There are hundreds of hiking trails in Tehran, and Darabad trail is one of the 5 most popular ones. What distinguishes this trail from the other 4 is the fact that there is only one restaurant there, so the trail is very clean and not that crowded.
On the foot of Mt. Darabad there used to be a village called Darabad which is currently a part of Tehran metropolitan area. The northern slopes of Mt. Darabad extends down to the villages of Ooshan and Hajiabad. They were planning to build a huge recreational center including ski resorts in Hajiabad and northern slopes of Darabad, but apparently the plan is on hold.
To get to the summit of Darabad, you can go from any direction you want. You can start your hike from the village of Hajiabad in the north or from Darabad region in Tehran or from Piazchal on the west.