Why test the TCP/IP stack?

Why test the TCP/IP stack?...I mean, by what I learnt, pinging 127.0.0.1 tests the the TCP/IP stack from to to bottom, i.e.: from Application to ....errrr...Physical layer?...or does it stop at layer 3 of the OSI model (Internet layer). I'm basing myself on this:

The loopback interface does not require a physical interface to function. A packet sent to a loopback interface is not processed by a network adapter but is otherwise processed as normal by the host's TCP/IP stack.

..according to this, the TCP stack doesn't include layers 1 and 2 (the NIC)...so if I'm right, testing the TCP/IP stack is testing layers 3 to 7 (Network to Application)...so all this layers are in "software in the RAM" right?

So you're basically testing the TCP/IP protocol in software in the RAM (I mean excluding the firmware in the NIC).

Am I right? I'd welcome any clarifications.

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Comments

JDMurray

The loopback address range of 127.0.0.0/8 is entirely local to the host. All loopback traffic is handled only by the host's TCP/IP software in OSI Layers 3 through 7. Layers 1 & 2 are only needed for network traffic actually ingressing/egressing to the physical network, which loopback traffic never does.