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justin
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Apple AirPort Extreme (2011)

justin

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Windows wireless dhcp quirks and hassles

I've had lots of experience with roaming to different wifi networks, and it isn't perfect.

1. taking a long time to pull an IP.
Sometimes when I un-suspend in a known open wifi spot, the whole process of getting a new IP takes ages. By ages I mean, 10 seconds or more .. It should be nearly instant.. neither end has to do much work here!

2. Taking time to pull an IP
Even if it is fast, it still takes 4 seconds. What on earth takes 4 seconds of compute time over an established wifi connection with 1ms latency and no security? (If I release, then time /renew, it takes that long to complete).

3. working for a few seconds then getting a new IP:
Sometimes instead of taking a while, opening up in a previously used hot-spot the connection works for a few seconds then suddenly it is re-cycling and "acquiring IP address". This means you get a couple of pages off and then boom: you're kicked and waiting for renewal again. If the previous lease expired already, why did windows try to use it? why did the router respond? Are leases remembered per hotspot? If the lease didn't expire, why did it get kicked?

Is there any debug log or anything that reports what is going on under the hood with DHCP under XP? it is frustrating to see the spinning globe and have no clue: is it failing to get packets from the router, is the router replying "no"? and when I it goes back for more later during the session, why is that, did the lease expire?

I probably use about a dozen wifi spots regularly, and have used another two dozen. They obviously use a variety of wifi routers. I get these hassles on all of them, to a greater or lesser..

No_Strings

join:2001-11-22
The OC

1 edit

No_Strings

Justin,

What h/w is the wireless card?

Assumed, but to verify: Are you using XP to manage the card vs. the manufacturer's utility?

Any anti-malware products loaded/running?

circle
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Appleton, WI

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to justin
Is this a correct understanding of your situation?

You use a hotspot, hibernate/suspend your laptop, go to a different hotspot and then come out of hibernation / suspension. Your laptop then takes some time in reestablishing a valid IP address at the new hotspot.

If this is the case, it is normal operation. Each DHCP server that you pull an address from must verify with the client that it has a valid IP and that the lease is still good. Hotspot A’s DHCP server knows nothing about Hotspot B’s DHCP server.

justin
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join:1999-05-28
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Apple AirPort Extreme (2011)

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It is native XP (zero config service etc), I tried the intel software package and found it awful and huge as well with half a dozen flaky services. Nothing installed on the laptop especially not av or anti malware or firewall.

To circle See Profile .. I suspend then come out and the connection to the new hotspot is established pretty fast, but no dynamic IP is obtained quickly & various quirks I describe can happen after that. Or, I suspend, then re-establish within the same hotspot, and get the "Works for 2 seconds then dies and refreshes the lease" delay.

Obviously hotspot DHCP servers know nothing about each others leases but then this is a windows issue: If I change hotspots (which windows knows) windows should not try to re-use any bad information such as an invalid lease or IP it carried over from the last hotspot.

Oh, and another problem, if I have 'linksys' as an automatic hotspot (as one sometimes does), and lose connection to my primary hotspot, even though signal is great, it falls back too easily to trying to talk to the distant hotspot (linksys) even though the local hotspot is currently showing a much stronger signal. I then have to manually disconnect 'linksys' and manually request reconnection to the local strong spot.

And either way, the process of release/renew should take less than second. Why does it take anywhere from 4 to 10+ seconds to obtain a new lease? that is a bizarre waste of time is not inherent in the DHCP protocol.

So where do I get a log of what the windows standard dhcp service is doing inside the laptop at each step? all I know of is ipconfig /all which shows the lease time and expiry time, but of course that is totally insufficient.

Maybe I'm being unreasonable and this is just a rant.

I don't think many people use as many different hotspots as I do on a regular basis, perhaps this whole wifi roaming thing is flaky under XP (without carrying around a mac or dual booting to linux I won't know for sure) and different wifi routers have quirks as well (a surprising number of popular consumer wifi routers quietly flake out and reboot themselves on a regular basis).

This stuff has been around for years now, it should be instant and seamless, but it is flaky as hell - at least compared to (say) how cellphones switch from tower to tower. People appear to be satisfied if they get a solid signal with no packet loss for several hours, as if that is any accomplishment.

I get mad every time I watch it "acquiring an IP address" I want to shout at it: WHAT the HELL are YOU DOING RIGHT NOW that takes SO MANY CYCLES? Since the delay is right there between "release" and "renew" it isn't anything to do with drivers getting unloaded or shutdown or cards warming up or whatever. My best guess is there are bunch of crap code perhaps on both ends that works with stupid timeouts, polling, and other delays..

No_Strings

join:2001-11-22
The OC

No_Strings

Intel drivers have been the source of many headaches in this forum. The consensus seems to be that the latest are much improved, so I'd start there.

My personal experience is that no O/S - BIOS - driver combination reliably handles networking, least of all wireless, after waking from suspend or hibernate. I don't even try anymore. Even if it works 9 out of 10, the tenth event will be so aggravating as to make the nine not worth avoiding a reboot.

justin
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Apple AirPort Extreme (2011)

justin

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I don't use hibernate, it is greyed out under XP because of a failure that I see lots of people google about but no easy fixes, something about unable to complete the API due to "insufficient resources". So I'm down to only suspend/resume.

