Refer to the exhibit. What is the missing parameter that is shown as a red question mark in the exibit?

R$1$# interface gigabitethernet $0/0/1\mathrm{.}20$

R$1$# Encapsulation dot$1$q

R$1$# Ip address $192\mathrm{.}168\mathrm{.}20\mathrm{.}254255\mathrm{.}255\mathrm{.}255\mathrm{.}0$