Networking: PC-----NE40---------NE5000E-----FTP server
Version of the NE40: V300R002C01B551 (this case is targeted for the V300R002 platform of the NE40)
Networking description: The PC is directly connected to the 100 M electrical interface board of the NE40, which is connected to the 2.5 G port of the NE5000E, which is, in turn, connected to the GE interface of the FTP server. The customer reported that the download speed of the PC was around 70 Mbit/s, and could not reach 100 Mbit/s.
The problem was solved as follows:
1. Checking the configuration, the engineer found no limits to the download speeds at the NE40 and NE5000E sides.
2. After the engineer changed the PC, the problem still existed. Therefore, the problem must not be caused by the PC.
3. Testing the PCs at other nodes, the engineer found no problem with the FTP server.
4. The engineer found no problem with the implementation mechanism of the NE5000E.
5. The engineer found no problem with the MTU value of the links.
6. The engineer found that the PC was directly connected to the NE40 with a 100 M link. The NE40 was connected to the NE5000E with a 2.5 G POS link. The implementation mechanism of the NE40 is as follows: When an NE40 has both high-bandwidth (2.5 G POS) and low-bandwidth (100 M) links, the transmission rate tends to exceed the bandwidth of the outbound interface if the NE40 is not configured with the traffic shaping function (for example, the 2.5 G port tends to receive packets transmitted at a rate of more than 100 Mbit/s). Because the traffic is not shaped, the packets transmitted at a higher rate than the bandwidth of the outbound interface are directly discarded. TCP lowers the speed, causing the average traffic rate to be far lower than the bandwidth of the outbound interface, that is, around 70 Mbit/s. After identifying the cause of the problem, the engineer conducted traffic shaping and found the download speed could reach more than 90 Mbit/s. For the configuration of the V300R002 platform of the NE40, see the appendix.
1. The download speeds were limited at the NE40 and NE5000E sides.
2. The problem was with the PC.
3. The problem was with the FTP server.
4. The implementation mechanism of the NE40 (the cause of the problem addressed here).
5. The implementation mechanism of the NE5000E.
6. Other causes such as the problem with the MTU value of the links.
In the case of the traffic flowing from the high-bandwidth link to the low-bandwidth link, if the download speed is found to be far lower than the bandwidth of the outbound interface, you need to check the traffic shaping function of the device.