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Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

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Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#81

Post by sethammons »

> I assume the Mac would know to begin the DHCP discovery phase, instead of sending blind requests for a former IP address...

I wonder if that is my problem. Often, my Mac won't connect to my mobile hotspot. I open the lid, it starts attempting to connect to the hotspot and just sits. Connecting. Forever. I can turn off WiFi, turn off the hotspot, and sometimes even reboot both my phone and my laptop and still be unable to connect.

I recently figured out that if this not-connecting happens, I can disable wifi, disable hotspot, turn on WiFi and select my not-on hotspot to connect to. A couple of seconds later, it fails and asks to run network diagnostics. I cancel, disable wifi, turn back on the hotspot, turn back on wifi and, presto, it connects.

I figured there was some caching going on and that I am effectively invalidating the cache. Maybe this is what the op is talking about here.

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#82

Post by johncolanduoni »

dspillett wrote: post #70
pilif wrote: post #52

Earlier quoted context omitted.

In this specific case, the DHCP server configuration under Windows makes it abundantly clear though that you need to make your DHCP server authoritative by adding a warning icon and presenting a warning dialog when it's not running in authoritative mode. Making it authoritative is then to just press a button in that dialog. Yes. You have to know that you have to open the GUI for DHCP server configuration in order to…

> the DHCP server configuration under Windows Though for the opening to the current discussion that is a moot point - this is not relevant to either OS on the desktop .

Neither Windows nor Linux desktops buck the trends (with respect to documentation and user expectations) that their server counterparts follow.

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#83

Post by djrogers »

sethammons wrote: post #81

> I assume the Mac would know to begin the DHCP discovery phase, instead of sending blind requests for a former IP address... I wonder if that is my problem. Often, my Mac won't connect to my mobile hotspot. I open the lid, it starts attempting to connect to the hotspot and just sits. Connecting. Forever. I can turn off WiFi, turn off the hotspot, and sometimes even reboot both my phone and my laptop and still be una…

It sounds more like your hotspot is janky - if a Mac doesn’t get a DHCP response it will still connect to the wifi network using and autoconf address. There is no dhcp related scenario that causes it to not connect to the network at all.

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#84

Post by djrogers »

3pt14159 wrote: post #65
kalleboo wrote: post #10

I remember this feature used to cause a lot of problems with random IP conflicts, but I haven't had an IP conflict like that in years, so it seems they've made it a lot more robust. Or are routers/DHCP servers just less broken these days (I guess since Apple's market share has forced them to)?

It still happens. I run Ubuntu on a MBP (dual boot) and some networks are fucking great. No problems whatsoever. Others I get booted off more frequently the more people enter the cafe. I dug into the problem a while back and figured out it was this shitty behaviour by Apple that Ubuntu hadn't fixed.

It’s not a Mac hardware behavior, it’s in macOS - the fact that you’re seeing bad things in Ubuntu has nothing to do with Apple here.

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#85

Post by djrogers »

mschuster91 wrote: post #50

The joke is, Macbooks are dead slow on WPA2-Enterprise networks once you go with certificate-based logins. At home, I'm in the network often enough faster than 1s - at work, up to two minutes sometimes. I guess that modern macbooks keep the connection alive on the PHY level while asleep... they do have that "backup/sync while you sleep" feature, so quite possible that the chip handling this feature only speaks "norma…

If you’re seeing 2 minute connection times that’s on your network - probably the RADIUS server, not macOS. There are tons of places using macs with WPA2 and certs that don’t have any connection lag - including my employer and many of my customers.

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#86

Post by rektide »

bobsam wrote: post #71
epistasis wrote: post #11

This is an article from 2011, 6 years ago. Has there been any progress on implementing RFC 4436 on Linux in general or Android specifically in the interim? http://www.ietf.org/rfc/rfc4436.txt

No, but it is still quite fast. On chromeOS network bring up is extremely fast. We are talking 1-3 seconds from cold boot to your emails have been synchronized. My Ubuntu is almost as fast, if we subtract the 4 seconds the ugly bios screen adds. No idea about Android, but did you read the end of the article?

My NetworkManager still takes multiple seconds to connect to wifi, and that's definitely the same pathetic DHCP behavior. wpa_supplicant is super fast. Modern Ubuntu (17.04) is still stuck in this ancient, lethargic world.

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#87

Post by ksk »

Interestingly, we use Cisco's Meraki APs at work. The WiFi is pretty solid most of the time, but macs are the only machines that suffer occasional dropouts and then DHCP stops working till you cycle the n/w adapter. (though iphones never seem to have this issue).

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#88

Post by mdekkers »

wtfwtfw wrote: post #28
mdekkers wrote: post #24

Earlier quoted context omitted.

As I was reading, I was mentally composing a convoluted reply. Yours said the same thing, much better, and bonus coffee over my screen! well done :)

> bonus coffee over my screen Why did you pour coffee on your screen? That's really quite strange behaviour.

HN isn't in the mood for levity today....

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#89

Post by mdekkers »

acdha wrote: post #74
mdekkers wrote: post #26

Earlier quoted context omitted.

My SO unfortunately has 2 ipones, an ipad and a MBP. There is a confluence of DHCP activity from all these devices that is guaranteed to take my network down.

Unless your DHCP server is an old Commodore 64, that's not the right diagnosis. The ISC DHCP server was rock solid with negligible CPU load with many thousands of clients even 10-15 years ago. If your network is really having problems, either dig deeper if you want to learn more about networking or buy something like a Google WiFi device if you just want something known to handle much greater loads without issue.

It will kill my fiber to the home network box that my telco installed, and provides DHCP. It isn't a load issue, it is a "the DHCP server died" issue.

Re: Rapid DHCP: Or, how do Macs get on the network so fast? (2011)

#90

Post by mdekkers »

pilif wrote: post #56
mdekkers wrote: post #26

Earlier quoted context omitted.

My SO unfortunately has 2 ipones, an ipad and a MBP. There is a confluence of DHCP activity from all these devices that is guaranteed to take my network down.

DHCP activity from 4 devices will not slow your network, much less take it down. A DHCP negotiation to get an IP address takes 4 UDP packets, all of them usually below 500 bytes in size. Not even when you have set the lease time to the theoretical minimum of 1s, this traffic will be at all significant in your network.

It will kill my fiber to the home network box that my telco installed, and provides DHCP. It isn't a load issue, it is a "the DHCP server died" issue
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