Troubles with netdump(4)

[Mamontov Roman]

>> Next  I  try  netdumping  to  another  FreeBSD-host  (virtual machine on VMWare 
>> hypervisor):
>> root at host-3:~ # uname -mv
>> FreeBSD 12.2-STABLE r369412 GENERIC  amd64
>> root at host-3:~ # ifconfig em0
>> em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>>        options=81009b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,VLAN_HWFILTER>
>>        inet 192.168.7.18 netmask 0xffffff00 broadcast 192.168.7.255
>>        media: Ethernet autoselect (1000baseT <full-duplex>)
>>        status: active
>>        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
>> root at host-3:~ #
>> 
>> And netdumping to this host are still slow (~the same 5KB/s). 
>> 
>> Next step another FreeBSD-host (virtual machine on VirtualBox hypevisor):
>> root at host-4:~ # uname -mv
>> FreeBSD 12.2-STABLE r369412 GENERIC  amd64
>> root at host-4:~ # ifconfig em0
>> em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
>>        options=81009b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,VLAN_HWFILTER>
>>        inet 192.168.7.19 netmask 0xffffff00 broadcast 192.168.7.255
>>        media: Ethernet autoselect (1000baseT <full-duplex>)
>>        status: active
>>        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
>> root at host-4:~ #
>> 
>> Both (host-3 and host-4) are installed from FreeBSD-12.2-STABLE-amd64-20210304-r369412-bootonly.iso
>> When  I  caused  a  kernel panic by sysctl debug.kdb.panic on host-4, netdumping to 
>> host-3 show the same 5 KB/s.
> netdump requires explicit acks from the other side.
> Could you try dumping the exchange between the dumping host and the server to
> verify that acks are sent immediately after receiving the next chunk?
Sure. There is a dump:
https://disk.yandex.ru/d/i27n1m-I80DaEg
What should be tuned: netdumpd, netdumpd-host or something else?

Now I can't completely done netdump: there frequenly error:
** DUMP FAILED (ERROR 60) **
Cannot dump: unknown error (error=60).

and  panic inside iflib: https://pastebin.com/1BTTjGLJ