Hi Guy,

Thanks! If we choose to change libpcap, I think both Wireshark and Npcap
driver are not required to be modified any more then. I will test it when
the code is submitted:)


Cheers,
Yang

On Thu, Sep 15, 2016 at 11:20 AM, Guy Harris <[email protected]> wrote:

> On Sep 13, 2016, at 10:03 PM, Yang Luo <[email protected]> wrote:
>
> > But the problem is, libpcap  (which is used by Npcap) only supports the
> value 23 in the BPF filter code.
>
> This is a problem in more ways than one.
>
> For example, if you're running on FreeBSD, and are reading a pcap or
> pcapng file from NetBSD, and it has loopback packets, a filter checking for
> IPv6 packets won't work, because it'll be looking for the FreeBSD AF_INET6
> (28), but IPv6 packets will have NetBSD's AF_INET6 (24).
>
> So, when reading a capture file, the filter should check for *all* of the
> possible AF_INET6 values, because there's no way to determine, from the
> file, which AF_INET6 value was used.
>
> When doing a live capture, it should, if possible, just use whatever the
> capture mechanism provides, to avoid doing other checks.
>
> I'll fix this up; for now, just keep using 24 - it's not as if any code
> that wants to read an AF_NULL pcap file can rely on its OS's AF_INET6 being
> the packet type value *anyway*, it has to check for all platform values
> (which both tcpdump and Wireshark do).
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