The sFlow datagram sent from an agent (the network device) to a collector contains two main types of information: counter samples and flow samples. A flow sample includes the header of a sampled packet. This header contains Layer 2 information, such as source and destination VLAN tags, and Layer 3/4 information. The datagram also includes metadata about the sample itself, such as the agent's address and the specific input and output interface (ifIndex) through which the packet traversed the device.

B. the sending device's serial number: The sFlow agent is identified by its IP address in the datagram, not its hardware serial number.

C. the CRC from the sampled packet: The CRC (Frame Check Sequence) is a Layer 2 trailer field used for error checking and is typically stripped by the hardware before packet processing and sampling occur.

1. Juniper Networks TechLibrary. (2023). Understanding sFlow Technology. "The sFlow agent resides on the switch and packages the following into sFlow datagrams that are sent to the sFlow collector: ... A raw packet header (from the sampled packet). The header contains information such as...source and destination VLANs... The input and output interfaces for the sampled packet."

2. IETF RFC 3176. (September 2001). InMon Corporation's sFlow: A Method for Monitoring Traffic in Switched and Routed Networks. Section 3.4, "Flow Samples", describes the inclusion of the input and output interface numbers. Section 3.4.1, "Raw Packet Header", specifies that the beginning of the packet, including L2 headers, is captured.