08-19-2019 09:39 AM
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.
Solved! Go to Solution.
08-20-2019 07:45 AM - edited 08-20-2019 07:51 AM
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
08-20-2019 07:45 AM - edited 08-20-2019 07:51 AM
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
08-20-2019 08:25 AM
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.
08-20-2019 08:51 AM
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