Final answer:
To allow FTP traffic through a Layer 3 device, configure Access Control Lists or firewall rules to permit traffic on FTP ports 20 and 21. Additionally, for active mode FTP, ensure the firewall allows incoming connections initiated by the server.
Step-by-step explanation:
To allow FTP traffic to pass through a Layer 3 device, such as a router or a firewall, you would configure Access Control Lists (ACLs) or firewall rules. An Access Control List is a set of rules that is used to filter network traffic based on IP protocols, IP addresses, and port numbers. FTP typically uses port 21 for control messages and port 20 for data transfer. Therefore, to enable FTP traffic, you must allow traffic on these ports.
Additionally, if the Layer 3 device is a firewall and it supports stateful inspection or deep packet inspection, you might need to enable specific features or rules that cater to the FTP protocol, which can sometimes use dynamic ports for data transfer. For active mode FTP, the server will initiate connections back to the client, which requires proper handling by the firewall to allow these connections.
In summary, you would need to configure the ACLs or firewall rules to permit inbound and outbound traffic on the necessary FTP ports. This setup ensures that FTP traffic can freely flow through the Layer 3 device without being blocked.