ufw

Main commands:

# show apps available profiles
sudo ufw app list

# allow available profile
sudo ufw allow OpenSSH

sudo ufw enable
sudo ufw status

Log analysis:

Oct 20 11:02:27 bbb kernel: [ 7980.724380] [UFW BLOCK]
IN=eth1 OUT=

# MAC |server (2x6) |client (2x6)     |
MAC=   00:1e:8c:7b:cf:ca:fc:75:16:56:e4:78:08:00

# client
SRC=192.168.35.67

# server
DST=192.168.35.10

LEN=60
TOS=0x00
PREC=0x00
TTL=64
ID=61984
DF

# type of protocol TCP/UDP
PROTO=TCP

SPT=37252

# PORT
DPT=80

WINDOW=29200
RES=0x00
SYN
URGP=0