Systems and methods for transmitting content to a client via a communication network are provided. An insertion server, running within a firewall device associated with a private IP network, detects establishment of a transport communication protocol connection between a client associated with the network and a destination located external to the network by examining packets as they pass through the network and pass by the insertion server. A content request of an application protocol initiated by the client and directed to the destination is observed by the insertion server. The content request is negated by the insertion server by causing a canceling message of the transport communication protocol to be sent to the destination. Unsolicited content is caused to be selected for delivery to the client by the insertion server. The unsolicited content is sent by the insertion server to the client via the application protocol.