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

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354 points timdoug | 9 comments | 12 Jul 11 17:04 UTC | HN request time: 0s | source | bottom
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th0ma5 ◴[12 Jul 11 19:40 UTC] No.2756182[source]▶
"This whole notion of being so proprietary in every facet of what we do has really hurt us." Steve Jobs, circa 1997
replies(1): >>2756426 #
1. bradleyland ◴[12 Jul 11 20:34 UTC] No.2756426[source]▶
There is nothing proprietary about this.
replies(1): >>2756667 #
2. th0ma5 ◴[12 Jul 11 21:26 UTC] No.2756667[source]▶
Do you have any examples of other vendors using the last assigned address as a default?
replies(1): >>2756752 #
3. intranation ◴[12 Jul 11 21:47 UTC] No.2756752[source]▶
Proprietary in the computer sense is generally taken to mean closed source or at least not made available to competitors or others. There's nothing to stop any other systems offering this kind of quick start DHCP service.
replies(1): >>2756788 #
4. th0ma5 ◴[12 Jul 11 21:56 UTC] No.2756788{3}[source]▶
Except that it violates the specification right? I guess we're agreeing to disagree on the definition of proprietary. I can buy all of Apple's funky connectors through various suppliers, and maybe even fab them myself, but to me they're still proprietary. Sorry to be pedantic!
replies(1): >>2757162 #
5. __david__ ◴[12 Jul 11 23:55 UTC] No.2757162{4}[source]▶
Which specification does it violate?
replies(1): >>2757196 #
6. th0ma5 ◴[13 Jul 11 00:08 UTC] No.2757196{5}[source]▶
rfc 2131? seems to say the client can ask for an unlimited lease, but the server can specify a finite one. this article seems to be saying that this thing will use the last one leased no matter how long it's been off the network
replies(1): >>2757498 #
7. bradleyland ◴[13 Jul 11 02:07 UTC] No.2757498{6}[source]▶
The DHCP client acts as expected. The behavior observed by the post author occurs before DHCP negotiation executes. I know this seems like a technicality, but it's the truth. The sniffing and assumed use of an IP address occurs outside the DHCP request/response cycle. It's used ahead of time, and discarded if the DHCP 'request' request is denied.

The only people bent about this are people who have any idea what's going on behind the scenes. In the rare cases where this is a problem, the issue is quickly resolved. If this were a "real" problem, we'd have seen a lot more issues by now. The Apple discussion boards would be lit up with complaints. They're not. This is a non-issue. Only pedants are stuck on the fact that there's no RFC for it.

replies(2): >>2757613 #>>2759734 #
8. th0ma5 ◴[13 Jul 11 03:10 UTC] No.2757613{7}[source]▶
hrmmm! good point, i assume too much, and i guess i assumed in the cadence of 802.11 whatever, dhcp comes next because it always does, but it never has to! and apparently not here for a moment. thanks for coming back to post this.
9. simmons ◴[13 Jul 11 17:31 UTC] No.2759734{7}[source]▶
And as several people have pointed out to me, it looks like there is indeed an RFC for it: RFC 4436, Detecting Network Attachment in IPv4 (DNAv4).