.researchgate.net/publication/3334567_Performance...
Re: AT&T Fiber in the SF Bay Area is flipping bits
#103Trying to explain this issue to AT&T support is like trying to convince a doctor you're the only person on earth with a particular disease. Even explaining the issue is hard. It's not an outage, my internet isn't out , it's intermittently wrong . The phone support agents aren't prepared for this, and I can't find any way to escalate or speak to a network engineer. I feel like if I spoke to the right engineer, there'd…
[deleted]
Re: AT&T Fiber in the SF Bay Area is flipping bits
#104I had AT&T via Sonic's FTTN in an effort to avoid Comcast/AT&T directly, especially since Sonic does not have data caps despite running on AT&T's network and actually respects their customer's privacy. Unfortunately my experience was so terrible and unreliable that I decided to give up and finally sign up with Comcast, and just have to mind that 1.2TB data cap. The Bay Area of all places should not have such terrible…
I was seriously considering signing up for Sonic service, and I have Comcast now. Guess I won't do that. I hesitated because I really really hate AT&T. Guess I should have trusted that feeling.
Sonic's support is much, much better than AT&T's, FWIW.
If you must Comcast, at least make sure you Comcast Business so that you get connected to non-idiot support people.
Re: AT&T Fiber in the SF Bay Area is flipping bits
#105If you have AT&T fiber, run the script in the linked gist: https://twitter.com/bmastenbrook/status/1335400747794530304 It loads http://example.com and https://example.com and compares the result (should be equal) in a loop, and then reports if it finds a difference. I'm seeing multiple bit flips in the unencrypted version, and having a lot of issues loading web pages, presumably because a corrupted packet in a TLS ha…
All of these large companies seem to have (correctly) realized that 95% of tech support cases are trivial issues that can be resolved via automated responses.
The problem is that they then assume that all cases are one of those 95% in order to solve the 95% as quickly as possible, which probably looks good to whatever metrics they're tracking.
But if you're one of the 5% you're fucked.
If there's anyone out there designing tech support procedures, you should add an "is this a 5% problem?" question to whatever checklist you give to support staff.
Re: AT&T Fiber in the SF Bay Area is flipping bits
#106Trying to explain this issue to AT&T support is like trying to convince a doctor you're the only person on earth with a particular disease. Even explaining the issue is hard. It's not an outage, my internet isn't out , it's intermittently wrong . The phone support agents aren't prepared for this, and I can't find any way to escalate or speak to a network engineer. I feel like if I spoke to the right engineer, there'd…
I talked to somebody and he told me he had talked to his "IT department" and they're working on it but who the fuck knows.
Re: AT&T Fiber in the SF Bay Area is flipping bits
#107Trying to explain this issue to AT&T support is like trying to convince a doctor you're the only person on earth with a particular disease. Even explaining the issue is hard. It's not an outage, my internet isn't out , it's intermittently wrong . The phone support agents aren't prepared for this, and I can't find any way to escalate or speak to a network engineer. I feel like if I spoke to the right engineer, there'd…
The obnoxious thing to me is the hubris that must be behind this. Either they considered it and decided they would never encounter a system error like this and refused to implement an escalation route, or they never even considered it.
Or perhaps even worse than that, maybe they considered it, decided it was possible, but just don't care because of their insane borderline monopoly.
I don't understand how internet companies provide such consistently awful service.
Slightly off topic story, I've recently changed to another provider called Starry, and they force you to have a second router in front of your own router which they claim "decodes" their stream between the modem. I don't know the real reason but I'm pretty sure that's not it. If you plug their modem directly into a non-Starry router, the router just doesn't detect a connection.
One day, I tried to torrent something, and my internet would immediately get throttled to 0mbps. After investigating I found out that their router had a custom OS which hid a firewall and various security settings. Amusingly you could still access those settings if you just manually entered the page names into the address bar. Now all their stupid settings are disabled and I just feel badly for all the folks who use their service and don't have the savvy I do to actually get what they're paying for.
Re: AT&T Fiber in the SF Bay Area is flipping bits
#108Earlier quoted context omitted.
I am thinking the same problem. TCP checksum includes data field. Is it means AT&T flip bits and re-calculate checksum?
It looks like someone on the twitter thread checked and the checksums are wrong . Im not sure why these packets aren't discarded by your computer. edit: apparently osx doesnt drop these packets according to the twitter thread.
"It depends" - Your NIC could be doing some tcp offload for you, at which point any checksum you'd observe with tcpdump/wireshark would be flat out wrong.
Generally - both the tcp checksum and the 802.11/Ethernet CRC isn't all that strong, so it's entirely within the realm of possibility of having bitflip patterns that fool both.
Re: AT&T Fiber in the SF Bay Area is flipping bits
#109If you have AT&T fiber, run the script in the linked gist: https://twitter.com/bmastenbrook/status/1335400747794530304 It loads http://example.com and https://example.com and compares the result (should be equal) in a loop, and then reports if it finds a difference. I'm seeing multiple bit flips in the unencrypted version, and having a lot of issues loading web pages, presumably because a corrupted packet in a TLS ha…
Oddly, I can't even resolve example.com (using AT&T DNS).
Re: AT&T Fiber in the SF Bay Area is flipping bits
#110Wow. I happen to setup my PiHole at the same time and did not expect it to be the ISP. I even bought the newest RPi 4 and disabling lists without any luck. The interesting part is that I turn off my wifi on my cellphone if the site load hangs and it always worked. I always thought it was because I was using my non-pihole DNS.