Yealink SIP-T2 Series Auto Provisioning Manual page 69

Set the custom DHCP option (custom DHCP option tag number ranges from 128 to 254)
7.
and select the option type (Yealink supports string and ipaddress option types only). Click
the OK button to finish setting the option properties. Click
Click Named Policies-->Global, right click the blank area on the right of the main page
8.
and then select New Option.
Appendix
to save the change.
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