Princeton and iOS DHCP still not getting along
It seems that every time Apple squashes one DHCP bug in iOS, another one pops up.
Dynamic Host Configuration Protocol (DHCP) is a system of automatically assigning IP addresses on a network, which mostly happens behind the scenes and without users noticing anything about it. Without an IP address, a device such as an iPhone, iPad or any sort of computer cannot access the network.
DHCP uses a "lease" system where a computer can use a specific IP address for a certain length of time. In contrast to a static addressing scheme (where each device has a permanently-assigned IP address), DHCP allows many more devices to use the network -- as long as they are not all online at the same time.
Initially, iOS devices had two different problems. First they would hold on to their IP addresses after the "lease" expired, when they were supposed to be done with them.
Apple apparently fixed that problem, but created another one: devices were asking to renew their DHCP leases too often. The latter problem was fixed in iOS 4.1, but that was only released for iPhone and iPod touch devices, not iPads. With iOS 4.2, that bug is finally fixed.
But don't get too excited.
According to Princeton's tech team, the latest versions have a problem that they're listing as "iOS 4.1 - 4.2.1 Allows DHCP Lease to Expire, Keeps Using IP Address." Does that sound familiar? It's eerily like the earlier report from Princeton, "iPhone OS 3.2 on iPad Stops Renewing DHCP Lease, Keeps Using IP Address" -- so the issue is not taken care of yet.
If you only use your iOS device on a small home or office network, you may not be aware of this flaw, but -- and I hate to have to be so obvious, but a lot of people have apparently missed this -- managing a computer network on a university campus is a whole lot different than your home Wi-Fi network.
Despite reports, Princeton has not "banned" iOS devices, but their workaround includes disabling Notificatons, Find My iPhone/iPad, FaceTime and removing all VoIP applications.
Hopefully, Apple will figure out how to get the iOS DHCP client to work efficiently on larger networks one of these days. In the meantime, you can keep track of the issue on Princeton's Apple iOS Networking page.
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It seems that every time Apple squashes one DHCP bug in iOS, another one pops up. Dynamic Host Configuration Protocol (DHCP) is a system of...
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I had the EXACT DHCP issue with my College and GNU/Linux .
In the end I got my own Web from the cable company . and in hind sight Iam glad I did . Ends up our Entire College runs on 35Mbps bandwith . and this is spread over a student population of over 4000.
my little 10 Meg cable is now worth a ton more .
last week before the break they upgraded the routers and APs and from what I have heard there now compatable ..
its sad that what is a STANDARD is so hard to comply with ..
frankly I personaly think the guys in IT NEED to do tests with there gear before they deploy a campus wide rollover of gear .
if they Cover WIN MAC GNU/LINUX and IOS ANDROID PALM and Win Moble there covering 99.97 of the devices out there..
I work at a university with DHCP on a network and have not seen these problems. Each weekday, I'm logged in on my iPhone and iPad, both of which have been updated regularly. In fact, the IT folks in my department are currently testing iPads for regular use; thus far, there have not been connection issues. Of course, there are many different configuration and potential issues, so my lack of troubles does not negate real issues. Simply stating that DHCP does not have across-the-board issues in iOS.
December 19 2010 at 8:33 PM Report abuse Permalink rate up rate down ReplyIt seems that Princeton has similar issues with Android as well: http://www.net.princeton.edu/android/
It is absolutely FALSE that "DHCP allows many more devices to use the network" as the article states. The number of devices able to connect to the network is limited by the number of available IP addresses in the subnet (and allocated for DHCP or static networking). DHCP just facilitates the process of IP address assignment by handing them out automatically instead of the user having to be given one that is reserved for you in some manual fashion. But in the end, it doesn't magically let more users on the network. The number of devices able to use the network would be the same either way.
December 19 2010 at 12:47 PM Report abuse Permalink rate up rate down ReplyNo crazy admins at work here. I've seen this on the corporate network at my workplace as well. Cycling wifi off/on seems to fix.
