Network traffic is related to data packets generated by the ethernet card on the computer, previously we discussed the ethernet card first. The image below shows a linux computer with one ethernet card.
Figure 37. Computer With One Ethernet Card
Data packets sent by other computers are received by the NIC (ethernet card), then forwarded by the ethernet card driver (Network Driver) to the Linux kernel section for processing. This process only regulates data packets that come in or out through one ethernet card. The Linux kernel that is responsible for regulating data flow is called the kernel traffic control.
While the image depicts a Linux computer operated as a gateway or router, the flow of data packets can be arranged bidirectionally (two directions) through NIC0 and NIC1. The Linux gateway is configured to separate traffic from other networks or internet connections provided by the ISP. The connection of the client computer that is divided by NIC1 to the ISP can be controlled, for example, the smtp bandwidth is allocated 64Kbps, & ftp gets 10Kbps bandwidth.
Figure 38. Linux Computer as Router / Gateway
1. Traffic Control Kernel Structure
Basically, the kernel traffic control has 3 parts, the first is the ingress device, namely if the data packet is received by the LAN card, the packet will be processed by the ingress, usually the ingress is used to control upload / uplink traffic. Then the egress device is used to control data packets coming out of the ethernet card, so that download traffic by the client computer can be limited according to the configuration.
Figure 39. Kernel Traffic Control Structure