Cannot identify process of listening port 600/tcp6

[BBlister]

Dear,

I am trying to identify what process is listening on port 600/tcp6.

I have tried:
# lsof -n -P | grep :600
#
--nothing

# sockstat -a | grep :600
?        ?          ?     ?  tcp6   *:600                 *:*


# netstat -an | grep 600
tcp6       0      0 *.600                  *.*                    LISTEN


I can connect to this port, but I receive no output to my commands:
# telnet ::1 600
Trying ::1...
Connected to localhost.
Escape character is '^]'.
help
?
test


My uname:
# uname -a
FreeBSD XXX 11.2-RELEASE-p8 FreeBSD 11.2-RELEASE-p8 #0: Tue Jan  8 21:35:12
UTC 2019     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC 
amd64

# kldstat
Id Refs Address            Size     Name
 1   37 0xffffffff80200000 20647c8  kernel
 2    1 0xffffffff82266000 2d40     coretemp.ko
 3    1 0xffffffff82421000 6fc4     tmpfs.ko
 4    1 0xffffffff82428000 41f0     linprocfs.ko
 5    2 0xffffffff8242d000 2d28     linux_common.ko
 6    1 0xffffffff82430000 195c     linsysfs.ko
 7    4 0xffffffff82432000 20198    ipfw.ko
 8    1 0xffffffff82453000 24a0     if_tap.ko
 9    1 0xffffffff82456000 107a0    dummynet.ko
10    1 0xffffffff82467000 13f0     ipdivert.ko
11    1 0xffffffff82469000 21b0     ipfw_nat.ko
12    1 0xffffffff8246c000 a4f2     libalias.ko



Perhaps this is a kernel module, but which? Is this a strange rootkit? I did
not reboot the machine, because I would like to locate the offending process
first. This box runs nginx and rtorrent.

Thanks!



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