Loopback Testing

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Hello Mr. Bryan, et al,

I would like to trouble you with help on loopback testing best practices.

Given there may be a virtual loopback adapter in the NIC, how or will will this have priority over a physical RJ45 loopback plug or give misleading test results?

Additionally, what are best practices when using loopback plugs in fiber optic ports.

Thank you for taking the time to elaborate as neccesary.

Hey @FLM,

Great question, the loopback adapter that you ping with 127.0.0.1 (in fact the 127.0.0.0 network) is for the purposes of testing the OS's ability to use TCP/IP.

An Ethernet loopback adapter wil bring the test down past the Network Layer of the ISO model and test the Data Link and Physical Layer's of the OSI model, testing down to the electrical capabilities of the network adapter itself.

I will get back to you on using a loopback for a fiber optic SFP module.

Thank you very much Mr. Bryan, I appreciate your straight forward explanation!

So just a follow-up question: Does disabling the virtual loopback apapter make any difference when I am troubleshooting with a physical loopback adapter?

@FLM with a physical loopback adapter ping the host IP address and not the loopback address

Thank you for the clarification. I must have confused this with how the virtual loopback adapter and other adapters (TAP, Teredo, etc...) can interfere with your network connectivity testing to the physical NIC.

@FLM you are most welcome, great questions and we are here for you so keep them coming. The Teredo adapter is another virtual adapter that allows an IPv4 client that is behind a network address translation connectivity device (home router, firewall or cable modem), communicate over an IPv6 network.

Thank you for the awesome help. I thoroughly enjoy your courses, very engaging and meaningful!