Hi could someone help me.. my brain isnt working and im in need of some help..

im getting LGFL to setup a new range on our network as we will be putting the network into vlans.. they have given me a /21 range but has asked this question.... can someone help me with an answer im not sure what to tell them or what it would mean with setting up the vlans.. or its just monday morning back from xmas and im being thick...lol..

"if you can let me know what subnet you are planning to use for the link segment (this will need to come out of the /21 range) and once the routing is completed I will configure the new interface with that"