Port Control Protocol (PCP)
Use this screen to view, add, or delete PCP rules. Port Control Protocol (PCP) allows devices such as web or file sharing servers behind the Zyxel Device to receive incoming traffic.
Example A pplications
Some remote access applications, such as remote desktop or SSH, require incoming traffic to be routed to the user's device in order to establish a remote connection. Use PCP to dynamically map incoming traffic to the user's device, allowing them to establish remote connections.
The PCP server allows dynamic mapping of external ports to internal IP addresses and ports. PCP allows devices to request and release mappings for specific ports, and to specify the lifetime of those mappings. This allows devices to dynamically open and close ports just as needed, and does not need keepalive packets that can drain battery life of home devices such as smartphones.
In the following figure, the Zyxel Device is the PCP client. DS-Lite tunnels IPv4 packets over an IPv6 network to an AFTR (Address Family Transition Router) and Carrier-Grade NAT (CGNAT) which includes the PCP server, then sends traffic to its external IPv4 network. The Port Control Protocol with DS Lite allows you to create PCP mapping rules with the PCP server.
Requirement
You must enable DS Lite (Dual-Stack Lite) in Network Setting > Broadband > Edit WAN Interface to use PCP.
If you select Automatically configured by DHCPC, then the IP address of the PCP server is in assigned to the Zyxel Device using DCHP Option 64.
If you select Manually Configured, then you must enter the IPv6 address of the PCP server in the DS-Lite Relay server IP field.
Configuring PCP
Click Network Setting > NAT > PCP to display the following screen.
Network Setting > NAT > PCP
The following table describes the fields in this screen.
Network Setting > NAT > PCP 
LABEL
DESCRIPTION
Add New Rule
Click this to add a new PCP rule.
#
This is the index number of the rule.
External IPv4 Address
This displays the external IP address assigned by the PCP server. PCP maps from this IP address to the LAN device IP address.
Required Internal Port
This displays the internal port number that the PCP server maps to, from the external port.
Required External Port
This displays the proposed external port number that the PCP server maps from, to the internal port.
Assigned Public Port
This displays the allocated external port number assigned by the PCP server for the service on the WAN if Allow PCP Port Proposal is enabled. PCP maps from this port number to the internal port number.
Protocol
This is the protocol (TCP or UDP) for port number that identifies a service.
Internal IPv4 Address
This is the LAN device IP address. PCP maps the external IP address to this IP address.
PCP Server
This field displays the status of the PCP mapping request to the PCP server.
Succeeded - The PCP server successfully mapped the external IP address and port to the internal IP address and port.
Failed - The PCP server failed to map the external IP address and port to the internal IP address and port. Make sure to select Allow PCP Port Proposal to allow the PCP server to assign an external IP address and port if the configured ones are not available.
Allow PCP Port Proposal (Y/N)
This displays Y if the PCP server can assign a different external IP address and port to the required ones you configured.
Delete
Select a rule, then click this icon to remove the rule from the Zyxel Device.
Add New Rule Screen
To add a new PCP rule, click Add New Rule. To edit an existing rule, select the rule, then click the Modify icon. The following screen displays.
*Be careful not to configure conflicting mapping between PCP and NAT port forwarding for incoming traffic.
Network Setting > NAT > PCP > Add New Rule
The following table describes the fields in this screen.
Network Setting > NAT > PCP > Add New Rule 
LABEL
Description
Required Internal Port
Enter an internal port number that the PCP server maps to, from the external port.
Required External Port
Enter a proposed external port number that the PCP server maps from, to the internal port.
Protocol
Select the transport layer protocol. Choices are TCP and UDP. See the Service Appendix to see what services require what protocol and port number.
Internal IPv4 Address
Enter the IP address of the LAN device. PCP maps the external IP address to this IP address.
Allow PCP Port Proposal
Select this to allow the PCP server to assign an external IP address and port. If you clear this, PCP mapping will fail if the required ones configured are not available on the PCP server.
Cancel
Click Cancel to exit this screen without saving.
OK
Click OK to save your changes.