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When a device is plugged into a switch (let's say, a Cisco Catalyst switch) how does a switch know whether the device is a VoIP one - and subject to being placed into the voice VLAN - or some other kind, i.e., a data device, and this subject to being placed into the data VLAN?

I know the question may sound dumb but this is the best way I can ask it.

Thanks.

Boris.

Boris Epstein
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1 Answers1

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Generally it is either 1 of 2 ways: Either the phone is getting it's configuration information (including VLAN information) from some source (DHCP option/config download/etc) or the switch is using LLDP (Link Layer Discovery Protocol) to discover it's a phone because the phone is advertising with LLDP that it is a phone.

Rex
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