1242 AP over WAN Link

Unanswered Question
Nov 27th, 2007
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Hello,


We have multiple 1242 AP's (LWAPP) communicating with a controller back at the main site over a T1 (1.5Mb) connection. When bandwidth utilization is very high (close to 100%), wireless clients seem to lose connectivity for a short time. Netflow output shows the access points talking back to the controller using UDP 12222 (Ether tunnel?). Are the UDP packets being dropped... which is affecting wireless clients? Do I need to implement QoS to protect the UDP traffic on the WAN link?


Thanks.

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Richard Atkin Tue, 11/27/2007 - 09:19
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"Yes" is the answer.


Implement QoS for the LWAPP Control traffic and you should see a marked improvement.


It doesn't matter if client traffic sees the odd drop because it's normally just a UDP (LWAPP) wrapper around a TCP (Client Traffic) core. If the UDP LWAPP is dropped, the clients TCP stack realises there was no response and re-transmits as per normal TCP rules.


HTH,

Richard.

sometechguy Tue, 11/27/2007 - 10:10
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Ok, thanks. I'll post in a different area regarding QoS recommendations for LWAPP control traffic.


What is strange though is that all wireless clients on the access point temporarily lose connectivity for a time... then communication back to the remote site resumes. Wired clients do not experience a loss of connection, only slowness (delay).

Richard Atkin Tue, 11/27/2007 - 15:43
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The LWAPP Control traffic is UDP so likely to get dropped and not re-transmitted. LWAPP Control traffic is also very important because it includes all of the authentication, association & roaming (etc) information about the clients on the AP. When this information starts to go missing, all sorts of problems will occur.


Do you know if the AP manages to keep its association with the WLC? Or is it purely clients that are affected?


These documents should help you get a better understanding of how LWAPP works and how to implement QoS for such a setup.


http://www.cisco.com/en/US/tech/tk722/tk809/technologies_configuration_example09186a00807e9717.shtml


http://www.cisco.com/application/pdf/en/us/guest/netsol/ns279/c649/ccmigration_09186a00808d9330.pdf (big file, over 10MB)

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