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Added a VLAN to the trunk....shut down half our phones.


So, we were testing some things in the IT lab today, things we didn't think would do any harm on a live production environment. Well, we were wrong. lol We have it back up now, but I can't stop wondering WHY adding a VLAN (the subnet our CME is in) to the trunk would just shut down everything on that switch stack (at least the 1st switch of it). I replaced some numbers with 'x's for security reasons, but here's the VLAN config: 

interface Vlan248
description Cisco VOIP
ip address
no ip redirects
no ip proxy-arp
standby 0 preempt delay reload 500
standby xxx ip
standby xxx priority 110
standby xxx preempt
standby xxx authentication md5 key-string 7 #######


Why would adding this to the trunk bring stuff down. (Side note, this VLAN was still allowed on the trunk when it was no longer configured on any switchport. Maybe that's a reason?)

5 Replies 5

about the op150 , is it solve ?

for this draw topology 

we're still working on it

Georg Pauwen
VIP Master VIP Master
VIP Master


tough one. How exactly did you add the Vlan to the trunk, did you use the 'vlan allowed' command ? Do you remember the exact command sequence you used ? I guess if you did use the 'vlan allowed' command, as soon as you enter that command on one interface, there will be a mismatch on the other side, which could have caused your issues...

I actually just added the VLAN to the allowed list. And yepp, I bet you're right. Pretty obvious, and yet I didn't think of that. 

A mismatch is an interesting possibility. I also wonder about the possibility that when you added the vlan to the trunk it connected the vlan to other devices and perhaps created a loop and spanning tree took down your phones?


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