The control link relies on a proprietary protocol to transmit session state, configuration, and liveliness signals across the nodes. On a services router, the control link is a physical link connecting the control interfaces on the two nodes of the cluster (the pair ge-0/0/0 and ge-0/0/3.
To set up the control link on services routers, you connect the control interfaces on the two devices back-to-back. When you initialize a services router in cluster mode, JUNOS software with enhanced services renames the control interface to fxp1 and uses that interface for the cluster control link. To enable the control link to transmit data, the system provides each fxp1 control link interface with an internal IP address.
On a services gateway, by default, all control ports are disabled. Each SPC in a device has two control ports, and each device can have multiple SPCs plugged into it. To set up the control link on a services gateways, you connect and configure the control ports that you will use on each gateway (fpcn and fpcn) and then initialize the services gateway in cluster mode.