It definitely works after suspend but I really don't think the _whole_ dhcp quirks thing is related to the fact it was suspended them came back. Maybe one problem can be pinned on that. I'm not prepared to give up the convenience of suspend/resume to debug dhcp anyway. Getting shafted with a cold-boot to get relief from hassles with holding onto a good IP isn't worth it.

Eh, maybe I'll try ubuntu, and see if I get the same drama.

I could try the newer intel drivers but I'm afraid. Last time they wouldn't un-install. I was killing stupid processes and looking for files to delete so they couldn't be run, for weeks afterward.

cacroll
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said by justin:

It is native XP (zero config service etc), I tried the intel software package and found it awful and huge as well with half a dozen flaky services. Nothing installed on the laptop especially not av or anti malware or firewall.

This stuff has been around for years now, it should be instant and seamless, but it is flaky as hell - at least compared to (say) how cellphones switch from tower to tower. People appear to be satisfied if they get a solid signal with no packet loss for several hours, as if that is any accomplishment.


Your cellphone works on a cellular network. Each cellphone AP is carefully setup, to interoperate with other APs in that network.

Your WiFi computer works (somewhat) on individual APs, no network there. The AP at StarSmucks has no interoperability with the AP at MarriottIntl, or at MikesIndependent. To say nothing of MyAPHandsOff.

The problem with "Linksys" is by design. Roaming lets you switch between APs with the same SSID. If you pick a common SSID as your preferred target, when you move from location to location that SSID will be picked.

What happens if you actually shut down and restart?

justin
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justin

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It is hard to debug a problem with delays. eg, the network is fine now, so if i restart, does that test anything? these quirks strike randomly.

cacroll
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cacroll

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said by justin:

It is hard to debug a problem with delays. eg, the network is fine now, so if i restart, does that test anything? these quirks strike randomly.


If you're not having any problems, restarting probably won't fix anything. I'd try a restart the next time the problems start though.

Do you see any pattern? Any specific hotspot when you have problems, any specific hotspot that you just came from when you have problems? Time of day? Day of week? Other people at hotspot? Brand of AP?

justin
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justin

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It is fairly random..
For instance: I came home with the suspended laptop and opened up at home and instead of getting an IP I got a spinning acquiring IP thing, then, after a long pause, the little yellow warning triangle appeared. I just sat and left it, and probably 30-60 seconds later it sorted itself out. I find that outrageously wrong. Even if it doesn't recognize time has passed (from the suspension) it knows that it can't find the old hot spot anymore AND there is a new auto-connect hotspot available at full strength. Even if DHCP servers are slow it could know what to do, instead it seems to go through several time outs.. and a hissy fit to boot.

I'm probably expecting too much. It is wrong to expect wireless connectivity to just work. There aren't any wires, right? so it clearly needs to be difficult and finnicky. Sigh.

Bill_MI
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Bill_MI

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Lovely, isn't it? I've been wondering for ages how people have put up with Windows DHCP since it tends to behave exactly as you describe. Not just wireless - plugging ethernet is the same, wireless is just another way to plug into a network.

I don't even have XP - but you describe NT3.0, NT3.5, NT4 and NT5 (Win2K) perfectly. It takes far longer than it needs to 1) Convince the client the old DHCP server isn't there! 2) Make sure nothing else already has some new address before it's issued. 3) Schedule network operations inside the stack.

It's often faster to set a static IP... and I DO use static IP at known locations on wireless. It works great.

cacroll
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It's a bit more complex than DHCP. Before DHCP enters the picture, it has to involve WiFi. Hopefully, your home SSID is a bit more unique than "Linksys", but if it was something not completely unique, then the laptop might be trying to roam.

Have you tried unsuspending, then turning the radio off and waiting until the network drivers realised that it was off, before turning it back on? I've done that with mine once or twice, and usually when returning home as you are doing.

justin
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justin

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I'm trying the latest intel driver now, which supposedly fixes a roaming "issue" (they are a bit vague in describing it). We'll see.

But irrespective of the intel driver or whatever, why is it unreasonable to expect DHCP to work at high speed?

At the coffee place I did a /release .. /renew and it took 5 seconds. Outrageous, but still, read on. I just tried it at home (bog standard verizon westell router), and the same sequence .. release .. renew .. took a full 30 seconds. /renew without /release is almost instant, and DOES renew the lease according to /all.

Wireless isn't even involved here, it must stay connected during this, I'm just fiddling around on the layer above.

cacroll
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cacroll

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said by justin:

I'm trying the latest intel driver now, which supposedly fixes a roaming "issue" (they are a bit vague in describing it). We'll see.

But irrespective of the intel driver or whatever, why is it unreasonable to expect DHCP to work at high speed?

At the coffee place I did a /release .. /renew and it took 5 seconds. Outrageous, but still, read on. I just tried it at home (bog standard verizon westell router), and the same sequence .. release .. renew .. took a full 30 seconds. /renew without /release is almost instant, and DOES renew the lease according to /all.

