Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
I'm assuming in a configuration where the Avaya phone connects to a network switch, and the PC connects to the Avaya phone, correct?
Normally, the PC is just passed through the Avaya phone and runs on the network switch, natively, i.e. no VLAN tagging.
The Avaya phone can also run with no VLAN tagging, as just another host off the network switch's port. However (commonly?) the Avaya phone will run in a different VLAN and used tagged frames to/from the switch.
I believe the Avaya phone might be hardcoded to start with VLAN tagged frames, but what we do, is have the Avaya phone pull a DHCP IP from the native VLAN. Within the DHCP options, there's an option to inform the Avaya phone to change to a different VLAN. When it does, it then uses tagged frames and pulls a new DHCP IP on that VLAN. (On Cisco devices, port is typically configured as an access port with a voice VLAN too.)
To more specifically answer your questions, I believe the PC generally runs such that it doesn't realize there's an Avaya phone in its physical path. The Avaya phone, might boot itself in couple of different ways, one being, as described above, it uses DHCP options during its startup process.
As far as I know Avaya phones don't support CDP (but they do often support LLDP).
First packet from the Avaya might start, I believe, with untagged or tagged frames; it depends on how the Avaya phone has been configured.
DHCP discovery is "normal", if hosts (both Avaya and PC) are configured for it.
