In the previous chapter, we explored how Cilium allocates IP addresses to pods. With each pod now assigned an IP, the next logical step is to understand how traffic flows between them. This is the role of the Cilium datapath: the set of technologies Cilium uses to process, route, and forward packets within a Kubernetes cluster.
In this chapter, we’ll examine how packets are delivered both within and across nodes, how different routing models work, and how encapsulation protocols like VXLAN and Geneve come into play when native routing isn’t possible. You can find all the YAML manifests you will use in this chapter in the chapter05 directory of the book’s GitHub repository.
We’ll begin with the simplest case (intranode, for communication between pods on the same node), then move on to internode traffic (connectivity between pods located on different nodes) and the differences between native and overlay modes (Figure 5-1).
Figure 5-1. Intranode versus internode communication
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