Mac-mini-6:~ User$ sudo pfctl -vnf /etc/pf.conf

pfctl: Use of -f option, could result in flushing of rules
present in the main ruleset added by the system at startup.
See /etc/pf.conf for further details.

scrub-anchor "/*" all fragment reassemble
nat-anchor "/*" all
rdr-anchor "/*" all
anchor "/*" all
anchor "/*" all
dummynet-anchor "/*" all

Loading anchor com.apple from /etc/pf.anchors/com.apple
anchor "/*" all
anchor "/*" all

Loading anchor plex-ssdp.block from /etc/pf.anchors/plex-ssdp.block
block drop out quick on en0 proto udp from any to any port = 1900
block drop out quick on en1 proto udp from any to any port = 1900


Mac-mini-6:~ User$ sudo pfctl -vnf /etc/pf.anchors/plex-ssdp.block
pfctl: Use of -f option, could result in flushing of rules
present in the main ruleset added by the system at startup.
See /etc/pf.conf for further details.

block drop out quick on en0 proto udp from any to any port = 1900
block drop out quick on en1 proto udp from any to any port = 1900

$sudo tcpdump -n -s0 port 1900 and udp
IP 192.168.2.11.53952 > 239.255.255.250.1900: UDP, length 101

Mac-mini-6:~ User$ sudo pfctl -vvv -s all
No ALTQ support in kernel
ALTQ related functions disabled
TRANSLATION RULES:
@0 nat-anchor "com.apple/*" all
  [ Owner : nil          Priority : 0     ]
  [ Evaluations: 46275     Packets: 0         Bytes: 0           States: 0     ]
  [ Inserted: uid 0 pid 511 ]
@0 rdr-anchor "com.apple/*" all
  [ Owner : nil          Priority : 0     ]
  [ Evaluations: 105227    Packets: 0         Bytes: 0           States: 0     ]
  [ Inserted: uid 0 pid 511 ]

FILTER RULES:
@0 scrub-anchor "com.apple/*" all fragment reassemble
  [ Owner : nil          Priority : 0     ]
  [ Evaluations: 180874    Packets: 0         Bytes: 0           States: 0     ]
  [ Inserted: uid 0 pid 511 ]
@0 anchor "com.apple/*" all
  [ Owner : nil          Priority : 0     ]
  [ Evaluations: 105266    Packets: 0         Bytes: 0           States: 0     ]
  [ Inserted: uid 0 pid 511 ]
@1 anchor "plex-ssdp.block/*" all
  [ Owner : nil          Priority : 0     ]
  [ Evaluations: 105266    Packets: 0         Bytes: 0           States: 0     ]
  [ Inserted: uid 0 pid 511 ]

DUMMYNET RULES:
@0 dummynet-anchor "com.apple/*" all
  [ Owner : nil          Priority : 0     ]
  [ Evaluations: 0         Packets: 0         Bytes: 0           States: 0     ]
  [ Inserted: uid 0 pid 511 ]

INFO:
Status: Enabled for 0 days 03:42:26           Debug: Urgent

listening on pktap, link-type PKTAP (Apple DLT_PKTAP), capture size 262144 bytes
12:07:51.775753 IP 192.168.2.11.53952 > 239.255.255.250.1900: UDP, length 101
12:07:51.782263 IP 192.168.2.12.1900 > 192.168.2.11.53952: UDP, length 289
12:07:51.783203 IP 192.168.2.15.1900 > 192.168.2.11.53952: UDP, length 289
12:07:51.783207 IP 192.168.2.3.1900 > 192.168.2.11.53952: UDP, length 247
12:07:51.783208 IP 192.168.2.6.1900 > 192.168.2.11.53952: UDP, length 447
12:07:51.783209 IP 192.168.2.3.1900 > 192.168.2.11.53952: UDP, length 251
12:07:51.783210 IP 192.168.2.6.1900 > 192.168.2.11.53952: UDP, length 449
12:07:51.783211 IP 192.168.2.15.1900 > 192.168.2.11.53952: UDP, length 275
12:07:51.783211 IP 192.168.2.12.1900 > 192.168.2.11.53952: UDP, length 275
12:07:51.783212 IP 192.168.2.16.1900 > 192.168.2.11.53952: UDP, length 272
12:07:51.783213 IP 192.168.2.12.1900 > 192.168.2.11.53952: UDP, length 287
12:07:51.784444 IP 192.168.2.15.1900 > 192.168.2.11.53952: UDP, length 287