rtnetlink

Package rtnetlink allows the kernel's routing tables to be read and altered. Network routes, IP addresses, Link parameters, Neighbor setups, Queueing disciplines, Traffic classes and Packet classifiers may all be controlled. It is based on netlink messages.

A convenient, high-level API wrapper is available using package rtnl.

The base rtnetlink library explicitly only exposes a limited low-level API to rtnetlink. It is not the intention (nor wish) to create an iproute2 replacement.

Debugging and netlink errors

Unfortunately the errors generated by the kernels netlink interface are not very great.

When in doubt about your message structure it can always be useful to look at the message send by iproute2 using strace -f -esendmsg /bin/ip or similar.

Another (and possibly even more flexible) way would be using nlmon and wireshark. nlmod is a special kernel module which allows you to capture all netlink (not just rtnetlink) traffic inside the kernel. Be aware that this might be overwhelming on a system with a lot of netlink traffic.

# modprobe nlmon
# ip link add type nlmon
# ip link set nlmon0 up

At this point use wireshark or tcpdump on the nlmon0 interface to view all netlink traffic.

Have a look at the examples for common uses of rtnetlink.

If you have any questions or you'd like some guidance, please join us on Gophers Slack in the #networking channel!