Life of a Packet

This documentation page overviews the life of a packet from an eBPF datapath perspective by explaining three different scenarios.

Video

You can also watch a video explanation of this topic that also explores the tools available within Cilium to help you understand the life of a packet in eCHO Episode 51: Life of a Packet with Cilium.

Endpoint to Endpoint

First we show the local endpoint to endpoint flow with optional L7 Policy on egress and ingress. Followed by the same endpoint to endpoint flow with socket layer enforcement enabled. With socket layer enforcement enabled for TCP traffic the handshake initiating the connection will traverse the endpoint policy object until TCP state is ESTABLISHED. Then after the connection is ESTABLISHED only the L7 Policy object is still required.

Egress from Endpoint

Next we show local endpoint to egress with optional overlay network. In the optional overlay network traffic is forwarded out the Linux network interface corresponding to the overlay. In the default case the overlay interface is named cilium_vxlan. Similar to above, when socket layer enforcement is enabled and a L7 proxy is in use we can avoid running the endpoint policy block between the endpoint and the L7 Policy for TCP traffic. An optional L3 encryption block will encrypt the packet if enabled.

Ingress to Endpoint

Finally we show ingress to local endpoint also with optional overlay network. Similar to above socket layer enforcement can be used to avoid a set of policy traversals between the proxy and the endpoint socket. If the packet is encrypted upon receive it is first decrypted and then handled through the normal flow.

This completes the datapath overview. More BPF specifics can be found in the BPF and XDP Reference Guide. Additional details on how to extend the L7 Policy exist in the Envoy section.