Chapter 13. Using the Stream Control Transmission Protocol (SCTP) As a cluster administrator, you can use the Stream Control Transmission Protocol (SCTP) on a bare-metal cluster. 13.1. Support for SCTP on OpenShift Container Platform As a cluster administrator, you can enable SCTP on the hosts in the cluster. On Red Hat Enterprise Linux CoreOS (RHCOS), the SCTP module is disabled by default. SCTP is a reliable message based protocol that runs on top of an IP network. When enabled, you can use SCTP as a protocol with pods, services, and network policy. A Service object must be defined with the type parameter set to either the ClusterIP or NodePort value. 13.1.1. Example configurations using SCTP protocol You can configure a pod or service to use SCTP by setting the protocol parameter to the SCTP value in the pod or service object. In the following example, a pod is configured to use SCTP: apiVersion: v1 kind: Pod metadata: namespace: project1 name: example-pod spec: containers: - name: example-pod ... ports: - containerPort: 30100 name: sctpserver protocol: SCTP In the following example, a service is configured to use SCTP: apiVersion: v1 kind: Service metadata: namespace: project1 name: sctpserver spec: ... ports: - name: sctpserver protocol: SCTP port: 30100 targetPort: 30100 type: ClusterIP In the following example, a NetworkPolicy object is configured to apply to SCTP network traffic on port 80 from any pods with a specific label: kind: NetworkPolicy apiVersion: networking.k8s.io/v1 metadata: name: allow-sctp-on-http spec: podSelector: matchLabels: role: web ingress: - ports: - protocol: SCTP port: 80 13.2. Enabling Stream Control Transmission Protocol (SCTP) As a cluster administrator, you can load and enable the blacklisted SCTP kernel module on worker nodes in your cluster. Prerequisites Install the OpenShift CLI ( oc ). Access to the cluster as a user with the cluster-admin role. Procedure Create a file named load-sctp-module.yaml that contains the following YAML definition: apiVersion: machineconfiguration.openshift.io/v1 kind: MachineConfig metadata: name: load-sctp-module labels: machineconfiguration.openshift.io/role: worker spec: config: ignition: version: 3.2.0 storage: files: - path: /etc/modprobe.d/sctp-blacklist.conf mode: 0644 overwrite: true contents: source: data:, - path: /etc/modules-load.d/sctp-load.conf mode: 0644 overwrite: true contents: source: data:,sctp To create the MachineConfig object, enter the following command: USD oc create -f load-sctp-module.yaml Optional: To watch the status of the nodes while the MachineConfig Operator applies the configuration change, enter the following command. When the status of a node transitions to Ready , the configuration update is applied. USD oc get nodes 13.3. Verifying Stream Control Transmission Protocol (SCTP) is enabled You can verify that SCTP is working on a cluster by creating a pod with an application that listens for SCTP traffic, associating it with a service, and then connecting to the exposed service. Prerequisites Access to the internet from the cluster to install the nc package. Install the OpenShift CLI ( oc ). Access to the cluster as a user with the cluster-admin role. Procedure Create a pod starts an SCTP listener: Create a file named sctp-server.yaml that defines a pod with the following YAML: apiVersion: v1 kind: Pod metadata: name: sctpserver labels: app: sctpserver spec: containers: - name: sctpserver image: registry.access.redhat.com/ubi9/ubi command: ["/bin/sh", "-c"] args: ["dnf install -y nc && sleep inf"] ports: - containerPort: 30102 name: sctpserver protocol: SCTP Create the pod by entering the following command: USD oc create -f sctp-server.yaml Create a service for the SCTP listener pod. Create a file named sctp-service.yaml that defines a service with the following YAML: apiVersion: v1 kind: Service metadata: name: sctpservice labels: app: sctpserver spec: type: NodePort selector: app: sctpserver ports: - name: sctpserver protocol: SCTP port: 30102 targetPort: 30102 To create the service, enter the following command: USD oc create -f sctp-service.yaml Create a pod for the SCTP client. Create a file named sctp-client.yaml with the following YAML: apiVersion: v1 kind: Pod metadata: name: sctpclient labels: app: sctpclient spec: containers: - name: sctpclient image: registry.access.redhat.com/ubi9/ubi command: ["/bin/sh", "-c"] args: ["dnf install -y nc && sleep inf"] To create the Pod object, enter the following command: USD oc apply -f sctp-client.yaml Run an SCTP listener on the server. To connect to the server pod, enter the following command: USD oc rsh sctpserver To start the SCTP listener, enter the following command: USD nc -l 30102 --sctp Connect to the SCTP listener on the server. Open a new terminal window or tab in your terminal program. Obtain the IP address of the sctpservice service. Enter the following command: USD oc get services sctpservice -o go-template='{{.spec.clusterIP}}{{"\n"}}' To connect to the client pod, enter the following command: USD oc rsh sctpclient To start the SCTP client, enter the following command. Replace <cluster_IP> with the cluster IP address of the sctpservice service. # nc <cluster_IP> 30102 --sctp

Commands:
apiVersion: v1 kind: Pod metadata: namespace: project1 name: example-pod spec: containers: - name: example-pod ports: - containerPort: 30100 name: sctpserver protocol: SCTP
apiVersion: v1 kind: Service metadata: namespace: project1 name: sctpserver spec: ports: - name: sctpserver protocol: SCTP port: 30100 targetPort: 30100 type: ClusterIP
kind: NetworkPolicy apiVersion: networking.k8s.io/v1 metadata: name: allow-sctp-on-http spec: podSelector: matchLabels: role: web ingress: - ports: - protocol: SCTP port: 80
apiVersion: machineconfiguration.openshift.io/v1 kind: MachineConfig metadata: name: load-sctp-module labels: machineconfiguration.openshift.io/role: worker spec: config: ignition: version: 3.2.0 storage: files: - path: /etc/modprobe.d/sctp-blacklist.conf mode: 0644 overwrite: true contents: source: data:, - path: /etc/modules-load.d/sctp-load.conf mode: 0644 overwrite: true contents: source: data:,sctp
oc create -f load-sctp-module.yaml
oc get nodes
apiVersion: v1 kind: Pod metadata: name: sctpserver labels: app: sctpserver spec: containers: - name: sctpserver image: registry.access.redhat.com/ubi9/ubi command: ["/bin/sh", "-c"] args: ["dnf install -y nc && sleep inf"] ports: - containerPort: 30102 name: sctpserver protocol: SCTP
oc create -f sctp-server.yaml
apiVersion: v1 kind: Service metadata: name: sctpservice labels: app: sctpserver spec: type: NodePort selector: app: sctpserver ports: - name: sctpserver protocol: SCTP port: 30102 targetPort: 30102
oc create -f sctp-service.yaml
apiVersion: v1 kind: Pod metadata: name: sctpclient labels: app: sctpclient spec: containers: - name: sctpclient image: registry.access.redhat.com/ubi9/ubi command: ["/bin/sh", "-c"] args: ["dnf install -y nc && sleep inf"]
oc apply -f sctp-client.yaml
oc rsh sctpserver
nc -l 30102 --sctp
oc get services sctpservice -o go-template='{{.spec.clusterIP}}{{"\n"}}'
oc rsh sctpclient
nc <cluster_IP> 30102 --sctp