I have a quick question regarding the correct use of ip helper-addresses. I have a typical setup: voice and data on separate vlans, with a Windows DHCP server giving out addresses for both.
Data Vlan: 1
Voice vlan: 100
DHCP Server: 172.16.99.1
Data DHCP Scope: 172.16.96.XXX
Voice DHCP Scope: 10.16.96.XXX
I have one site whose phones will not get a DHCP lease, unless I disable the data DHCP scope on the server - which suggests to me that the ip helper-address is not configured correctly. As soon as I disable the 172 scope, the phones grab an IP.
On the router, the helper address is currently set on the voice vlan subinterface:
encapsulation dot1q 100
ip dhcp relay information trusted
ip address 10.16.96.1 255.255.255.0
ip helper-address 172.16.99.1
The switchports are configured as such:
switchport mode access
switchport voice vlan 100
mls qos trust device cisco-phone
mls qos trust cos
auto qos voip cisco-phone
Is this the correct way to do this? If not, where exactly should the helper address be configured? Is there something else I am missing?