In the following circuit, the equivalent resistance between A and B is

From circuit diode $A$ and diode $B$ both are in reverse biased 

so equivalent circuit is

All resistance are in series combination 

so $R_{eq}=R_1+R_2+R_3$

$\Rightarrow R_{\mathrm{eq}}=8+2+6=16 \mathrm{\Omega }$