January 2025 – SDN Clinic

Advanced Linux Routing – VRFs

Linux has been a first class networking citizen for quite a long time now. Every system 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 of separation and features, with PBR being the oldest one and VRFs the most recent addition (starting with Kernel 4.3).

This article is the third part of the Linux Routing series and will provide an overview on Virtual Routing and Forwarding (VRFs) and its applications. The first post in the series about Linux Routing Fundamentals covers 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. The second post on Policy-based routing covers the concepts and plumbing of PBR on Linux. Both are a good read if you don’t feel familiar with these topics and provide knowledge about corner stones referenced here.

Advanced Linux Routing – Policy-based routing

Linux has been a first class networking citizen for quite a long time now. Every system 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 the second part of the Linux Routing series and will provide an overview on Policy-based routing (PBR) and its applications. The previous post about Linux Routing Fundamentals covers 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 is a good read if you don’t feel familiar with these topics. Posts about VRFs and Network Namespaces will follow.

Linux Routing Fundamentals

Linux has been a first class networking citizen for quite a long time now. Every system 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 the first 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.