De or het routering?

The correct Dutch article is:

de routering

Rule Words ending in -ing: almost always de. See the rule

How to use routering

the routeringde routering
this routeringdeze routering
that routeringdie routering
our routeringonze routering
your routeringjouw routering
every routeringelke routering
which routering?welke routering?
a big routering / the big routeringeen grote routering, de grote routering