Defina o valor da opção 51 para 4294967295 segundos e ele aparecerá na GUI como ilimitado.
C:\Users\EAnderson>netsh dhcp server scope 10.0.0.0 show optionvalue
Changed the current scope context to 10.0.0.0 scope.
Options for Scope 10.0.0.0:
DHCP Standard Option : General Option Values: OptionId : 51 Option Value: Number of Option Elements = 1 Option Element Type = DWORD Option Element Value = 3600 Command completed successfully.
C:\Users\EAnderson>netsh dhcp server scope 10.0.0.0 set option value 51 DWORD 4294967295
Changed the current scope context to 10.10.10.0 scope.
Command completed successfully.
C:\Users\EAnderson>netsh dhcp server scope 10.0.0.0 show optionvalue
Changed the current scope context to 10.0.0.0 scope.
Options for Scope 10.0.0.0:
DHCP Standard Option : General Option Values: OptionId : 51 Option Value: Number of Option Elements = 1 Option Element Type = DWORD Option Element Value = -1
Command completed successfully.
Exercício para o leitor: Por que 4294967295 é especial?