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CenturyLink 911 outage was caused by a single network card sending bad packets

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Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#41
post #21

How does a single network card emitting bad packets effect other sites? > investigations into the logs, including packet captures, was occurring in tandem, which ultimately identified a suspected card issue in Denver, CO. Field Operations were dispatched to remove the card. Once removed, it did not appear there had been significant improvement; however, the logs were further scrutinized .. to identify that the source…

Every time it comes to “root cause analysis” (quoting makes sense in this context) I think of https://www.kitchensoap.com/2012/02/10/each-necessary-but-on...

The quality of the outcome really depends on the participants. As they say, blaming the humans is easy. But it’s not five why’s.

There are lots of proximate reasons that a failure can avoid all of your sanity checks, but the simplest is when your organization is a little insane. I try to steer the conversation toward avoiding surprises, other times toward ergonomics (don’t rely so much on humans in the moment to do the right thing).

Often people don’t fight me too much on that, but sometimes it’s a near thing. Lots of senior devs are senior because they keep everybody else down, so blaming human error for an outage seems perfectly reasonable to them.

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#42
post #11

Wonder how they found it... I bet that was some unhappy hours looking for it.

That's the "I found a 15-year-old bug in our NIC" story that I'd love to read but which will probably never be told. And whoever designed the system is busy obfuscating that on their resume this morning.

I's more likely the card went rogue and failed.

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#43

I was visiting my SO's parents in Portland for the holidays when this happened. Their cable TV stopped working for at least two days and we all got an emergency services text with the local emergency number because 911 wasn't going to work. (At least their Internet through CenturyLink remained working.) This also happened to coincide with them receiving a notice of a $50/month increase on their bill from CenturyLink,…

To be fair, this does seem like an extremely rare root cause, but yes the impact was awful, so it'll be worth noting how CenturyLink responds and what they'll do to try to prevent similar issues in future.

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#44
post #40
post #39

Earlier quoted context omitted.

At least in my area Century Link business is the only isp I can get at my house that doesnt come with a data cap. Both CenturyLink home and our cable provider have data caps that are enforced. And working from home along with Netflix and YouTube blow me through the 80gb limit every month. Causing me to have to raise my plan. And I’m not paying $200 a month for unlimited bandwidth.

Your cable options have an 80gb limit?! WTF!! Comcast has data caps (which is stupid) but it's 1TB and I think my 7 person household has only passed the halfway mark once, so it's meh. But 80GB?! That's insane! Destiny 2 is an 80GB download itself.

This is why amazes me. At my home we blow through on average 25 GB a day in gaming, streaming video, other downloads etc. limits like these are terrible. 80 a month? Wtf?!

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#45
post #43

I was visiting my SO's parents in Portland for the holidays when this happened. Their cable TV stopped working for at least two days and we all got an emergency services text with the local emergency number because 911 wasn't going to work. (At least their Internet through CenturyLink remained working.) This also happened to coincide with them receiving a notice of a $50/month increase on their bill from CenturyLink,…

To be fair, this does seem like an extremely rare root cause, but yes the impact was awful, so it'll be worth noting how CenturyLink responds and what they'll do to try to prevent similar issues in future.

At scale, rare errors will occur on a semi-regular basis.

Multi-day outages tend to be indicative of a dysfunctional internal organization.

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#46
post #2

They’re now filtering bad packets so this can’t happen again. No mention of fixing the design flaw in the system that allows a single piece of malfunctioning hardware to knock out 911 service for millions of users for two days .

Worth giving some credit though - mitigation is important for something as critical as 911 service.

Hopefully they're also tracking the design flaws, and yes that's worth following (and asking whether they're planning to do so?), but bear in mind people have limited time and resources, so don't be too hard on them (or they'll be less willing to help and investigate in future).

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#47

I was visiting my SO's parents in Portland for the holidays when this happened. Their cable TV stopped working for at least two days and we all got an emergency services text with the local emergency number because 911 wasn't going to work. (At least their Internet through CenturyLink remained working.) This also happened to coincide with them receiving a notice of a $50/month increase on their bill from CenturyLink,…

Just deciding they want to put it up 50 dollars a month is insane!

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#48

Earlier quoted context omitted.

Honestly, if you had FiOS as an option why would you stay with CenturyLink in the first place? Verizon is just as assholish, but at least they can deliver.

centurylink fiber is pretty great as well

Yeah, my experience with Clink's fiber offerings has been a good one. It's definitely "Gigabit" — there are many fiber splitters in play, which means (a) your downstream traffic is broadcast to everyone on the same splitter network in plaintext and filtered at individual ISP-owned termination devices, much like cable networks, and (b) you definitely never reach 1000 Mbps down, but often can reach 900 Mbps up. Typical is 500-600 Down, 900 Up; the highest I've seen down on e.g. fast.com is 900 Mbps. And the price is extremely competitive with Comcast ($80/mo for "gigabit"), unlike their DSL offerings, which are complete crap.

The major downside is that their IPv6 support is nonexistent and they have no plans for rolling it out.

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#49
post #38

Earlier quoted context omitted.

They generally only get dropped if they have an invalid checksum. Since checksums are hardware accelerated, the invalid packet probably had a valid checksum applied to it.

If cut-through is enabled in the switch, it won't even drop on bad checksum, since by the time the switch can tell the checksum is wrong, it has already forwarded the entire packet.

It is really unfortunate that the checksum is on the opposite end of the frame from the routing information on Ethernet frames.

Re: CenturyLink 911 outage was caused by a single network card sending bad packets

#50

Earlier quoted context omitted.

Honestly, if you had FiOS as an option why would you stay with CenturyLink in the first place? Verizon is just as assholish, but at least they can deliver.

centurylink fiber is pretty great as well

Here in Denver we get full 1Gbps for $75/mo, every provider has outages and this was the first partial outage we experienced with the service (pages loaded just slowly most of the day)
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