Tracing a Packet Journey Using Linux Tracepoints, perf and eBPF

I’ve been looking for a low level Linux network debugging tool for quite some time. Linux allows to build complex networks running directly on the host, using a combination of virtual interfaces and network namespaces. When something goes wrong, troubleshooting is rather tedious. If this is a L3 routing issue, mtr has a good chance of being of some help. But if this is a lower level issue, I typically end up manually checking each interface / bridge / network namespace / iptables and firing up a couple of tcpdumps as an attempt to get a sense of what’s going on. If you have no prior knowledge of the network setup, this may feel like a maze.

What I’d need is a tool which could tell me “Hey, I’ve seen your packet: It’s gone this way, on this interface, in this network namespace”.

Basically, what I’d need is a mtr for L2.

Does not exist? Let’s build one!

Read more at Yet Another Enthusiast Blog


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