podmtu

Podmtu is a term used in the context of container and pod networking to describe the maximum transmission unit (MTU) configured for traffic within a pod. It refers to the largest packet size that can be transmitted within the pod network without requiring fragmentation. The term is not a formal standard, but it appears in documentation and operational discussions as a practical reference for configuring network paths inside containerized environments.

In practice, podmtu is influenced by multiple layers of the network stack. The underlying host interfaces have their own MTU values, and many container setups use overlay or tunneling networks (such as VXLAN or GRE) that add encapsulation headers. Those headers effectively reduce the end-to-end payload size that can be carried by a packet. As a result, the podmtu is typically lower than the maximum MTU of the physical network. In non-overlay environments, a podmtu close to the standard 1500 bytes is common, while overlay-based deployments often require a reduced value, commonly around 1400 to 1450 bytes, to accommodate header overhead without triggering fragmentation.

Configuration and management of podmtu are usually handled by the container orchestration platform and its network plugin (CNI). Administrators may set the MTU at the plugin level or adjust host interface MTUs to ensure consistency across the path. Correct sizing helps prevent fragmentation, improves performance, and reduces the risk of packet loss due to MTU mismatches. If misconfigured, systems may experience intermittent connectivity issues, degraded throughput, or PMTU discovery failures.

See also: MTU, Path MTU Discovery, Kubernetes, Docker, CNI plugins, VXLAN.