Calico does not use an overlay for communication between Pods.  It leverages a direct layer3 routed network which will route the Pod payload protocol without encapsulation.  The only exception is inter-host communication that uses an IPinIP tunnel, so those will carry an extra outer IP header.

-Matt

From: "Jones, Bruce E" <bruce.e.jones@intel.com>
Date: Tuesday, December 17, 2019 at 1:31 PM
To: "starlingx-discuss@lists.starlingx.io" <starlingx-discuss@lists.starlingx.io>
Subject: [Starlingx-discuss] Customer Question - TCP between pods?

Forgive me for asking what may be an obvious question.  I was meeting with a customer today and the question came up – does StarlingX use/enable TCP between pods?  Their experience was with K3S/Flannel which uses UDP.

Thank you!

      brucej