[tcpdump-workers] Speed specific Link-Layer Header Types for USB 2.0

Michael Richardson mcr at sandelman.ca
Tue Jun 14 10:49:48 EDT 2022


Tomasz Moń via tcpdump-workers wrote:
    >> When low-speed capture is performed, it has to be performed at the leaf
    >> (in graph-theory sense) connection. Full-speed traffic never make it to
    >> the low-speed cables, so the capture will contain only low-speed
    >> packets.

    > Is there anything still to discuss here? I have opened the pull
    > requests [1] [2] few weeks ago. I have also prepared Wireshark [3]
    > change that I would like to merge before Wireshark 4.0 release.

    > I think I have summed up whole discussion in the libpcap commit
    > message. High-speed and Low-speed are pretty much clear, as these links
    > never observe other speed packets. Full-speed is the only disputable
    > one, but I believe the PRE packets are really a corner case that is not
    > worth per-packet speed encoding. If the user has obsolete setup to
    > trigger the corner case in the first place, then such user will
    > definitely know to just capture at the downstream link for low-speed
    > traffic.

I think that Guy and I thought that you'll be better off with a single
LINKTYPE with a subtype header, but if you want to go with three, I don't
object.

--
]               Never tell me the odds!                 | ipv6 mesh networks [
]   Michael Richardson, Sandelman Software Works        |    IoT architect   [
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