The club allocations for steps 1 to 4 of the National League System have been confirmed for 2017/18 and are now available on the FA website. They are subject to a 14 day appeal so may change.

http://www.thefa.com/news/2017/may/12/national-league-system-steps-1-to-4-allocated-140517

In summary,

the following sides will be joining the Isthmian League Division 1 North
AFC Sudbury, Canvey Island and Grays Athletic (relegated from Isthmian Premier)
Barking (promoted from Essex Senior)
Mildenhall Town (promoted from Thurlo Nunn)
London Colney (promoted from South Midland League)
Potters Bar Town (transferred)

 

the following sides will be departing the Isthmian League Division 1 North
Brightlingsea Regent and Thurrock (promoted)
Wroxham and Great Wakering Rovers (relegated)
Phoenix Sports, Thamesmead Town and VCD Athletic (transferred)

 

Ware have been reprieved following Worcester City’s drop from step 2 to step 5.

Full list