WLAN: Windows7 client and L3 roaming problems with DHCP

[mlopacinski]

Hello

I have one SSID with many AP's, AP's on each floor connects to another L3 IP subnet.

When windows7 client roams between floors he associates with new AP, send DHCPRequest with old IP address, receives NACK from DHCP server and does not try to send DHCPDiscovery to receive new IP address.

WindowsXP client does not have this problem, also linux/android/apple does not have this problem. Only Windows7 professional and ultimate.

1. Does anybody noticed similar problem ?

2. Does cisco WLC has any options to loadbalance clients which are already associated ? To deassociate them ?

I guess that modern WLAN controlers/AP should notice that client is associated to AP with 30% signal and could be associated with another AP with 90% signal - in such case AP should send deassoc to the client forcing him to associate to better AP.

Thanx

[Scott Fella · Accepted solution]

As long as you have connectivity when roaming between floors, devices would keep their ip address (seamless roaming). If they drop their connection (poor coverage/shut off device/etc) they will obtain an ip address depending on what ap they connect to and how you have your wireless configured.

There is a feature in the wlc WLAN SSID advanced tab (lower right of the page) called client load balancing. This will try to load balance users, but it is still up to the device to what ap the device wants to associate to. This feature you must test out. Apple devices and some HP and Dell seem to have issues with this when you have around 10-15 devices on a given AP.

Hope this helps

Sent from my iPhone

[dfeddersen]

We have been having the same L3 roaming issue ever since we went to Windows 7.  For whatever reason, Windows 7 won't try and pull a new IP address when roaming to an AP in a different subnet.  Any ideas?

I ran into this article about configuring the DHCP Hint feature on Windows 7, but that did not appear to help either:

http://blogs.technet.com/b/teamdhcp/archive/2008/12/19/how-to-configure-dhcp-network-hint.aspx

http://blogs.technet.com/b/teamdhcp/archive/2008/12/19/what-is-dhcp-network-hint.aspx

[Scott Fella]

How is your wireless setup and what

Is the purpose of having devices renew dhcp every time the device roams to an AP that is on a different subnet? Most of everyone want seamless roaming and that is what the WLC provides.

Sent from Cisco Technical Support iPhone App

[dfeddersen]

Typically there are different subnets for different floors, and they aren't going to seamlessly roam when in an elevator or stairwell anyway.  I just need them to get a valid IP address when they take their laptop to a conference room.

[Scott Fella]

So how do you have your wireless setup, AP groups to map floor ap's to a vlan?

When you move from one floor to another, do you drop your wireless connection?

Sent from my iPhone

[dfeddersen]

Yes, wifi can drop when moving between floors. This isn't an issue for us, but not pulling a proper IP is.

Just to note, this isn't a Cisco specific issue.  I have seen this with other vendors as well.  It is a Windows 7 issue, and was curious if anyone found a fix.  XP and Vista work fine.

[Scott Fella]

Interesting. I never ran into that yet, but maybe that would be a good test.

Sent from my iPhone

[mlopacinski]

@dfeddersen: i have EXACTLY the same problem. Other OS and windowsXP works fine. The problem is only with windows7, which does not refresh ip address. I've tried to disable network hint in registry but this did not help. I do not have cisco WLC solution (use ruckus wireless) - so i can not solve this problem with seamless L3 roaming (besides - i do not want to send traffic tru controller).

[mlopacinski]

I found the source of the problem: and it's....cisco vpn client...

When installed on windows7 it replaces some libs and breaks WLAN roaming !

It does not matter if it's windows 7 64bit or 32 bit, or language version, or service pack1 or not - for all versions cisco vpn client breaks WLAN roaming - and the effect is that windows do not send DHCP request after roaming to another AP within the same SSID.

I wonder if anyconnect has similar bug...

[dfeddersen]

You're right!  That was it.  I uninstalled the Cisco VPN client and it works fine on my PC now. 

I have AnyConnect 2.5.3055 and it appears to work fine without any issues.

Thank you!

[mlopacinski]

Found the problem inside cisco vpn client. It's a bug in DNE component written by citrix.

http://www.citrix.com/lang/English/lp/lp_1680845.asp

If you want to use cisco vpn client and have working roaming install:

ftp://files.citrix.com/dneupdate.msi for 32-bit system

ftp://files.citrix.com/dneupdate64.msi for 64-bit system

Tested with 64bit and it solves problem. I will report problem/solution to cisco so they could ship vpn client with updated DNE.

[dfeddersen]

Just out of curiosity, how did you narrow it down to the Cisco VPN client, and then narrow it down to that specific Citrix component?

Thanks!

[mlopacinski]

to narrow to Cisco VPN Client i needed a lot of time, about 5 different laptops and microsoft specialist from our company which accidently did not use VPN Client and had correctly working system.

to narrow to DNE: i already new that installing vpn client makes problems so: on fresh windows7 installation i've counted md5 sum for all files (using fciv), then installed cisco vpn client and counted md5 again. Found about 100 new/edited files. All of them were typical/obvious except DNE...