I have Kubernets 1.20.1 cluster with single master and single worker configured with ipvs mode. Using calico CNI calico/cni:v3.16.1. Cluster running on OS RHEL 8 kernel 4.18.0-240.10 with firewalld and selinux disabled.

Running one netshoot pod (10.1.30.130) on master and another pod (10.3.65.132) in worker node.

1. I can ping both pod, in both direction

2. if run the nc command in web server mode, connection is not working. I tried to run nginx on both server, not able get http traffic one server from another server.

Ran the tcpdump on both servers tcpdump -vv -nn -XX -i any host <PODIP> I can see ping traffic going to both nodes, but TCP traffic not reaching the other node.

iptables -vL | grep DROP command not showing any packet drop on both nodes.

I don't know where the TCP traffic getting lost, need some tips to troubleshoot this issue.

Master node iptables-save command output

# Generated by iptables-save v1.8.4 on Sat Jan 16 18:52:50 2021
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:KUBE-MARK-DROP - [0:0]
:KUBE-MARK-MASQ - [0:0]
:KUBE-POSTROUTING - [0:0]
:KUBE-KUBELET-CANARY - [0:0]
:KUBE-SERVICES - [0:0]
:KUBE-FIREWALL - [0:0]
:KUBE-NODE-PORT - [0:0]
:KUBE-LOAD-BALANCER - [0:0]
-A PREROUTING -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
-A POSTROUTING -m comment --comment "kubernetes postrouting rules" -j KUBE-POSTROUTING
-A OUTPUT -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
-A KUBE-MARK-DROP -j MARK --set-xmark 0x8000/0x8000
-A KUBE-MARK-MASQ -j MARK --set-xmark 0x4000/0x4000
-A KUBE-POSTROUTING -m comment --comment "Kubernetes endpoints dst ip:port, source ip for solving hairpin purpose" -m set --match-set KUBE-LOOP-BACK dst,dst,src -j MASQUERADE
-A KUBE-POSTROUTING -m mark ! --mark 0x4000/0x4000 -j RETURN
-A KUBE-POSTROUTING -j MARK --set-xmark 0x4000/0x0
-A KUBE-POSTROUTING -m comment --comment "kubernetes service traffic requiring SNAT" -j MASQUERADE --random-fully
-A KUBE-SERVICES ! -s 10.0.0.0/14 -m comment --comment "Kubernetes service cluster ip + port for masquerade purpose" -m set --match-set KUBE-CLUSTER-IP dst,dst -j KUBE-MARK-MASQ
-A KUBE-SERVICES -m addrtype --dst-type LOCAL -j KUBE-NODE-PORT
-A KUBE-SERVICES -m set --match-set KUBE-CLUSTER-IP dst,dst -j ACCEPT
-A KUBE-FIREWALL -j KUBE-MARK-DROP
-A KUBE-LOAD-BALANCER -j KUBE-MARK-MASQ
COMMIT
# Completed on Sat Jan 16 18:52:50 2021
# Generated by iptables-save v1.8.4 on Sat Jan 16 18:52:50 2021
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:KUBE-FIREWALL - [0:0]
:KUBE-KUBELET-CANARY - [0:0]
:KUBE-FORWARD - [0:0]
-A INPUT -j KUBE-FIREWALL
-A FORWARD -m comment --comment "kubernetes forwarding rules" -j KUBE-FORWARD
-A OUTPUT -j KUBE-FIREWALL
-A KUBE-FIREWALL -m comment --comment "kubernetes firewall for dropping marked packets" -m mark --mark 0x8000/0x8000 -j DROP
-A KUBE-FIREWALL ! -s 127.0.0.0/8 -d 127.0.0.0/8 -m comment --comment "block incoming localnet connections" -m conntrack ! --ctstate RELATED,ESTABLISHED,DNAT -j DROP
-A KUBE-FORWARD -m comment --comment "kubernetes forwarding rules" -m mark --mark 0x4000/0x4000 -j ACCEPT
-A KUBE-FORWARD -m comment --comment "kubernetes forwarding conntrack pod source rule" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A KUBE-FORWARD -m comment --comment "kubernetes forwarding conntrack pod destination rule" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
COMMIT
# Completed on Sat Jan 16 18:52:50 2021
# Generated by iptables-save v1.8.4 on Sat Jan 16 18:52:50 2021
*mangle
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:KUBE-KUBELET-CANARY - [0:0]
COMMIT
# Completed on Sat Jan 16 18:52:50 2021

