The problem of fast forwarding of one router:
Users make ADSL dial with R2600. After the dial-up, downloading speed is very slow and dial-up bandwidth is 4M. Actual rate only reaches few K. Users dial with PC and can reach full rate. It is possible that there is virus or attack on the router. Log on the device and the operation of the router is normal and there is no error packet on the port. Check port configuration and mss of external network is changed. Set mss as default. Downloading rate is improved, but there is great difference with theory rate. Through further analysis, users close fast forwarding on the port. Open fast forwarding and downloading rate recovers.
Generally, when we handle loss, delay, webpages not opened, mtu, mss and IP fast forwarding are taken into consideration.
About fast forwarding:
Fast forwarding is operated in interruption. If there is no fast forwarding, it is normal forwarding and can support all services. Normal forwarding needs advanced receiving queue and is handled in packet handling through task scheduling. Special services such as GRE, IPSec need join in the queue and schedule one task. It can support many services but the performance is reduced. For fast forwarding, it removes L2 encapsulation and checks route after receiving the packet. If it is the interface of the board, it encapsulates and sends directly. If it is other boards, it sends the packet to other boards through communication between the boards. There is no cost of queue and task scheduling. The performance and delay are improved. The interruption is similar to that of PC. After the interface card receives the packet, the hardware that informs CPU to handle through interruption controller is interrupted. The interruption can influence the operation of present task. It hops to response function. After the function is executed, execute interrupted task. Interruption handling means the response function finishes the handling of the packet and fast forwarding is not used. The function analyzes L2 header and put it into th queue. And then it is finished.