Hello everyone 
Kubernetes version: 1.27
Cloud being used: public cloud
Installation method: binary
Host OS: centos 7.9.2
Kube-Proxy Mode : iptables
My enviroment have 3 machine.
master 10.36.21.100
node1 10.36.21.101
node2 10.36.21.102
I have chosen Flannel as the CNI tool for my cluster. The podSubnet of my cluster and the network CIDR of Flannel are both set as 10.244.0.0/16. I am using Flannel version 0.22.0 in vxlan mode. Subsequently, I deployed a test pod with NodePort 30800 on node1. When I use the command [curl 10.36.21.100:30800], I cannot get any response. However, when I try to curl 10.36.21.101:30800, I do get a response.
In order to resolve the issue, I performed various checks on my machine, including verifying the firewalld, iptables, and Flannel settings. However, I haven’t been able to identify any problems with my cluster.
Next, I used the nmap command to check my ports and I was able to see the 30800 port on both my master and node 2. The output is as follows:
[root@test-node1 bin]# nmap 10.36.21.100 -p 30000-31000
Starting Nmap 6.40 ( http://nmap.org ) at 2023-07-26 15:51 CST
Nmap scan report for test-master (10.36.21.176)
Host is up (0.00035s latency).
Not shown: 93 closed ports
PORT STATE SERVICE
30800/tcp filtered unknown
After inspecting the logs of Flannel, kube-apiserver, and kube-proxy, I found everything to be normal.
I’m quite perplexed by this issue and I would greatly appreciate any assistance you could provide."