[Bug 254036] Linksys USB3GIG fails to ping with large packets (maxfragsperpacket was increased)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254036

--- Comment #9 from Mike Belanger <mibelanger at qnx.com> ---
I configured a fresh system with FreeBSD 12.2 RELEASE r366954 amd64.  (It's an
old DELL PC.)

The remote side is a Linux PC (192.168.10.2) running Ubuntu 16.04.
I am using the onboard interface. (RTL8111/8168/8411 PCI Express Gigabit
Ethernet Controller).

To allow large UDP packets on FreeBSD, I changed net.inet.ip.maxfragsperpacket
from 16 to 64.
(The default for net.inet6.ip6.maxfragsperpacket is 64).

Everything is from the perspective of the FreeBSD PC.  All pings originate from
FreeBSD.

A large ping from the on board interface is successful.
I also ran tests with 4 different USB devices.  

test10. Cisco Linksys USB300M (successful)
Vendor                     : 0x0b95 (ASIX Elec. Corp.)
Product                    : 0x7720 (AX88x72A)

test11. D-Link DUB-E100 (successful)
Vendor                     : 0x2001 (D-Link Corporation)
Product                    : 0x3c05 (DUB-E100)

test12. Startech USB3200SPT (fails fo 32k.)
Vendor                     : 0x0b95 (ASIX Elec. Corp.)
Product                    : 0x1790 (AX88179)

test13. Linksys USB3GIG (fails for 64k)
Vendor                     : 0x13b1 (Linksys)
Product                    : 0x0041 (Linksys USB3GIGV1)

The following commands were issued:
ping -c1 192.168.1.2
ping -c1 -s 8000 192.168.1.2
ping -c1 -s 32000 192.168.1.2
ping -c1 -s 64000 192.168.1.2

I tested with additional devices to highlight that some devices work and some
do not.
The first two were successful.  The second two were not.  I originally
suspected that this issue was specific to the USB3GIG as there was a Linux
patch for this device.

The pcap traces on the local side were captured a second time, as I terminated
tcpdump with a SIGKILL out of habit.  This resulted in truncated files so I
recaptured the local traces a second time.  So they may not match exactly to
with the respective capture for the Linux side, but the Linux traces do not
show any missing packets.

test11b - successful pings with D-Link device
test12b - shows missing fragments for ping with size 32000.
test13b - shows missing fragments for ping with size 64000.  32000 was
successful.
test12remote - captured in linux side.  all packets present.
test13remote - captured on Linux side.  all packets present.

Le me know if I can provide more information.

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