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Comment by lucb1e | Hacker News Reader

> I mean who would know just how long a MAC address is?

Uh, my main languages are PHP and Python (high level stuff) and I'm a student (not someone with 10 years of experience) but I knew that. 3 bytes for the vendor block, 3 bytes for the device.

> Or what the actual SYN/ACK etc tcp flags are?

Yeah the actual bytes, who ever uses that? A MAC address I've seen plenty of times in my life as hex, and I've seen the TCP setup flags being exchanged plenty of times in Wireshark and looked up the hex once when I was implementing TCP from scratch, but I still wouldn't expect anyone to know that.

> You just need to know what they're used for

Agreed on that. I wouldn't blame anyone for not knowing the size of a MAC address, I just didn't think that one is that obscure.

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> I'm a student (not someone with 10 years of experience) but I knew that. 3 bytes for the vendor block, 3 bytes for the device.

That is why you know the answer. Come back in 10 years and let us know if you still know it. What you think might be mainstream in a computer science class are rarely used in application. And if they are they can be easily looked up.

I used to know the exact effective distance of a CATV cable when I was a student. Useful? Sure. Something I need to remember for the rest of my life? Definitely not.

As another example, in 17+ years writing ISO level 7 programs, I have never once needed to use the Mac address.

> Come back in 10 years and let us know if you still know it.

I've never taken a CS class, and I still know it. I've just stared at enough packet dumps and debugged enough issues that it happens to stick.

I think it's a stupid question to ask as a screener, as it tests familiarity with trivia. It's the kind of thing I'd be happy to see that somebody knew, but it's never something I'd downcheck them for not knowing. It could just mean, as in your case, that there deep knowledge is somewhere else.

> I've never taken a CS class, and I still know it. I've just stared at enough packet dumps and debugged enough issues that it happens to stick.

We are all a product of our environment. And there is certainly a chance in 10 years the OP will still know how many bytes are in a MAC address. I only mentioned computer science based on the "student" part of the quote.

Personally I've been spoiled by working on higher level stuff so if I do look at a packet dump I usually filter the packet headers out. But again, we're a product of our environment and asking questions that a reasonable skilled engineer might go their entire career without knowing the answer to except in that interview is a bit suspect and will likely disqualify people that would be otherwise great for the job.

This reminds me of the time when I liked physics very much. I used to memorize 10 digits of speed of light and feel very proud.

I don't have the length of a MAC address memorized (because why would I need to?), but I know what one looks like, so I can pretty quickly work it out in my head. A hex digit is four bits...

Maybe 10 years from now I'll have forgotten everything about the hex/binary/octal representations of numbers, but I certainly hope not!

> What you think might be mainstream in a computer science class are rarely used in application.

Uh actually my classes didn't teach me that. Side projects did.

Kudos to having side projects. That's awesome.

The point still stands though. First, it is much easier to have side projects when you are in school so the causal relationship might still be there just one step removed. But the more important point I was making was that school or a side project or even a project at work, if people go 10 years without using it, they forget things.

As an aside, you may want to drop the "Uh" in-front of your sentences. It conveys a certain tone that I'm not sure you are doing intentionally.

> Uh, my main languages are PHP and Python (high level stuff) and I'm a student (not someone with 10 years of experience) but I knew that. 3 bytes for the vendor block, 3 bytes for the device.

Thanks for the refresher! I knew that too when I was in college. Good luck remembering that 5 years from now :)

Still know that 20 years down the line, but then I do networking stuff routinely. If the candidate was interviewing for anything network related (the article is down atm), it's fair game.

Thanks for the snarky remark.

I did not learn this because some course demanded I learn a text book by heart. I'm not doing that kind of theoretical university. I knew that particular thing because I look at a lot of packet captures.

Yeah, you're a student; you probably just took a class on this stuff. You'll forget it soon enough if you don't use it.

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