Single node, cross pod network working after iptables -P FORWARD ACCEPT, Why ?

[wenerme]

Environmental Info:
K3s Version: v1.28.8+k3s1

Node(s) CPU architecture, OS, and Version:

6.6.23-0-lts #1-Alpine SMP PREEMPT_DYNAMIC Thu, 28 Mar 2024 11:27:43 +0000 x86_64 GNU/Linux

Cluster Configuration:

single

Describe the bug:

after upgrade to alpine 3.19 (the iptable default to nft), k3s cross pod network and external network not working ,using default flannel config, after iptables -P FORWARD ACCEPT, network works again.

Steps To Reproduce:

Expected behavior:

cross pod should just work

Actual behavior:

Additional context / logs:

[brandond]

Do you have a host-based firewall enabled? firewalld, ufw, or so on? Do you have something else configured on your node, such that the default iptables policy is DROP instead of ACCEPT?

[wenerme]

@brandond
AlpineLinux, no ufw, no iptables rules for fw, but I do have multi intferface.

I have eth0, eth4, eth5, flannel choose eth4, I think maybe this is the problem.