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Cisco Routers/Switches and Avaya VoIP phones

I recently inherited a small Cisco network that is using Avaya VoIP phones. Since the previous administrator knew nothing about networks, everything was configured in 1 large VLAN. Now, I am trying to move the phones over to a 172.16.128.x/24 VLAN to seperate voice traffic from data traffic. the general switch (a Cisco 3750) port configuration is this:

interface FastEthernetx/x/x

switchport access vlan 128

switchport trunk encapsulation dot1q

switchport trunk native vlan 128

switchport mode trunk

switchport voice vlan 130

load-interval 30

mls qos trust cos

no cdp enable

spanning-tree portfast

spanning-tree bpdufilter enable

Once you configure the port with the above settings and reset the phone, the phone does come up on it's new IP settings (on the 172.16.130.x/24 subnet) and works fine, as does the PC. But before you reset the phone if you add the above port configuration and just reboot the phone (not do a reset), the phone comes back on it's older 172.17.x.x/22 IP settings and works just fine. Routing between VLAN's is done off of the 3750 on a subinterface configured on a 3745.

So my question is, since the phone seems to be pulling from DHCP and "then" pulling an IP address from the Avaya server (on the 172.17.x.x/22 subnet), why would it work on a subnet (172.16.130.x/24) for which it does not have an IP?

I'm no Avaya or VoIP expert (but i'm working on it), so I wanted to see if someone with more experience might know. Thanks.

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