Kubernetes' networking model assumes that every Pod has its own IP address and that Pods can communicate with other Pods across nodes without requiring network address translation (NAT). That makes B correct. This is one of Kubernetes' core design assumptions and is typically implemented via CNI plugins that provide flat, routable Pod networking (or equivalent behavior using encapsulation/routing).
This model matters because scheduling is dynamic. The scheduler can place Pods anywhere in the cluster, and applications should not need to know whether a peer is on the same node or a different node. With the Kubernetes network model, Pod-to-Pod communication works uniformly: a Pod can reach any other Pod IP directly, and nodes can reach Pods as well. Services and DNS add stable naming and load balancing, but direct Pod connectivity is part of the baseline model.
Option A is incorrect because Pods can communicate directly using Pod IPs even without Services (subject to NetworkPolicies and routing). Services are abstractions for stable access and load balancing; they are not the only way Pods can communicate. Option C is incorrect because Pod IPs are not limited to visibility "inside a Pod"; they are routable within the cluster network. Option D is misleading: Services are often used by Pods (clients) to reach a set of Pods (backends). "Service IP used for communication between Services" is not the fundamental model; Services are virtual IPs for reaching workloads, and "Service-to-Service communication" usually means one workload calling another via the target Service name.
A useful way to remember the official model: (1) all Pods can communicate with all other Pods (no NAT), (2) all nodes can communicate with all Pods (no NAT), (3) Pod IPs are unique cluster-wide. This enables consistent microservice connectivity and supports higher-level traffic management layers like Ingress and service meshes.
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