Transparent Encryption

Cilium supports the transparent encryption of Cilium-managed host traffic and traffic between Cilium-managed endpoints either using IPsec or WireGuard®:

Known Issues and Workarounds

Egress traffic to not yet discovered remote endpoints may be unencrypted

To determine if a packet needs to be encrypted or not, transparent encryption relies on the same mechanisms as policy enforcement to decide if the destination of an outgoing packet belongs to a Cilium-managed endpoint on a remote node. This means that if an endpoint is allowed to initiate traffic to targets outside of the cluster, it is possible for that endpoint to send packets to arbitrary IP addresses before Cilium learns that a particular IP address belongs to a remote Cilium-managed endpoint or newly joined remote Cilium host in the cluster. In such a case there is a time window during which Cilium will send out the initial packets unencrypted, as it has to assume the destination IP address is outside of the cluster. Once the information about the newly created endpoint has propagated in the cluster and Cilium knows that the IP address is an endpoint on a remote node, it will start encrypting packets using the encryption key of the remote node.

One workaround for this issue is to ensure that the endpoint is not allowed to send unencrypted traffic to arbitrary targets outside of the cluster. This can be achieved by defining an egress policy which either completely disallows traffic to reserved:world identities, or only allows egress traffic to addresses outside of the cluster to a certain subset of trusted IP addresses using toCIDR, toCIDRSet and toFQDN rules. See Layer 3 Examples for more details about how to write network policies that restrict egress traffic to certain endpoints.

Another way to mitigate this issue is to set encryption.strictMode.enabled to true and the expected pod CIDR as encryption.strictMode.cidr. This encryption strict mode enforces that traffic exiting a node to the set CIDR is always encrypted. Be aware that information about new pod endpoints must propagate to the node before the node can send traffic to them.

Encryption strict mode has the following limitations:

  • Only WireGuard encryption is supported.

  • The pod CIDR and therefore the encryption strict mode CIDR must be IPv4. IPv6 traffic is not protected by the strict mode and can be leaked.

  • To disable all dynamic lookups, you must use direct routing mode and the node CIDR and pod CIDR must not overlap. Otherwise, encryption.strictMode.allowRemoteNodeIdentities must be set to true. This allows unencrypted traffic sent from or to an IP address associated with a node identity.