Transmission Control Protocol (TCP/IP or TCP) is a communication standard for programs and computing devices to exchange messages over a network.
TCP sends packets across the internet and ensures that the data was successfully delivered. TCP is a reliable, error-checked delivery protocol.
TCP ensures the security and integrity of the data being transmitted by first establishing a connection between the client and server, and then performing a series of handshakes to validate the connection before tranmision begins. TCP also breaks data into smaller packets to ensure data integrity.
HTTP, SMTP, and SSH are examples of protocols that run over TCP connections.
Droplet network traffic restricts TCP and UDP traffic on port 11211 inbound from external networks (due to the Memcached amplification attacks in March 2018).
When creating custom rules, you will have to specify the protocol which is either TCP or UDP.
To learn more about configuring rules, see How to Configure Firewall Rules.
TCP balancing is available for applications that do not use HTTP. For example, deploying a load balancer in front of a database cluster like Galera would allow you to spread requests across all available machines.
By default, load balancers ignores the
Connection: keep-alive headers returned by target Droplets. You can configure the load balancer to use fewer active TCP connections by enabling the backend keepalive setting.
For more information about TCP traffic, see How to Balance TCP Traffic.