I have Polycom IP 450 phones on Netvanta 7100.
When they boot, the default mode is DHCP, they contact the TFTP server, correctly populate the FTP field, login, and password, and then hang for a long time, cannot find (or login to) boot server,
and keep endlessly booting, and rebooting.
I tried to access FTP server manually from the browser, but cannot do it either.
There was 1 time out of 20-30 attempts when a brand new IP 450 was able to load everything correctly, and register. Even in that case, when disconnected, and connected again ended up in endless boot.