Troubles with netdump(4)

[Mamontov Roman]

Hello.

I try to use netdump(4) option for transmitting kernel dumps to a remote server. 
When  I caused a kernel panic by sysctl debug.kdb.panic I found, that netdumping 
to  remote  server  happens very slow: systat -ifstat on remote side show speed 
around 5KB/s.

On netdump-client side I have:
root at host-1:/home/roman # uname -mv
FreeBSD 12.2-STABLE GENERIC  amd64
root at host-1:/home/roman # 
root at host-1:/home/roman # dumpon -l
em0
root at host-1:/home/roman # cat /etc/rc.local
#!/bin/sh
/sbin/dumpon -c 192.168.7.11 -s 192.168.7.12 em0
root at host-1:/home/roman # ifconfig em0
em0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=81209b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC,VLAN_HWFILTER>
        inet 192.168.7.11 netmask 0xffffff00 broadcast 192.168.7.255
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
root at solution:/home/roman #

On netdumpd-side:
root at host-2:/home/roman # uname -mv
FreeBSD 12.2-STABLE GENERIC  i386
root at host-2:/home/roman # ifconfig em0
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=81209b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC,VLAN_HWFILTER>
        inet 192.168.7.12 netmask 0xffffff00 broadcast 192.168.7.255
        media: Ethernet autoselect (1000baseT <full-duplex>)
        status: active
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
root at solution-old:/home/roman #

Both (host-1 and host-2) have the same stable/12 revision:
# cat /usr/src/.gituprevision
stable/12:879039312
#

When  I  try test network bandwith between host-1 and host-2 with iperf3, I see 
next results:
root at host-1:/home/roman # iperf3 -u -b 0 -c 192.168.7.12
Connecting to host 192.168.7.12, port 5201
[  5] local 192.168.7.11 port 37112 connected to 192.168.7.12 port 5201
[ ID] Interval           Transfer     Bitrate         Total Datagrams
[  5]   0.00-1.00   sec   346 MBytes  2.90 Gbits/sec  248710
[  5]   1.00-2.00   sec   345 MBytes  2.89 Gbits/sec  247750
[  5]   2.00-3.00   sec   345 MBytes  2.90 Gbits/sec  247990
[  5]   3.00-4.00   sec   331 MBytes  2.78 Gbits/sec  238020
[  5]   4.00-5.00   sec   262 MBytes  2.20 Gbits/sec  188260
[  5]   5.00-6.00   sec   345 MBytes  2.89 Gbits/sec  247560
[  5]   6.00-7.00   sec   345 MBytes  2.89 Gbits/sec  247660
[  5]   7.00-8.00   sec   345 MBytes  2.90 Gbits/sec  247980
[  5]   8.00-9.00   sec   342 MBytes  2.87 Gbits/sec  245760
[  5]   9.00-10.00  sec   344 MBytes  2.88 Gbits/sec  246830
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.00  sec  3.27 GBytes  2.81 Gbits/sec  0.000 ms  0/2406520 (0%)  sender
[  5]   0.00-10.07  sec  0.00 Bytes  0.00 bits/sec  0.000 ms  0/0 (0%)  receiver

iperf Done.
root at host-1:/home/roman #

Capturing  traffic  between  host-1 and host-2 not show anything criminal (as I 
understand).

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.

Is  there an particularity in netdump, that can't transmitting crash dumps over 
network faster than 5KB/s? Or this is a "feature" of my test-suite?