Google Certified Associate Cloud Engineer 2020

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OSI layer

routing to righ resource class keep on mention IP address as layer-4…whereas it is layer-3….DNS return layer-3 IP address for URL… TCP works at layer-4.

1 Answers

Hi Anuj.  I think the best explanation of what I mean is this article by the NGINX folks.  In particular, here’s a quote from the end of it:

As this list makes clear, referring to “Layer 4 load balancing” of Internet traffic is a convenient shorthand, but the more accurate term is “Layer 3/4 load balancing” – because the load balancer bases its decision on both the IP addresses of the origin and destination servers (Layer 3) and the TCP port number of the applications (Layer 4). The more exact term for “Layer 7 load balancing” might be “Layer 5 through 7 load balancing” because HTTP combines the functions of OSI Layers 5, 6, and 7.  

And this article by the Envoy Proxy folks has some similar comments throughout.

I’m sorry that you were bugged by my lack of precision in this lecture. 🙂


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