Encrypting traffic between nodes with IPsec

Overview

IPsec protects traffic in an OKD cluster by encrypting the communication between all master and node hosts that communicate using the Internet Protocol (IP).

This topic shows how to secure communication of an entire IP subnet from which the OKD hosts receive their IP addresses, including all cluster management and pod data traffic.

Because OKD management traffic uses HTTPS, enabling IPsec encrypts management traffic a second time.

This procedure must be repeated on each master host, then node host, in your cluster. Hosts that do not have IPsec enabled will not be able to communicate with a host that does.

Encrypting hosts

Prerequisites

  • Ensure that libreswan 3.15 or later is installed on cluster hosts. If opportunistic group functionality is required, then libreswan version 3.19 or later is required.

  • This topic describes an IPsec configuration that requires 62 bytes. If the cluster is operating on an Ethernet network with a maximum transmission unit (MTU) value of 1500 bytes then the SDN MTU value must be changed to 1388 bytes to allow for the overhead of IPsec and the SDN encapsulation. Complete the following procedure to change the MTU for the nodes in your cluster:

    1. Edit each of the following ConfigMaps: node-config-master, node-config-infra, node-config-compute.

      1. Run the following command to edit the ConfigMap. Replace <config_map> with the name of the ConfigMap to edit.

        1. # oc edit cm <config_map> -n openshift-node

      2. Update the mtu parameter to an MTU size sufficient for the IPsec overhead, such as 1388 bytes:

        1. networkConfig:
        2.   mtu: 1388
  1. 2.  Remove the SDN interface by running the following command. Replace `<ovs_pod_name>` with the name of the OVS pod.
  3.     ```
  4.     # oc exec <ovs_pod_name> -- ovs-vsctl del-br br0
  5.     ```
  7. 3.  For each node in your cluster, complete the following actions:
  9.     1.  Confirm that the updated MTU value is saved to the `/etc/origin/node/node-config.yaml` file.
  11.     2.  Restart the SDN and OVS pods by running the following commands:
  13.         ```
  14.         # oc delete pod -n openshift-sdn -l=app=ovs
  15.         # oc delete pod -n openshift-sdn -l=app=sdn
  16.         ```

Configuring certificates for IPsec

You can generate RSA keys suitable for IPsec by using the OKD internal certificate authority (CA). The internal CA has the common name (CN) value set to openshift-signer.

  1. Run the following commands to generate the RSA certificates on the master node:

    1. # export CA=/etc/origin/master
    3. # oc adm ca create-server-cert \
    4.   --signer-cert=$CA/ca.crt --signer-key=$CA/ca.key \
    5.   --signer-serial=$CA/ca.serial.txt \
    6.   --hostnames='<hostname>' \ (1)
    7.   --cert=<hostname>.crt \ (1)
    8.   --key=<hostname>.key (1)
    1Replace <hostname> with the fully qualified domain name (FQDN) of the node.

  2. Use openssl to combine the client certificate, CA certificate, and private key files into a PKCS#12 file, which is a common file format for multiple certificates and keys:

    1. # openssl pkcs12 -export \
    2.   -in <hostname>.crt \ (1)
    3.   -inkey <hostname>.key \ (1)
    4.   -certfile  /etc/origin/master/ca.crt \
    5.   -passout pass: \
    6.   -out <hostname>.p12 (1)
    1Replace with the fully qualified domain name (FQDN) of the node.

  3. For each node in your cluster, securely transfer the file that you created for the host in the previous step, and then import the PKCS#12 file into the libreswan certificate database.

    The -W option is left empty because no password is assigned to the PKCS#12 file, as it is only temporary.

    1. # ipsec initnss
    2. # pk12util -i <hostname>.p12 -d sql:/etc/ipsec.d -W ""
    3. # rm <hostname>.p12

Creating the libreswan IPsec policy

After ensuring that the necessary certificates are imported into the libreswan certificate database, create a policy that uses them to secure communication between hosts in your cluster.

If you are using libreswan 3.19 or later, then opportunistic group configuration is recommended. Otherwise, explicit connections are required.

Configuring the opportunistic group

The following configuration creates two libreswan connections. The first encrypts traffic using the OKD certificates, while the second creates exceptions to the encryption for cluster-external traffic.

