Copies for a packet capture, measured on the XGS 136 and both XGS 3300s, 2026-10-25
Discoveries 12 and 17 of the discoveries,
which turned out to be one thing, taken from the source to a product. A capture on a port sees
nothing of a connection once the coprocessor forwards it. The fast path can send the host a copy of
what it forwards: the configuration word's FP_PKT_DUMP bit, 0x010, has it send control message
type 6 (MIRROR_PKT) for every frame - a byte of direction (0 arriving at the port, 1 leaving it), a
reserved byte, the port's tag, then the frame as it crossed that port (the vendor's
cmsg_types.h, struct cmsg_mrr_hdr). The vendor's host hands each copy to the packet capture of
that port and nowhere else. Until now both drivers counted type 6 and let it go: an earlier page
took the bit for a log that wrote nothing
(struck there).
The whole page, with how it was taken and what it does not show: Copies for a packet capture, measured on the XGS 136 and both XGS 3300s, 2026-10-25.
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