In a Kubernetes cluster based on a public network, machine A is unable to ping the pods running on machine B.

[WhiteWaterrrr]

I have set up a k8s cluster based on the public network, using the Flannel plugin with VXLAN. Machine A and machine B have different private networks, and A and B can ping each other. However, machine A cannot ping the pod running on machine B. After packet capture analysis, it was found that the pod on machine B received the ping packet and returned the ping packet, but the eth0 network card on machine A did not receive it.

[foursunZero]

hey, guys.Is it convenient for you to display your routing or iptables information? I think there may be no corresponding route.

[Sacerdoss]

It seems like we're running into the same issue after upgrading to debian 12.5 (Kernel 6.1.76-1).

kubeadm version: v1.28.7
flannel version: v0.24.4
cni version: v1.2.0

We have flannel setup in Dualstack mode on a kubeadm cluster using the following net-conf.json:

{
  "Network": "10.244.0.0/16",
  "Backend": {
    "Type": "vxlan"
  },
  "EnableIPv6": true,
  "IPv6Network": "2001:db8:42:0::/56"
}

Interestingly enough the routes were all working directly after the upgrade but after restarting a node the IPv6 routes between pods on different nodes from that restarted node were down. The IPv4 routes however kept working. After restarting the rollout for the kube-flannel daemonset the routes started working again but any node restart will kill them again.

ip -6 route shows the following before and after restart of the node:

2001:db8:42::/64 via 2001:db8:42:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:2::/64 via 2001:db8:42:2:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:4::/64 via 2001:db8:42:4:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:5::/64 via 2001:db8:42:5:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:6::/64 via 2001:db8:42:6:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:7::/64 via 2001:db8:42:7:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:8::/64 via 2001:db8:42:8:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:9:: dev flannel-v6.1 proto kernel metric 256 pref medium
2001:db8:42:9::/64 dev cni0 proto kernel metric 256 pref medium
2001:db8:42:a::/64 via 2001:db8:42:a:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:b::/64 via 2001:db8:42:b:: dev flannel-v6.1 metric 1024 onlink pref medium
2001:db8:42:e::/64 via 2001:db8:42:e:: dev flannel-v6.1 metric 1024 onlink pref medium
<SERVER_IPv6>::/64 dev enp0s31f6 proto kernel metric 256 pref medium
fe80::/64 dev enp0s31f6 proto kernel metric 256 pref medium
fe80::/64 dev flannel.1 proto kernel metric 256 pref medium
fe80::/64 dev flannel-v6.1 proto kernel metric 256 pref medium
fe80::/64 dev cni0 proto kernel metric 256 pref medium
fe80::/64 dev vethb74a35fd proto kernel metric 256 pref medium
fe80::/64 dev veth653394f6 proto kernel metric 256 pref medium
default via fe80::1 dev enp0s31f6 metric 1024 onlink pref medium