A loopback connector provides the network interface driver the necessary link for testing, while maintaining isolation from a live network. netlbtest cannot run if the network interface is connected to a live network, however the link must be up. To run netlbtest, a loopback connector must be connected to the Ethernet interface. Even though the netlbtest does not depend on the network interface configuration status of the Ethernet interface, the interface should be brought down with the ifconfig command (refer to the ifconfig(1M) man page) to avoid erroneous messages. You must have the Ethernet card and the device driver installed, a loopback connector in place, and Intervention mode enabled before running netlbtest. Each time the packet sent is selected from a different starting point of the data buffer, so that any two consecutively transmitted packets will not be the same.ĭo not run nettest and netlbtest at the same time or the tests may fail. If an error occurs (for example, packet mismatch or timeout), an error message indicating the type of error, its probable cause(s) and recommended action(s) is displayed on the SunVTS console.The data sent out is generated by a random number generator, and put into a data buffer. The test generates and sends out the desired number of packets (a tunable parameter) and expects to receive the same number of packets through the loopback interface, external or internal. For the purpose of this test, a packet is defined as an Ethernet header followed by the Ethernet data payload (refer to the IEEE 802.3z standard). The netlbtest uses DLPI RAW mode to talk to the device driver. It runs in loopback (external/internal) mode.
These include eri (the Ethernet device in the RIO chip) and ge (Gigabit Ethernet), and ce (GigaSwift Ethernet).
Ethernet loopback cable drivers#
It provides functional test coverage of the devices whose device drivers support the Ethernet loopback test. The netlbtest replaces the gemtest previously included in SunVTS.
This is known as spanning tree.Chapter 40 Ethernet Loopback Test ( netlbtest) Some other switches will turn the loop back cable into a redundant link. Newer switches usually have built in loop back protection, whereby they will disable a port if it suspects a loop back. This issue tends to affect older infrastructure only. Are there a group of lights flashing repeatedly and in time with each other? The odd group flash can be ignored, but a constant group of lights flashing together is worth investigating. It can also be useful to observe the activity lights on the switch as well. If you have managed network switches, the diagnostic section of the web interface may give an insight into a loop back situation and highlight the offending ports. Have any wall ports been activated? Have any new switches or hubs been added to the network? Examine the cabling and look for any cables with both ends plugged into a switch. Review any changes made to the network recently. This results in broadcast data getting looped through the switch(es) and holding back genuine data transfers by eating up a huge amount of bandwidth.
Ethernet loopback cable Patch#
If a network patch cable has both ends inserted into either the same switch or a neighbouring switch that's part of the same LAN, you can create what's called a loop back.
You may also receive timeout errors when trying to access network resources. This can be signified by excessive logon times, slow access via mapped drives and poor Internet performance. You may experience degraded performance on your local area network. Network performance can be severely impacted by the introduction of a network loop. Loop back causing poor performance on local area network
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