Application of RJ45 short circuit ring on gigabit Nic

Application of RJ45 short circuit ring on gigabit Nic

1. Topic Origin
For those who often work on multiple operating systems, using Windows as the host system with Vmware Workstation is already a standard Workstation. I personally traveled back and forth between Windows and Linux and used the notebook configuration as Windows 7 as the host, VMWare Workstation 9 to install the Virtual Machine CentOS and OpenBSD. Virtual Machine network connection is set to bridge, so that the virtual machine is more like a real host in the LAN. However, this bridging method requires the physical network adapter to be truly connected to the local area network (I heard that the new version of VWmware is not required? I cannot experiment on my own ). In this way, when the network environment is left, the network communication between the virtual machine and the host machine and the virtual machine cannot be established.

There are two solutions: one is "soft method", that is, through the software virtual a switch environment, I did not find the appropriate software to complete; the other is through the RJ45 short circuit ring, enable the physical Nic to automatically collect data. This article introduces the second method, which is simple and effective without changing the software environment.
2. Principle of RJ45 short Link Ring
RJ45 connector PIN number definition:

2.1 Mbit/s Ethernet RJ45 interface pin signal definition number
Signal Definition
1
TX +
2
TX-
3
RX +
4
Unused
5
Unused
6
RX-
7
Unused
8
Pin signal definition number for 2.2 Gigabit Ethernet RJ45 interface not used
Signal Definition
1
BI_D1 +
2
BI_D1-
3
BI_D2 +
4
BI_D3 +
5
BI_D3-
6
BI_D2-
7
BI_D4 +
8
BI_D4-

2.3 self-received spontaneous connection
Send the send pin and the corresponding receive pin can be directly short-circuited. For 100MbRJ-45, connect 1-3, 2-6, and gigabit network RJ45, 1-3, 2-6, 4-7, 5-8 respectively. Of course, the Gigabit method also applies to MB, but it only wastes two lines. The crystal headers are as follows:

3. Problems and Solutions on gigabit NICs
According to the above method, the loop crystal head has been tested and found to work normally on a MB Nic. If it is a Windows system, the network is connected. It does not work on a gigabit Nic and the network cable is disconnected.

After searching on the Internet (here I would like google again, it is difficult to find the answer to technical questions on Baidu), I finally find the reason. Each Gigabit Nic has a Near End Cross Talk (NEXT) function. Enabling this function will make the short-path ring unavailable. The problem is that many Nic drivers do not provide a way to disable this function. I have not found any options to disable this function in the BIOS. please let us know.

Although you cannot close NEXT, you can solve the problem by manually adjusting the NIC to work in MB full duplex mode. In Windows, right-click the NIC attribute.

Here is a short article about NEXT: