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Beginner

Voice and Data (2 seperate vlans) from an access port, through a downstream unmanaged switch.. to a working pc/phone?

Topology is a provider network with some managed switches where voice and data are separate; only 2 vlans total 1 for voice and 1 for data. Would like to connect an unmanaged switch to this environment to an access port on the managed switch with both the voice and data vlan associated with it.  
 
If I hook up an unmanaged switch (cisco branded, good quality, 110 series) in this fashion, further across campus, will pc's and phones work attached to the unmanaged switch?
 
ManagedSwitchAccessPort(DataVlan1/ViopVlan2)>ethernet>UnmanagedSwitch>ethernet>phones/PC's
 
I've poked around and there was some debate with some claiming some manufacturers work and some don't. There was conflict on whether or not the vlan data would get stripped and readded (it's not a trunk so...). Your feedback please; the client wants to keep cost down (it's only 3 phones.. and some PC's on a small project) but the supply chain can take months. So would like to know in advance before 3 months of anticipation turns into a cost saving dud. Prefer answers from direct experience if you have it, or absolute confidence if you have that; I've already seen enough guesstimating. Thanks.

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Rising star

Re: Voice and Data (2 seperate vlans) from an access port, through a downstream unmanaged switch.. to a working pc/phone?

vlan data will not get stripped and re-added! (after all the unmanaged switch knows nothing about vlan's!)

it will just look at the header in particular destination MAC address and will forward the packet unchanged.

even CDP packets that normally stop at the receiving Cisco switchport will be forwarded unchanged,

(you should even be able to pass a switch trunk through an unmanaged switch)

so even Voice vlan discovery through CDP will work.

 

[added] be aware of maximum frame size the unmanaged switch can handle.

Because of the vlan information in the packet the max size is a little smaller

 

look at the last posts in this thread

3 REPLIES 3
Rising star

Re: Voice and Data (2 seperate vlans) from an access port, through a downstream unmanaged switch.. to a working pc/phone?

vlan data will not get stripped and re-added! (after all the unmanaged switch knows nothing about vlan's!)

it will just look at the header in particular destination MAC address and will forward the packet unchanged.

even CDP packets that normally stop at the receiving Cisco switchport will be forwarded unchanged,

(you should even be able to pass a switch trunk through an unmanaged switch)

so even Voice vlan discovery through CDP will work.

 

[added] be aware of maximum frame size the unmanaged switch can handle.

Because of the vlan information in the packet the max size is a little smaller

 

look at the last posts in this thread

Beginner

Re: Voice and Data (2 seperate vlans) from an access port, through a downstream unmanaged switch.. to a working pc/phone?

 Awesome thanks this is how I thought it would work too, I just never saw the question spelled out quite the way I wrote it and the answers  I did see were ambiguous or conflicting to my specific situation.

 

As for the cdp traffic, I did see this in another similar condition; not over a switch but in point to multipoint wireless bridging, which in around about way is performing the same role as a switch but over a different medium with different tech.

 

 Thanks for the in-depth response.

 

 

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VIP Expert

Re: Voice and Data (2 seperate vlans) from an access port, through a downstream unmanaged switch.. to a working pc/phone?

It will work, but if you place both VLANs on the unmanaged switch, effectively you've bridged the two VLANs. What would be better is to use two unmanaged switches, one you connect to the data VLAN and the other to the voice VLAN. (BTW, the VoIP phones on the unmanaged switch would need to be configured to not use VLAN tags.)
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