Wireless isn't even involved here, it must stay connected during this, I'm just fiddling around on the layer above.


How is wireless not involved? Are you using Ethernet to connect when you get home?

If a release - renew at the coffee place takes 5 seconds, and at home it takes 30 seconds, isn't it possible that the equipment at home is part of the problem? Not just Windows and the laptop drivers?

Wireless doesn't just stay connected, when you move around. When you move from one AP to another, there is hand offs, and wireless is indeed involved. Maybe the WiFi client manager, and you having to reselect another AP, isn't involved, but I bet wireless is involved somewhere.

justin
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justin

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What i mean is that a release/renew does not tell the wireless card to disconnect from the AP, then reconnect. There is only one AP during my release..renew commands, it has link all the time. It is just that between release and renew I have no IP and can't do anything except issue DHCP broadcast packets.

My home router is the westell that every other verizon user gets, millions sold. It might have an issue with its dhcp server but then every other person has the same issue, plus I see this delay at random hotspots using a variety of equipment. Not always 30 seconds. Sometimes 5 seconds, sometimes 30 or in between.

Without trying a different OS I can't show that the westell isn't to blame, but I'm unhappy with a 5 second delay anyway..

cacroll
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cacroll

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said by justin:

What i mean is that a release/renew does not tell the wireless card to disconnect from the AP, then reconnect. There is only one AP during my release..renew commands, it has link all the time. It is just that between release and renew I have no IP and can't do anything except issue DHCP broadcast packets.

My home router is the westell that every other verizon user gets, millions sold. It might have an issue with its dhcp server but then every other person has the same issue, plus I see this delay at random hotspots using a variety of equipment. Not always 30 seconds. Sometimes 5 seconds, sometimes 30 or in between.

Without trying a different OS I can't show that the westell isn't to blame, but I'm unhappy with a 5 second delay anyway..


So how certain are you that you are truly connected to the AP, without doing the release - renew? Isn't it possible that the radio is busy re associating you to the Westell, as you wait for the release - renew process to complete?

I'd sure try powering the radio off and on a few times when I moved around, to see if that has any effect, without doing a release - renew.

Plus with your Westell, you can hopefully see the DHCP and AP activity log? Have you examined them, to see if they show anything interesting?

justin
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justin

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You would think it does, but I just went through the menus and cannot find any DHCP server logs

It is a westell wirespeed
Software Version VER:4.03.02.04
Software Model 4 Port Gateway
Description WireSpeed Data Gateway

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I think that it is fundamentally a DHCP process issue. It may be aggravated by coming out of a suspend state and or a wireless re-associate.

As stated connecting to a network via cable and executing an ipconfig /release then ipconfig /renew, you will still see the long time to reestablish the address. I see the same behavior with my Linux client. The delay happens whether I am using a SOHO class router (WRT54G – solid as can be device – only reboots when power or RoadRunner fails), a commercial class AP (Cisco 1200) connected to a Netgear firewall/DHCP server or Windows 2000 server managing DHCP.

Again, coming out of suspend your system will check to see if its information is still valid and renew its lease. That takes time. What makes you think it should only take 1 second? As for which SSID to connect to, when it finds two identical ones it will switch back and forth until it decides which one is best. That is why when a roaming system is set up it uses the same SSID and non overlapping channels. It allows the APs to hand off the client from one to the other without connection loss.

Hotspot A’s linksys and Hotspot B’s linksys obviously know nothing about each other, nor does your laptop know which is best so it goes through a constant search for the best.

As I recall, you can set your WZC client not to automatically connect to a default SSID. This may reduce your initial seek time. Until then I think we will all be waiting to get the ip address. Personally, in the scheme of my life, I take the 30 seconds to enjoy the aroma of fresh coffee and relax.
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A correction is order. My Linux clients run as virtual instances on a Windows laptop. Their virtual nics pass through the Windows system so my statement concerning them should be disregarded.

justin
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Why would it bother to renew its lease when it can't find the AP anymore, and there is a new AP noted for auto-connect available, & with a strong signal?

The first step when waking up is to note that the AP that was around is gone. At that point, it should forget all about leases it had, as they were assigned by the DHCP server with an IP that matches the old AP. Since most leases are for a day, it shouldn't even TRY to renew its lease, it should note the new AP has replaced the old one, and start from scratch and as fast as possible.

As for why a renew release should take 5 seconds, let me rephrase the question: 5 seconds is a huge amount of compute time, yet my cpu is idle during this time. The packets requesting a new IP don't walk slowly over to the AP and back again. So what is the breakdown of this 5 seconds? of course there must be stupid time-outs built in "somewhere" that could be eliminated entirely.
TheWiseGuy
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said by justin:

I get mad every time I watch it "acquiring an IP address" I want to shout at it: WHAT the HELL are YOU DOING RIGHT NOW that takes SO MANY CYCLES?
I got a long wait on one wireless machine on my LAN the other day, for "acquiring an IP address", and the computer had a static IP.