ECMP Explained: Two Equal Paths, and the Kernel Hashes Flows Across Them

Originally published at https://blog.pathvector.dev/protocol-lab-ecmp-32/ — part of the free Protocol Lab series.

This post is part of Protocol Lab, a free, hands-on series for learning networking protocols by building and breaking them in a container lab. All the lab material — topologies, configs, and scripts — lives in the repo: github.com/pathvector-studio/protocol-lab.

In Lab #31, anycast had routing pick one best path out of many. ECMP (equal-cost multipath) does the opposite trick: when several paths tie, routing keeps all of them and spreads traffic across them — hashing each flow onto one link.

Reading guide: rfc-notes/ecmp.md

Prerequisite: Lab 31: Anycast — One Address, Many Servers, Routing Decides