GUI tool

/etc/init.d/network-manager restart


ls -l /sys/class/net/   # E.g.: ens3 -> ../../devices/pci0000:00/0000:00:03.0/virtio0/net/ens3
ip addr show dev eth1

ifconfig ens7 up
ip addr add dev eth0 && ip link set eth0 up

ip addr flush dev eth0
ifconfig eth0 && dhclient

ip route add default via
ip route show table all


auto enp1s0
iface enp1s0 inet dhcp


  version: 2
  renderer: networkd / NetworkManager

    enp1s0: {}
#   comments
      dhcp4: yes
      addresses: []

      accept-ra: no
      id: 10
      link: enp2s0

    # no need to set vlan in VM
      dhcp4: yes
      openvswitch: {}
      interfaces: [ vlan.10 ]
    br1: {}
      openvswitch: {}
      dhcp4: yes

setup ovs manually

netplan try

  • reverting ... not supported, directly run: netplan apply
  • other errors: netplan generate or netplan --debug apply

Port listening

# netstat -lntup | grep 8888
tcp        0      0  *               LISTEN      5119/python         
tcp6       0      0 :::8888                 :::*                    LISTEN      5119/python

# ss -lntup | grep 8888
tcp   LISTEN  0       128          *      users:(("jupyter-noteboo",pid=5119,fd=7))                                      
tcp   LISTEN  0       128                       [::]:8888            [::]:*      users:(("jupyter-noteboo",pid=5119,fd=6))


tcpdump -i any port 27017
nmap -sV -p6379


ip tuntap add mode tap dev tap1
        tap1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
        link/ether a2:05:e8:7f:d9:e8 brd ff:ff:ff:ff:ff:ff

ip tuntap add mode tun dev tun1
        tun1: <POINTOPOINT,MULTICAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 500


ethtool -k ens3 | grep offload              # list Features
ethtool -K ens3 gro off gso off tso off     # set tcp-segmentation-offload, generic-segmentation/receive-offload

disable ipv6

echo "net.ipv6.conf.all.disable_ipv6=1"  >> /etc/sysctl.conf
sysctl  -p



table / chain

iptables -t nat -L # filter(default), nat, mangle, raw and security
iptables -t nat -F ...  # empty chain rules
iptables -t nat -X ...  # delete empty chain

iptables -t nat -L -n -x -v # --numeric IP/Port --exact packet and byte counters --verbose
iptables -L --line-numbers
iptables -D INPUT 2



iptables -I INPUT -i docker0 -j ACCEPT
iptables -I INPUT -s localhost -j ACCEPT

iptables -A INPUT --dport 81 -j DROP
iptables -A INPUT -p tcp -m multiport  --dport 3306,6379 -j DROP
iptables -A INPUT -p udp --dport 161 -j ACCEPT


    _____                                     _____
    /     \                                   /     \
PREROUTING -->[Routing ]----------------->POSTROUTING----->
    \D-NAT/     [Decision]                    \S-NAT/
                    |                            ^
                    |                            |
                    --------> Local Process ------

Masquerading is a specialized form of SNAT
Port forwarding, load sharing, and transparent proxying are all forms of DNAT.


modprobe nf_log_ipv4
sysctl net.netfilter.nf_log.2=nf_log_ipv4
iptables -t raw -A OUTPUT -p icmp -j TRACE
iptables -t raw -A PREROUTING -p icmp -j TRACE
vi /var/log/kern.log

tcpdump -i any icmp

Log manually

iptables_log_INPUT_DROP() {
    iptables -N LOGGING
    iptables -A INPUT -j LOGGING
    iptables -A LOGGING -m limit --limit 2/min -j LOG --log-prefix "IPTables-Dropped: " --log-level 4
    iptables -A LOGGING -j DROP

Transparent Proxy

iptables -t nat -N TP
iptables -t nat -I TP -p tcp --dport 4433 -j RETURN  # bypass Port

iptables -t nat -A TP -d -j RETURN
iptables -t nat -A TP -d -j RETURN
iptables -t nat -A TP -d -j RETURN
iptables -t nat -A TP -d -j RETURN
iptables -t nat -A TP -d -j RETURN
iptables -t nat -A TP -d -j RETURN
iptables -t nat -A TP -d -j RETURN
iptables -t nat -A TP -d -j RETURN

# Anything else should be redirected to Dokodemo-door's local port
iptables -t nat -A TP -p tcp -j REDIRECT --to-ports 20088
iptables -t nat -I OUTPUT -p tcp -j TP
iptables -t nat -I PREROUTING -p tcp -j TP

# Add any UDP rules
iptables -t mangle -N TP
iptables -t mangle -A TP -p udp --dport 53 -j TPROXY --on-port 20088 --tproxy-mark 0x01/0x01
iptables -t mangle -A PREROUTING -j TP

iptables -t mangle -N TP_MARK
iptables -t mangle -A TP_MARK -p udp --dport 53 -j MARK --set-mark 1
iptables -t mangle -A OUTPUT -j TP_MARK

ip route add local default dev lo table 100
ip rule add fwmark 1 lookup 100

ip rule del fwmark 1 lookup 100 # disable UDP

iptables frontend

CentOS firewall-cmd

firewall-cmd --permanent --zone=public \
--add-rich-rule="rule family="ipv4" \
source address="" \
port protocol="tcp" port="4567" accept"

firewall-cmd --zone=public --add-port=4433/tcp --permanent
firewall-cmd --zone=public --add-port=4433/udp--permanent
firewall-cmd --reload
firewall-cmd --list-all

service firewalld stop 

Ubuntu - ufw

sudo ufw allow 11200:11299/tcp
sudo ufw status verbose
sudo ufw disable

ip rule

Priority: 0, Selector: match anything, Action: lookup routing
        table local (ID 255).  The local table is a special routing
        table containing high priority control routes for local and
        broadcast addresses.

Priority: 32766, Selector: match anything, Action: lookup
        routing table main (ID 254).  The main table is the normal
        routing table containing all non-policy routes. This rule may
        be deleted and/or overridden with other ones by the

Priority: 32767, Selector: match anything, Action: lookup
        routing table default (ID 253).  The default table is empty.
        It is reserved for some post-processing if no previous default
        rules selected the packet.  This rule may also be deleted.

# cat /etc/iproute2/rt_tables

    # reserved values
    255 local
    254 main
    253 default
    0   unspec
    # local
    #1  inr.ruhep


IPVS - an advanced layer-4 load balancing solution´╝î NAT/Direct Routing/IP Tunneling

Virtual routing and forwarding
multiple independent routing tables working simultaneously on the same router or switch Think of this feature as VLAN for layer 3


    #hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4
    hosts:          files dns  # fix nslookup works but ping not work