[cisco-voip] phones working on a dumb switch with voice/data vlans switched properly

[Dave Goodwin]

I haven't really tried the kind of thing you described in quite a long
time. But I assume the reason the phone gets an IP address is because the
CDP VVLAN information is being successfully sent through the unmanaged
non-Cisco switch so the phone actually sees it. The phone learns its VVLAN
ID, so starts tagging all its frames and therefore gets an IP from the
VVLAN. The other devices plugged into the switch (or behind the phone)
don't normally need to tag, so the frames are coming through up to the
Cisco switch untagged and are therefore in the native/access VLAN on the
port and getting one of those IPs.

So I guess that unmanaged switch passes any CDP through to all ports, and
also passes any tagged traffic through unaltered.

On Wed, Oct 3, 2018 at 5:17 PM Lelio Fulgenzi <lelio at uoguelph.ca> wrote:

>
> OK - I'm probably showing my ignorance here, but I was quite surprised to
> find out that plugging in a dumb Dlink DES-105 switch into our cisco switch
> with access layer programming, so data vlan and voice vlan, extended things
> such that when a phone is plugged in, it got an IP address on the voice
> vlan, and plugging a non-phone device got an ip address on the data vlan
> and then plugging a similar device into the back of the phone also got an
> ip address on the data vlan. We plugged in multiple phones as well. All
> worked fine. *phones powered by brick*
>
> I can appreciate a passthrough device, I've used them before as ethernet
> extenders. By what I'm not understanding is how traffic is being classed
> properly through to this dumb switch.
>
> We're using a new 9300 series switch, but I'm not sure that would make a
> difference.
>
>
>
> ---
> Lelio Fulgenzi, B.A. | Senior Analyst
> Computing and Communications Services | University of Guelph
> Room 037 Animal Science & Nutrition Bldg | 50 Stone Rd E | Guelph, ON |
> N1G 2W1
> 519-824-4120 Ext. 56354 | lelio at uoguelph.ca<mailto:lelio at uoguelph.ca>
>
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>
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