  1. Place the following into the /etc/ipsec.d/openshift-cluster.conf file:

    1. conn private
    2.     left=%defaultroute
    3.     leftid=%fromcert
    4.     # our certificate
    5.     leftcert="NSS Certificate DB:<cert_nickname>" (1)
    6.     right=%opportunisticgroup
    7.     rightid=%fromcert
    8.     # their certificate transmitted via IKE
    9.     rightca=%same
    10.     ikev2=insist
    11.     authby=rsasig
    12.     failureshunt=drop
    13.     negotiationshunt=hold
    14.     auto=ondemand
    16. conn clear
    17.     left=%defaultroute
    18.     right=%group
    19.     authby=never
    20.     type=passthrough
    21.     auto=route
    22.     priority=100
    1Replace <cert_nickname> with the certificate nickname from step one.

  2. Tell libreswan which IP subnets and hosts to apply each policy using policy files in /etc/ipsec.d/policies/, where each configured connection has a corresponding policy file. So, in the example above, the two connections, private and clear, each have a file in /etc/ipsec.d/policies/.

    /etc/ipsec.d/policies/private must contain the IP subnet of your cluster, which your hosts receive IP addresses from. By default, this causes all communication between hosts in the cluster subnet to be encrypted if the remote host’s client certificate authenticates against the local host’s Certificate Authority certificate. If the remote host’s certificate does not authenticate, all traffic between the two hosts will be blocked.

    For example, if all hosts are configured to use addresses in the 172.16.0.0/16 address space, your private policy file would contain 172.16.0.0/16. Any number of additional subnets to encrypt may be added to this file, which results in all traffic to those subnets using IPsec as well.

  3. Unencrypt the communication between all hosts and the subnet gateway to ensure that traffic can enter and exit the cluster. Add the gateway to the /etc/ipsec.d/policies/clear file:

    1. 172.16.0.1/32

    Additional hosts and subnets may be added to this file, which will result in all traffic to these hosts and subnets being unencrypted.

Configuring the explicit connection

In this configuration, each IPsec node configuration must explicitly list the configuration of every other node in the cluster. Using a configuration management tool such as Ansible to generate this file on each host is recommended.

Do not manually edit the node-config.yaml file. To modify a node in your cluster, update the node configuration maps as needed.

This configuration also requires the full certificate subject of each node to be placed into the configuration for every other node.

  1. Use openssl to read this subject from the node’s certificate:

    1. # openssl x509 \
    2.   -in /path/to/client-certificate -text | \
    3.   grep "Subject:" | \
    4.   sed 's/[[:blank:]]*Subject: //'

  2. Place the following lines into the /etc/ipsec.d/openshift-cluster.conf file on each node for every other node in the cluster:

    1. conn <other_node_hostname>
    2.         left=<this_node_ip> (1)
    3.         leftid="CN=<this_node_cert_nickname>" (2)
    4.         leftrsasigkey=%cert
    5.         leftcert=<this_node_cert_nickname> (2)
    6.         right=<other_node_ip> (3)
    7.         rightid="<other_node_cert_full_subject>" (4)
    8.         rightrsasigkey=%cert
    9.         auto=start
    10.         keyingtries=%forever
    1Replace <this_node_ip> with the cluster IP address of this node.
    2Replace <this_node_cert_nickname> with the node certificate nickname from step one.
    3Replace <other_node_ip> with the cluster IP address of the other node.
    4Replace <other_node_cert_full_subject> with the other node’s certificate subject from just above. For example: “O=system:nodes,CN=openshift-node-45.example.com”.

  3. Place the following in the /etc/ipsec.d/openshift-cluster.secrets file on each node:

    1. : RSA "<this_node_cert_nickname>" (1)
    1Replace <this_node_cert_nickname> with the node certificate nickname from step one.

Configuring the IPsec firewall

All nodes within the cluster need to allow IPsec related network traffic. This includes IP protocol numbers 50 and 51 as well as UDP port 500.

For example, if the cluster nodes communicate over interface eth0:

  1. -A OS_FIREWALL_ALLOW -i eth0 -p 50 -j ACCEPT
  2. -A OS_FIREWALL_ALLOW -i eth0 -p 51 -j ACCEPT
  3. -A OS_FIREWALL_ALLOW -i eth0 -p udp --dport 500 -j ACCEPT

IPsec also uses UDP port 4500 for NAT traversal, though this should not apply to normal cluster deployments.

Starting and enabling IPsec

  1. Start the ipsec service to load the new configuration and policies, and begin encrypting:

    1. # systemctl start ipsec

  2. Enable the ipsec service to start on boot:

    1. # systemctl enable ipsec

Optimizing IPsec

See the Scaling and Performance Guide for performance suggestions when encrypting with IPsec.

Troubleshooting

When authentication cannot be completed between two hosts, you will not be able to ping between them, because all IP traffic will be rejected. If the clear policy is not configured correctly, you will also not be able to SSH to the host from another host in the cluster.

You can use the ipsec status command to check that the clear and private policies have been loaded.