Network Management of Linux Learning articles

Port:

Number of ports: 0-2 ^ 16-1 (0-65535) → is limited by TCP and UDP protocol packet headers

FTP:20 21

SSH:22

Telnet:23

DNS:53

HTTP:80 → HTTPS:443

SMTP:25

POP3:110

Netstat-an # lists all current network connection status

-a: lists all connection states, including TCP/UDP/UNIX socket

-n: displays the IP address and port number instead of the hostname and service name

-t: only TCP packet connections are listed

-u: only UDP packet connections are listed

-p: lists the file names of PID and program

-l: lists only the network status of services that are already in Listen (listening)

-c: set to update automatically after a few seconds, for example,-c 5 updates the network status every 5 seconds

Netstat-tulnp # shows the network services that have been started

Netstat-atunp # View the status of all network connections on this computer

IP address configuration:

1) ifconfig command temporarily configure IP address

Ifconfig eth0 192.168.0.200 netmask 255.255.255.0

# temporarily set the IP address and subnet mask of the eth0 Nic

2) the setup tool permanently configures IP addresses

① setup

② vim / etc/sysconfig/network-scripts/ifcfg-eth0

# change ONBOOT=no to ONBOOT=yes

# in this way, the eth0 network card can be activated, otherwise the network card cannot be used

③ service network restart

3) modify the network configuration file

① vim / etc/sysconfig/network-scripts/ifcfg-eth0 # Nic information file (IP address, etc.)

② vim / etc/sysconfig/network # hostname file

Hostname hostname # View and temporarily set hostname

③ vim / etc/resolv.conf # DNS configuration file

4) Supplementary knowledge

Modify UUID:

① vim / etc/sysconfig/network-scripts/ifcfg-eth0

# Delete MAC address line

② rm-rf / etc/udev/rules.d/70-persistent-net.rules

# Delete Nic and MAC address binding file

③ restart the system

Network commands:

Ifconfig command

Ifdown network card device name: # disable the network card

Ifup network card device name: # enable the network card

Netstat-an | grep ESTABLISHED | wc-l # to see how many users are connecting to this server

Netstat-rn or route-n # View routes and gateways

Nslookup domain name # for domain name resolution

Ping

Telnet 192.168.0.252 80

Traceroute domain name or IP # route trace

Wget http://...... # download command

Tcpdump [- AennqX] [- I interface] [- w store file name] [- c times] [- r file] [packet data format to be extracted]

-A: the content of the packet is displayed in ASCII, which is usually used to capture WWW web page packet data.

-e: use MAC packet data from the data link layer (OSI layer 2) to display

-nn: directly displayed in IP and port number instead of hostname and service name

-Q: list only relatively short packet information

-X: the packet contents of hexadecimal (hex) and ASCII can be listed, which is useful for listening on packet contents.

-I: followed by the network port to be monitored, such as eth0,lo, etc.

-w: if you want to store the monitored packet data, use this parameter, followed by the file name

-r: read the packet data from the following file, which is made by-w

-c: if this parameter is not available, tcpdump will listen continuously

Example: tcpdump-I eth0-nn # obtains the data of eth0 network card with IP and port number

Tcpdump-I eth0-nn port 21 # only listens to port 21 data

Tcpdump-I eth0-nn-X 'port 21' # hexadecimal and ASCII view

Tcpdump-I eth0-nn 'port 22 and src host 192.168.1.101'

# snooping eth0, communication port 22, and destination packet source of 192.168.1.101

# it seems to be OK without quotation marks