Linux has been a first class networking citizen for quite a long time now. Every box running a Linux kernel out of the box has at least three routing tables and is supporting multiple mechanisms for advanced routing features from policy based routing (PBR), to VRFs(-lite), and network namespaces (NetNS). Each of these provide different levels or separation and features, with PBR being the oldest one and VRFs the most recent addition (starting with Kernel 4.3).
This article is part of the Linux Routing series and will provide an overview of the basics and plumbings of Linux routing tables, what happens when an IP packet is sent from or through a Linux box, and how to figure out why. It’s the baseline for future articles on PBR, VRFs, and NetNSes, their differences as well and applications.
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