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1 side can't hear Calls from Cisco 3905 phones

Medium Priority
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Last Modified: 2020-06-18
We recently started noticing that a certain floor of a building on campus can only call 1 direction.  When either side tries to call the one side in the bottom of our building cannot hear anything that the other side is saying. This only happens to the 3905's on the first floor of a specific building. If you use a higher model phone on that floor it doesnt happen and if you bring a 3905 up a floor or anywhere else and it functions perfectly.  Strangely, this isn't consistent as some 3905 phones on that floor can call some phones in other areas of the building and there are no problems at all.  I am stumped.  Any suggestions would be appreciated!

Phone system is Cisco
Switches are Cisco 2960S-48fps-L models with IOS 15
Call Manager and Unity versions are 11.5.1
Phone affected on the first floor of the one building are Cisco 3905's

If any log files are needed I can provide those.
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Commented:
routing issue more than likely.

Start with some ping/traceroutes from both ends.  If the calls are internal then from the same subnets as the phone, if they are external too also to the gateways and from the gateways.
Josh RogalskiNetwork Technician

Author

Commented:
The phones can call some people on the same subnet and you get 2 way calling.  They can call people are our far site routed on a totally different subnet and different physical site and there are no issues.   The real oddity has been that there is almost no rationale why this started happening last week.  I can't think of anything that would have precipitated it.

Additionally, why does it only happen to Cisco 3905 units on that floor?  We swapped it out with a nicer Cisco phone on the same network port and all calls work perfectly.
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Commented:
Does the replacement phone get an IP on the same subnet?
Josh RogalskiNetwork Technician

Author

Commented:
Yes, both phone devices get IP addresses in the same subnet.  Additionally, when you call from the bottom floor with the 3905 it has the 1 way calling issue, but disconnect it, bring it to another switch on a different floor and it functions correctly.  I reviewed the switch but don't see anything that could be causing the problem.
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Commented:
layer 3 switch?  have you run a traceroute to the far end device and from the far end device to the local device?
Josh RogalskiNetwork Technician

Author

Commented:
Layer 2 switch up to our core.  But all the phone traffic is on the same vlan so it doesn't even route to the other phone. I ran the tracert command from my desktop machine to the phone in question and it completes as I expected it to.   There are about 12 phones that all do this off the same switch but again, it doesn't happen consistently.
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Commented:
well this is very odd, have you opened a case with Cisco TACC?
Josh RogalskiNetwork Technician

Author

Commented:
Yes a case has been opened with TAC, since I am not the phone system admin I am not privy to the communication.  I will check in with him today and see what the status is.
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Commented:
Ok, kind of confused on this one too, so let me know.  Typically my goto for one sided audio is routing.  But that sounds solid.  If they are on the same VLAN and no routing in between, then I might think firmware so something too.
Josh RogalskiNetwork Technician

Author

Commented:
We are planning to apply an update to Call Manager and Unity to bring us up to version 12.5 (currently on version 11.5).  I am told (but haven't verified) that the update of the software also updates the firmware repository and then the phones auto install the latest firmware build.  This isn't happening until our large maintenance window in 2 weeks.  I will reply back once that happens as I am suspecting it will fix this issue and bunch more.  

In the meantime, can anyone confirm or deny my statement about the firmware repository update?  I had heard that new versions bring along the newest firmware but wasn't sure.
Josh RogalskiNetwork Technician

Author

Commented:
The plot both thickens and thins at the same time.  On a hunch, I disconnected a second smaller switch that is connected to the switch in the network closet that the phones are connected to.  Once I disconnected that switch, the 3905 phones started working again perfectly and an AP that was malfunctioning came back without issue.  Did some test calls, then reconnected the small Cisco WS-C2960CX-8TC-L switch and the 3905 phones started malfunctioning the same exact way again.  Any thoughts on this bizarre news?
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Commented:
Were the phones connected to that switch?  That is odd behavior unless STP or other layer 3 issues are being created by its presence
Josh RogalskiNetwork Technician

Author

Commented:
The phones are connected to the 2960S 48 port switch.  The small 8 port switch I unplugged is plugged into the 2960S 48 port.  All the items malfunctioning are on the 48 port, but are all fixed by disconnecting the 8 port.  Very odd. Adding in more tags to broaden the scope of this.
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Commented:
can you post the config of each switch?
Josh RogalskiNetwork Technician

Author

Commented:
I have attached both configs, the small 8 port switch and the 48 port switch.  I removed anything that was confidential.  Everything in here is now just generic switch settings.  I am interested to see if there is something I configured oddly that might need to be changed.  I should note this config is how we have all the switches set and have had no issues of this kind.
2960CX_8config.text
2960S_48config.text
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Commented:
so at a quick review, and I may be wrong so correct me, the 8 port connects to port 48, port 48 is a access port with a voice vlan, but on the 8 port i dont see voice vlan and it may be a trunk port.
Josh RogalskiNetwork Technician

Author

Commented:
The 8 port switch is connected to port 40 on the 48 port switch.  I just added the voice vlan to the small 8 port switch, but didn't think it needed it since no phones will plug into the small 8 port switch.  If you create a trunk port do you need it to have more than 1 vlan on it?
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Commented:
ok, I missed that, I thought the malfunctioning devices were on the 8 port.

As for the trunk you can trunk all vlans or specific. using switchport trunk allowed vlan add ...

I just cant see why that would work, try running show spanning-tree on the 48 port
Josh RogalskiNetwork Technician

Author

Commented:
Attached is the output of "show spanning-tree" on the 48 port.  Not a ton of this makes sense to me but the variations seem to be the two trunk ports, which I would expect.
spanning-tree-output.txt
Hi Josh
What is connected to port 52? It’s a trunk port.
Network Technician
Commented:
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