What is a correct statement related to BIG TCP, an eBPF-based feature in Cilium?

Technical explanation

BIG TCP permits the Linux networking stack to process packets larger than the traditional approximately 64-KiB limit represented by the IP length field while the packets remain inside the host. IPv6 BIG TCP uses a temporary Hop-by-Hop header carrying the larger internal length, while IPv4 BIG TCP sets tot_len to zero and uses the socket buffer length internally. Before transmission, packets are segmented into sizes suitable for the physical network. C therefore identifies the problem BIG TCP addresses.

Option A is false because Cilium’s documentation explicitly states that BIG TCP does not require network-interface MTU changes. The larger objects exist inside the software networking stack and are segmented before appearing on the wire.

Option B reverses the intended performance effect. Larger internal GSO and GRO packets reduce repeated stack traversal, lowering CPU utilization and generally improving throughput and latency. Option D is also false: Generic Segmentation Offload and Generic Receive Offload are fundamental to BIG TCP’s operation. Cilium increases their maximum sizes when BIG TCP is enabled. The source mentions TSO, but the documented mechanism is principally described through GSO and GRO.

Official references

Cilium Performance Tuning and BIG TCP

Study Guide topic: BIG TCP, GSO/GRO, packet-length limits, and performance.