Network control system for configuring middleboxes

A non-transitory machine readable medium storing a program for performing middlebox operations on a host computer executing a middlebox element having a plurality of middlebox instances and a plurality of end machines, the program comprising sets of instructions for:

• receiving a data packet from a managed forwarding element via a software port between the managed forwarding element and the middlebox element having the plurality of middlebox instances, wherein the managed forwarding element executes on the host computer to implement a plurality of logical networks;
• based on a tag that the managed forwarding element associated with the data packet, selecting from the plurality of middlebox instances a particular middlebox instance associated with the tag;
• using the selected middlebox instance to perform a middlebox operation on the received packet;
• and
• sending the processed data packet to the managed forwarding element.