How to: Layer 4 load balancing
Layer 4 load balancers look at info at the [transport layer](#communication) to decide how to distribute requests.  Generally, this involves the source, destination IP addresses, and ports in the header, but not the contents of the packet.  Layer 4 load balancers forward network packets to and from the upstream server, performing [Network Address Translation (NAT)](https://www.nginx.com/resources/glossary/layer-4-load-balancing/).