Arch Linux

silverhammermba

Wiki Maintainer

Registered: 2011-04-14

Posts: 156

Frequent DHCP Failures with Wireless

I have a Thinkpad X1 Carbon, connecting to wireless using Wicd. On certain networks (especially unsecured ones, it seems) I get very frequent DHCP failures. In such cases I usually have to manually reconnect five or six times after Wicd times out in order to connect. I have confirmed that DHCP is the issue since the debug output prints

KeyError: dbus.String(u'dhcp_failed')

As suggested by the wiki, I have tried using dhclient instead of dhcpcd but that didn't seem to make a difference.

Exarch

Member

Registered: 2013-05-07

Posts: 5

Re: Frequent DHCP Failures with Wireless

Hi,
I just fixed a very similar issue. Did you just update dhcpcd? If so, a downgrade did the trick for me.

WonderWoofy

Member

From: Los Gatos, CA

Registered: 2012-05-19

Posts: 8,414

Re: Frequent DHCP Failures with Wireless

You have the X1 carbon?  What is the wireless card in that? I seem to remember that it used to come with the Thinkpad b/g/n card... though I could be wrong.  Maybe it was the Thinkpad a/b/g/n...

In any case, can you post the output of lspci -vnn?

silverhammermba

Wiki Maintainer

Registered: 2011-04-14

Posts: 156

Re: Frequent DHCP Failures with Wireless

Exarch, I've had this problem for a while. Like I said it seems to only happen on certain networks so I've just put up with it until now.

According to Lenovo, my wifi card is an Intel® Centrino® Advanced-N 6205S 2x2AGN. According to lspci

03:00.0 Network controller [0280]: Intel Corporation Centrino Advanced-N 6205 [Taylor Peak] [8086:0085] (rev 96)
        Subsystem: Intel Corporation Device [8086:c220]
        Flags: bus master, fast devsel, latency 0, IRQ 44
        Memory at f0c00000 (64-bit, non-prefetchable) [size=8K]
        Capabilities: [c8] Power Management version 3
        Capabilities: [d0] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [e0] Express Endpoint, MSI 00
        Capabilities: [100] Advanced Error Reporting
        Capabilities: [140] Device Serial Number 8c-70-5a-ff-ff-81-2d-74
        Kernel driver in use: iwlwifi
        Kernel modules: iwlwifi

Last edited by silverhammermba (2013-08-03 02:16:14)

silverhammermba

Wiki Maintainer

Registered: 2011-04-14

Posts: 156

Re: Frequent DHCP Failures with Wireless

Further investigation indicates that the DHCP client is not to blame. I seem to have trouble connecting to specific access points (that all share an ESSID), but if I find an access point that works then both dhcpcd and dhclient connect to it equally quickly.

WonderWoofy

Member

From: Los Gatos, CA

Registered: 2012-05-19

Posts: 8,414

Re: Frequent DHCP Failures with Wireless

This might be ongoing issues with iwlwifi.  There have been many fixes to the iwlwifi module in coming kernel version though.  So hopefully things will get better.  I had a coupel card that used iwlwifi and fortunately I never experienced these, but you are not the first person that I have heard of who has trouble connecting to certain networks.  In the past I have been told it is ceratin open public networks, but I am not sure if it is the same for you or not.

BGK

Member

From: France

Registered: 2013-07-06

Posts: 30

Re: Frequent DHCP Failures with Wireless

Those working AP... do they happen to be non N capable? (b/g only?)
If yes, try to deactivate the "N" capability on your computer:

Unload iwlwifi module
Add

options iwlwifi 11n_disable=1

to /etc/modprobe.d/iwlwifi.conf
Load iwlwifi module
See what happens

silverhammermba

Wiki Maintainer

Registered: 2011-04-14

Posts: 156

Re: Frequent DHCP Failures with Wireless

In the past I have been told it is ceratin open public networks, but I am not sure if it is the same for you or not.

That definitely seems to be the case. Public, unsecured networks tend to have the most problems for me.

I'll try to find out if there is some distinguishing features of the working APs but I'll need to track down who owns them first.

MariusMatutiae

Member

Registered: 2012-11-08

Posts: 31

Re: Frequent DHCP Failures with Wireless

Some time ago I posted this bug report:

https://bbs.archlinux.org/viewtopic.php?id=163489

That bug is still around. Is it at all similar to yours?

silverhammermba

Wiki Maintainer

Registered: 2011-04-14

Posts: 156

Re: Frequent DHCP Failures with Wireless

I don't think I have the same bug - no infinite loop or anything like that. DHCP fails (I think it times out) and that's it.

I spoke to the sysadmins about it and aside from seeming a little clueless, they expressed concern that Wicd could distinguish between access points for the network. They said it was a "mesh" network (or something) and most of the APs were just repeaters. I've tried using Wicd's "use these settings for all networks sharing this essid" option so that it would hopefully act less discriminatory about which AP it's using but that didn't seem to help. It would just fail over and over again to connect until it happened to find the AP that works.