Talos Linux Ingress Firewall is a simple and effective way to limit network access to the services running on the host, which includes both Talos standard services (e.g. apid and kubelet), and any additional workloads that may be running on the host. Talos Linux Ingress Firewall doesn’t affect the traffic between the Kubernetes pods/services, please use CNI Network Policies for that.
Note: If you use another tool that provides node level network filtering (e.g. Cilium Host Firewall) it may take precedence in the nftables chain and bypass OS level rules.

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Configuration

Ingress rules are configured as extra documents NetworkDefaultActionConfig and NetworkRuleConfig in the Talos machine configuration: 
apiVersion: v1alpha1
kind: NetworkDefaultActionConfig
ingress: block
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: kubelet-ingress
portSelector:
  ports:
    - 10250
  protocol: tcp
ingress:
  - subnet: 172.20.0.0/24
    except: 172.20.0.1/32
The first document configures the default action for ingress traffic, which can be either accept or block, with the default being accept. If the default action is set to accept, then all ingress traffic will be allowed, unless there is a matching rule that blocks it. If the default action is set to block, then all ingress traffic will be blocked, unless there is a matching rule that allows it. With either accept or block, traffic is always allowed on the following network interfaces:
  • lo
  • siderolink
  • kubespan
In block mode:
  • ICMP and ICMPv6 traffic is also allowed with a rate limit of 5 packets per second
  • traffic between Kubernetes pod/service subnets is allowed (for native routing CNIs)
The second document defines an ingress rule for a set of ports and protocols on the host. The NetworkRuleConfig might be repeated many times to define multiple rules, but each document must have a unique name. The ports field accepts either a single port or a port range: 
portSelector:
  ports:
    - 10250
    - 10260
    - 10300-10400
The protocol might be either tcp or udp. The ingress specifies the list of subnets that are allowed to access the host services, with the optional except field to exclude a set of addresses from the subnet.
Note: incorrect configuration of the ingress firewall might result in the host becoming inaccessible over Talos API. It is recommended that the configuration be applied in --mode=try to ensure it is reverted in case of a mistake.
The following rules improve the security of the cluster and cover only standard Talos services. If there are additional services running with host networking in the cluster, they should be covered by additional rules. In block mode, the ingress firewall will also block encapsulated traffic (e.g. VXLAN) between the nodes, which needs to be explicitly allowed for the Kubernetes networking to function properly. Please refer to the documentation of the CNI in use for the specific ports required. Some default configurations are listed below:
  • Flannel, Calico: vxlan UDP port 4789
  • Cilium: vxlan UDP port 8472
In the examples we assume the following template variables to describe the cluster:
  • $CLUSTER_SUBNET, e.g. 172.20.0.0/24 - the subnet which covers all machines in the cluster
  • $CP1, $CP2, $CP3 - the IP addresses of the controlplane nodes
  • $VXLAN_PORT - the UDP port used by the CNI for encapsulated traffic

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Controlplane

In this example Ingress policy:
  • apid and Kubernetes API are wide open
  • kubelet and trustd API are only accessible within the cluster
  • etcd API is limited to controlplane nodes
apiVersion: v1alpha1
kind: NetworkDefaultActionConfig
ingress: block
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: kubelet-ingress
portSelector:
  ports:
    - 10250
  protocol: tcp
ingress:
  - subnet: $CLUSTER_SUBNET
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: apid-ingress
portSelector:
  ports:
    - 50000
  protocol: tcp
ingress:
  - subnet: 0.0.0.0/0
  - subnet: ::/0
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: trustd-ingress
portSelector:
  ports:
    - 50001
  protocol: tcp
ingress:
  - subnet: $CLUSTER_SUBNET
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: kubernetes-api-ingress
portSelector:
  ports:
    - 6443
  protocol: tcp
ingress:
  - subnet: 0.0.0.0/0
  - subnet: ::/0
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: etcd-ingress
portSelector:
  ports:
    - 2379-2380
  protocol: tcp
ingress:
  - subnet: $CP1/32
  - subnet: $CP2/32
  - subnet: $CP3/32
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: cni-vxlan
portSelector:
  ports:
    - $VXLAN_PORT
  protocol: udp
ingress:
  - subnet: $CLUSTER_SUBNET

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Worker

  • kubelet and apid API are only accessible within the cluster
apiVersion: v1alpha1
kind: NetworkDefaultActionConfig
ingress: block
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: kubelet-ingress
portSelector:
  ports:
    - 10250
  protocol: tcp
ingress:
  - subnet: $CLUSTER_SUBNET
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: apid-ingress
portSelector:
  ports:
    - 50000
  protocol: tcp
ingress:
  - subnet: $CLUSTER_SUBNET
---
apiVersion: v1alpha1
kind: NetworkRuleConfig
name: cni-vxlan
portSelector:
  ports:
    - $VXLAN_PORT
  protocol: udp
ingress:
  - subnet: $CLUSTER_SUBNET

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Learn More

Talos Linux Ingress Firewall uses nftables to perform the filtering. With the default action set to accept, the following rules are applied (example): 
table inet talos {
  chain ingress {
    type filter hook input priority filter; policy accept;
    iifname { "lo", "siderolink", "kubespan" }  accept
    ip saddr != { 172.20.0.0/24 } tcp dport { 10250 } drop
    meta nfproto ipv6 tcp dport { 10250 } drop
  }
}
With the default action set to block, the following rules are applied (example): 
table inet talos {
  chain ingress {
    type filter hook input priority filter; policy drop;
    iifname { "lo", "siderolink", "kubespan" }  accept
    ct state { established, related } accept
    ct state invalid drop
    meta l4proto icmp limit rate 5/second accept
    meta l4proto ipv6-icmp limit rate 5/second accept
    ip saddr { 172.20.0.0/24 } tcp dport { 10250 }  accept
    meta nfproto ipv4 tcp dport { 50000 } accept
    meta nfproto ipv6 tcp dport { 50000 } accept
  }
}
The running nftable configuration can be inspected with talosctl get nftableschain -o yaml. The Ingress Firewall documents can be extracted from the machine config with the following command: talosctl get mc v1alpha1 -o yaml | yq .spec | yq 'select(.kind == "NetworkDefaultActionConfig"),select(.kind == "NetworkRuleConfig" )'