How to analyse k3s subnetting

k3s, k3OS, and k3d
1

I am facing networking issues when using an k3s agent in WSL 2.

I now need to analyse how flannel translates cluster ip addresses to public ip addresses. This is how you would do it with flannel in k8s:

admin@ip-172-20-33-102:~$ etcdctl ls /coreos.com/network/subnets
/coreos.com/network/subnets/100.96.1.0-24
/coreos.com/network/subnets/100.96.2.0-24
/coreos.com/network/subnets/100.96.3.0-24

admin@ip-172-20-33-102:~$ etcdctl get /coreos.com/network/subnets/100.96.2.0-24
{"PublicIP":"172.20.54.98"}`

Source: https://blog.laputa.io/kubernetes-flannel-networking-6a1cb1f8ec7c

I know there is no etcd in k3s but sqlite. Where do I find those translations there?

Many thanks in advance and BR,
Martin

2

When using k3s in default settings, it is using flannel for networking and vxlan as backend. As there is no etcd database available it stores its cluster ip address to network ip address translation in ARP and FDB entries as stated here: https://github.com/coreos/flannel/blob/4ff77dc7c35851913587f7daccf25d754e77aa65/backend/vxlan/vxlan.go.

A very nice explanation is provided here: https://medium.com/@anilkreddyr/kubernetes-with-flannel-understanding-the-networking-part-2-78b53e5364c7

So whenever you have networking related problems within k3s and standard flannel it might be worth to have a look at the FDB entries of your flannel interface. I have been able to solve my problems from there.