Voice VLAN not working on Cisco C3850

[WhyFi]

We replaced some switches in our environment with Cisco Model C3850.

On the other switches (C3560CG and multiple C3560E) the voice vlan was working without problem. 

We had a VLAN for voice and "switchport voice vlan <id>" on the interface. When we connect an Audiocodes IP Phone it, it would automatically choose the Voice VLAN. And with "show cdp neighbors" we were able to see the IP phones.

Now with the C3850 I use the same commands to activate the voice vlan, but when we connect a phone, it will still choose for the native vlan configured on that port.

More info about the C3850: Model: WS-C3850-48P, SW Version16.3.5b, SW Image: CAT3K_CAA-UNIVERSALK9

Are there additional commands needed to enable this? I tried "trust device cisco-phone", but it doesn't help.

I tried some commands explained here: https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_0100011.pdf

like "mls qos global", but the switch won't recognize that command. Do I maybe use a bad image on the switch?

[Mark Malone]

Hi
Because its non Cisco it doesnt get the voice vlan off CDP automatically but with the voice vlan id tag it should work

Does it work when configured as standalone with no data vlan in place on the port just the voice vlan set ?
maybe its not receiving the option correctly when it boots up from dhcp

what exactly is the port config on the 3650 for teh phone and data setup

qos wont help regarding this , something not being negotiated right when phone starts up

[WhyFi]

The phones work fine with CDP and our previous Cisco switches even detect them with "show cdp neig"

See screenshot: 

I will try LLDP, but I find it strange that I have to use it just for these new switches.

The port config is this:

interface GigabitEthernet0/1
 switchport access vlan 200
 switchport mode access
 switchport nonegotiate
 switchport voice vlan 215
 spanning-tree portfast
 spanning-tree guard root
end

If I place the interface in switchport access vlan 215, the phones receive an IP from vlan 215, so I know the vlan and DHCP are working. But with above config they only receive an IP from vlan 200.

[Mark Malone]

I would run a wireshark too and span the port as phone is booting up , see exactly whats going on at the wire level , that way you can see the DHCP offers requests and other info , base it against a working 3560 switch output could show the difference
I have 100s of these switches configured same way as yours and we don't have this issue , it may be software related too specific to the image , were running 16.3.7 and its very stable

[Georg Pauwen]

Hello,

in addition to Mark's suggestion, and since the Audiophones are non-Cisco devices, you might try LLDP instead of the default CDP on the ports the phones are connected to...

3850#configure terminal
3850(config)#lldp run
3850(config)#interface interface-id

3850(config-if)#lldp transmit
3850(config-if)#lldp receive

[WhyFi]

LLDP works without problem on the new switches. Thanks.

I still find it strange that CDP works on older switches and not on these newer switches.

I'm guessing Cisco must have blocked the usage of CDP for non-Cisco phones on their newer switches..

These are the options on the Audiocodes (And they literally work on all other Cisco switches we have):

[Georg Pauwen]

Hello,

is LLDP (Cisco uses LLDP-MED as far as I recall) enabled by default on the older switches ?

[WhyFi]

No. And that won't explain how they appear in "show cdp neighbour".

Also, the Audiocodes literally have a CDP and an LLDP option. 

[Mark Malone]

The CDP version is the same in IOS and IOS-XE , i just checked a 35 and a 36 both default cdpv2

wireshark will show you whats going on

[NetCat]

I have the similar issue with C3850 on IOS-XE 16.3.6

Cisco phone C6945 and C9845 do not pickup the Voice VLAN and keep using data VLAN for DHCP. Wireshark captured the conversion and it points to switch image (Some version, not all.)

We have a TAC case with Cisco and hope I could get something (Like a software BUG) out of it.

[emiliolara]

Enabling the LLDP on our 3850 Stack version 16.3.5b fixed the issue.