Terminal line sequence adaptive functions and applications from network faults

Readers who have several years of experience with network administrators know that when selecting a network cable, you must pay attention to the line sequence problem. Our common network cable is divided into two types: the main line, the other is the anti-line. Generally, the main line is used to connect a vswitch to a vro, And the vswitch to connect a PC. The reverse line is used to connect a vswitch to a vswitch, A vro to a vro, a PC to connect a PC, and a vro to a PC. However, in recent years, network equipment manufacturers have developed a feature called line sequence adaptive. This feature can be used to automatically detect the network cable types connected to their own interfaces and automatically adjust the network cable types. However, in actual use, I have encountered a network fault because I believe this line sequence is adaptive too much. Here I will write down the whole process of the problem and share it with it168 readers, I hope you will be cautious when selecting a network connection device.

Fault Cause and troubleshooting:

I also know that the switch has this adaptive function, so you only need to carry a positive network cable with you. However, in the last network debugging, I was really embarrassed. This is the case: I received a call from a subordinate department and said that two routers could not communicate normally. So I took the device and rushed to the subordinate Department. On one of the vro settings interfaces, I found that the Ethernet port connected to the other vro was not activated at all, as if I had not connected any network cable. Actually, a network cable is used to connect the lan1 Ethernet interface of two routers. Why? I know that anti-line should be used for the connection between the router and the router according to the normal situation. However, with the development of technology, the ports have the adaptive jumper function, you can connect to these devices either through the reverse line or through the main line. However, for insurance purposes, I still found a back line to replace the original main line. I did not expect the problem to be solved. The interfaces of Both routers are in the active connection status, and the network is not blocked.

Fault analysis:

So why is the network going back to normal after the original main line is replaced with the reverse line? It can be noted that it is not feasible to connect two routers with a positive line. It seems that the adaptive jumper does not appear on every device. The port of the Huawei 2621 router used by the author does not support adaptive jumper. Therefore, when connecting devices, do not assume that all interfaces are adaptive forward and backward lines, especially router interfaces. Most of the interfaces do not support adaptive jumper functions, most vswitches support this sort of line adaptive. Finally, I also asked the network administrator of a subsidiary company whether the network cable was moved. The answer was that the network cable of the two routers was taken elsewhere in the emergency response a few days ago, while the original network cable was a reverse line, because the network administrator of a subsidiary company thinks that the router port can be adaptive, a main line is used for connection.

Under what circumstances can I adapt to the line sequence:

Some readers may ask why some router interfaces support Adaptive Line sequence? How can I identify whether my devices support this function? Next we will introduce this knowledge.

The so-called jumper adaptive or Adaptive Line sequence, the correct name should be port MDI/mdix automatic adaptation, only support port MDI/mdix automatic adaptation of the port to allow users from any port to connect to the workstation, servers or other vro switches can work normally without changing the common twisted pair connection mode. How can I confirm that my device port supports jumper adaptive function? The following methods are used.

View User Manual:

See which ports in the manual indicate that auto is supported
MDI/mdix adaptive. Remember that only auto is supported.
This function is available only when MDI/mdix is adaptive. Otherwise, we still need to connect different devices according to the conventional connection method.

View panel buttons:

Generally, there is an MDI/mdix button on the switch device, but some routers also have this button. We can switch between the MDI and mdix working modes by pressing this button. So that the same two devices can be connected by a different line sequence of the network cable, the main line and the back line to connect the device only need to pass
The MDI/mdix button can be switched to meet the requirements. Of course, in actual connection, we can work in the MDI mode first. If there is a network problem or the port is not activated, switch to the mdix mode.

View console commands:

Some devices can use internal commands to switch the port between MDI and mdix. The specific command is as follows -- [Quidway-Ethernet0/1] MDI
{Alibaba SS | normal | auto}

If you enter "MDI auto", the auto MDI/mdix adaptive function is enabled.
In the mdix connection mode
Normal is to use the standard MDI connection mode. Of course, in order to facilitate our daily work and maintenance, I suggest you directly enter the MDI
Auto command, so no matter what type of router your cable is, it will automatically adapt to the line sequence as traditional switches.

For most vswitches, ports support auto
MDI/mdix adaptive function, but the router interface is not necessarily, so we should not take it for granted that all devices support auto
The MDI/mdix adaptive function also requires special attention when selecting a connection network cable. Do not use it blindly without line or line. Connecting with the standard method can help us solve faults quickly and reduce unnecessary problems.

Why vrouters do not support self-adaptation:

The author called Huawei 3com and asked why Huawei 3Com
2621 vrouters do not provide automatic cable sequence adaptation. The answer is that this is to make it easier for users. Generally, the vro is connected to a vswitch and the vswitch can automatically adapt to the route sequence. Therefore, you do not need to add the vro again. In addition, adding a feature will increase the corresponding cost. Huawei 3Com does not add a line sequence adaptive feature on the router, which also reduces the product cost from the user's perspective. In addition, Cisco routers do not support this sort of line adaptive. However, according to the introduction of Huawei 3Com staff, new products such as the MSR router of Huawei 3Com already have the terminal line sequence adaptive function, which makes it easier and more convenient for users to connect to network devices.

Summary:

This fault tells us that the more expensive the device is, the more powerful the function is. According to common sense, the price of the router is much higher than that of the common switch. Therefore, its port should be able to support line sequence adaptive, however, the reality is not in line with the theory. The two lanports on the 2621 router of Huawei 3Com do not support this sort of line adaptive. We must follow the conventional cable connection rules when connecting devices.