[cisco-voip] Cisco 8851 and MSTP

[Michael David]

Just a heads up to anyone running 8800-series phones and using MSTP. 

We're in deployment of a new 10.5 CUCM system with 8851 and 7841 phones.  A few times now we've been hit with network loops as janitors empty rooms to clean/wax and then replace stuff, plugging in everything they see loose. The loops have only been happening with 8851 phones.  With the 7841 phones, bpduguard shuts down the phone almost as soon as connected. With the 8851s, the loop runs unchecked.. and affects the entire site, almost like the phone is filtering BPDUs. However, I took a phone and switch into the lab, and after a little testing have found that the problem only occurs when using MSTP.

Switch: WS-C2960XR-48FPD-I
Switch firmware: 10.0(2)EX5
Phone firmware: 10.2(2)
Test case log: http://pastebin.com/gm5emaZa

I can't currently test this with the 10.3 firmware, but I saw no mention of spanning tree in the 10.3 release notes. In the short term, I'll probably have to switch all of our switches to rapid-pvst. Convergence with non-cisco equipment will be slower, but that's the lesser evil here. Hope I've saved someone else some grief. :-)

Michael

--
Michael A. David, CCNA 
Springfield Public Schools
Technology Service Center
217.585.5802 ext. 85114
217.585.5809 (FAX)