December 19 2010 at 11:54 AM Report abuse Permalink rate up rate down ReplyI think Princeton needs to hire some admins that are a bit more experienced with OS X. This is a common behaviour with OS X and is NOT only an iOS problem. If you suspend an OS X computer, say you just close the lid of your macbook and then while it is suspended another device starts using the same address because the DHCP reassigned it, you will get an error message next time you open your computer. The message reads something along the lines that the IP address is being used by another device on the network. Apple decide to reduce the load of DHCP servers by not running an IP release/renew every time you come out of low power mode. And if you really get problems with DHCP I would bet that 9 out of 10 times it is the administrators fault for trying to micromanage the DHCP cycle too closely.
December 20 2010 at 5:10 AM Report abuse Permalink rate up rate down ReplyIf you read the linked article on Princeton's networking site, you can see the exact situations in which the bug manifests itself.
December 19 2010 at 10:33 AM Report abuse Permalink rate up rate down ReplyThey are clearly misusing DHCP because all the reports have to do with not properly dealing with devices not renewing... and they used 3/6 hours as an example. Way to short for "student" devices, probably due to lack of enough addresses for all the new devices hitting the network. I'd also think that they're reusing the IPs too quickly.... probably in an effort to break P2P... which is exactly what Push Notifications are. I almost think there's some "social engineering" going on to cut back incoming traffic... ie make things they don't like "break a little bit." I'll admit my IT department does it all the time.. but they own upto it.
I can see the issue, the iDevices are mobile, so they should track across campus. Apple dialed down the DHCP requests because if they followed what Princeton is asking to refresh for every "push" update "just in case", they get what 'mb' was reporting, that the device keeps gathering IP addresses from 20 access points 40 times a day and not giving them back.
All it takes is one crazy network admin who thinks he's all that and a bag of Fritos to totally screw up a network and then blame problems on new devices like the iPhone or iPad. Oh sure, the Genius admin at Princeton is not to blame, it's those naughty iPads! Heck, I work for a Fortune 100 company, we can't seem to get our DNS servers to update properly either...
Why is it only Princeton having all these issues? How the heck are they configuring things on their network that make it more susceptible to these DHCP problems?
I wouldn't be surprised to hear the made a mistake similar to one made at my company. When a recent change in DNS/DHCP systems was made they imported all the data from the old system and filled in some defaults for missing values. I personally found and pointed out a misconfigure they had on every single subnet in the company: The lease time for IPs was set to a value (usually 3600 for the subnets I was on) but the renewal time was set to 28800. From what I found online (and through testing) if the renewal time field isn't set then DHCP clients will assume renewal time is 1/2 lease. But (and here's the issue) if the renewal time field is set, the client assumes it's valid and uses it. When you have the kind of mismatched values like we had, you end up with problems exactly like what they're describing at places like Princeton. The DHCP client is then just doing what it was told and isn't renewing until the time the field was set to.
December 19 2010 at 2:06 PM Report abuse Permalink rate up rate down Reply"It seems that every time Apple squashes one DHCP bug in iOS, another one pops up" ... at Princeton at least. Unless we're to believe that very other major entity with a DCHP network keeps quiet about the problem, it is odd how many problems Princeton has. Do a little research on the last three times that Princeton's 'tech team' reported on this issue and see how many commentators noted the conspicuous lack of trouble elsewhere.
It is "eerily like the earlier report"(s). Perhaps eerily isn't the best description.
Rather suggests that iOS might not be the issue, but rather their software/hardware.
December 19 2010 at 2:42 PM Report abuse Permalink rate up rate down ReplyMy iPad was fine with iOS3 but I'm having to constantly renew the DHCP list with iOS4 and I'm on a regular, everyday home wifi network which my iPhone 4 has no problem with. Wrote to Apple weeks ago but no response...
December 19 2010 at 9:11 AM Report abuse Permalink rate up rate down ReplyMy iPad & iPhone are doing fine on 4.2 but I'm using an Airport Extreme Router at home. They also work fine with a generic dsl router at my office.
December 19 2010 at 9:22 AM Report abuse Permalink rate up rate down ReplyI am having the same issues at Monmouth University, the lease keeps needing to be renewed and sometimes I can't even access the internet or "re-login". Its almost like I am banned from using their wireless network for 10 minutes. Maybe Princeton has this same issue, it needs to be resolved as soon as possible, its very inconvenient.
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