Worker iptables-save output

# Generated by iptables-save v1.8.4 on Sat Jan 16 18:53:58 2021
*nat
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:KUBE-MARK-DROP - [0:0]
:KUBE-MARK-MASQ - [0:0]
:KUBE-POSTROUTING - [0:0]
:KUBE-KUBELET-CANARY - [0:0]
:KUBE-SERVICES - [0:0]
:KUBE-FIREWALL - [0:0]
:KUBE-NODE-PORT - [0:0]
:KUBE-LOAD-BALANCER - [0:0]
-A PREROUTING -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
-A POSTROUTING -m comment --comment "kubernetes postrouting rules" -j KUBE-POSTROUTING
-A OUTPUT -m comment --comment "kubernetes service portals" -j KUBE-SERVICES
-A KUBE-MARK-DROP -j MARK --set-xmark 0x8000/0x8000
-A KUBE-MARK-MASQ -j MARK --set-xmark 0x4000/0x4000
-A KUBE-POSTROUTING -m mark ! --mark 0x4000/0x4000 -j RETURN
-A KUBE-POSTROUTING -j MARK --set-xmark 0x4000/0x0
-A KUBE-POSTROUTING -m comment --comment "kubernetes service traffic requiring SNAT" -j MASQUERADE --random-fully
-A KUBE-SERVICES ! -s 10.0.0.0/14 -m comment --comment "Kubernetes service cluster ip + port for masquerade purpose" -m set --match-set KUBE-CLUSTER-IP dst,dst -j KUBE-MARK-MASQ
-A KUBE-SERVICES -m addrtype --dst-type LOCAL -j KUBE-NODE-PORT
-A KUBE-SERVICES -m set --match-set KUBE-CLUSTER-IP dst,dst -j ACCEPT
-A KUBE-FIREWALL -j KUBE-MARK-DROP
-A KUBE-LOAD-BALANCER -j KUBE-MARK-MASQ
COMMIT
# Completed on Sat Jan 16 18:53:58 2021
# Generated by iptables-save v1.8.4 on Sat Jan 16 18:53:58 2021
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:KUBE-FIREWALL - [0:0]
:KUBE-KUBELET-CANARY - [0:0]
:KUBE-FORWARD - [0:0]
-A INPUT -j KUBE-FIREWALL
-A FORWARD -m comment --comment "kubernetes forwarding rules" -j KUBE-FORWARD
-A OUTPUT -j KUBE-FIREWALL
-A KUBE-FIREWALL -m comment --comment "kubernetes firewall for dropping marked packets" -m mark --mark 0x8000/0x8000 -j DROP
-A KUBE-FIREWALL ! -s 127.0.0.0/8 -d 127.0.0.0/8 -m comment --comment "block incoming localnet connections" -m conntrack ! --ctstate RELATED,ESTABLISHED,DNAT -j DROP
-A KUBE-FORWARD -m comment --comment "kubernetes forwarding rules" -m mark --mark 0x4000/0x4000 -j ACCEPT
-A KUBE-FORWARD -m comment --comment "kubernetes forwarding conntrack pod source rule" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A KUBE-FORWARD -m comment --comment "kubernetes forwarding conntrack pod destination rule" -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
COMMIT
# Completed on Sat Jan 16 18:53:58 2021
# Generated by iptables-save v1.8.4 on Sat Jan 16 18:53:58 2021
*mangle
:PREROUTING ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]
:KUBE-KUBELET-CANARY - [0:0]
COMMIT
# Completed on Sat Jan 16 18:53:58 2021