DHCP for IP phones and computers

jskfan used Ask the Experts™
in the topology below I have Cisco IP phone connected to Cisco Switch and a computer connected to IP Phone. I have seen this scenario in the environment I worked in.

Well, let 's say IP phone needs to be in Vlan 10 and the computer needs to be in Vlan 20.
How do you configure the Switch to be able to hand out IP addresses for IP phone and computer?

Assuming Windows DHCP server is connected somewhere in the Network (to a different switch than the one shown in the topology)

Any illustration will be very much appreciated.

Thank you.
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Distinguished Expert 2018
Usual way at Cisco switch you configure port as access port (but there are few ways), and then you configure the same port as part of voice VLAN.

(config)# interface fa 0/1
(config-if)# switchport mode access
(config-if)# switchport access vlan 20
(config-if)# switchport voice vlan 10

You need to configure ip-helper on VLAN interface for addresses for DHCP server, configure QoS, set trust boundary for QoS etc...
DHCP server need to be configured with address of TFTP server (in Cisco case  option 150 - for Microsoft I think it is option 66)

For cable connection you have just one cable from switch to phone (usually marked as 10/100 SW ) and other cable from phone to PC (10/100 PC).
If PoE is present on switch, you need to enable it under interface, command is:
power inline {auto [max max-wattage] | never | static [max max-wattage]}
If PoE is not present - you need power adapter, or PoE injector.


Thank you !

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