Yealink T58A Manual page 59

You can add a custom option via DHCP Turbo. Select Option Types, right click one of the
6.
options on the right of the main page, and then select New Option Type.
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
Appendix
to save the change.
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