Basic network management knowledge of Linux operating system

Today's notes are mainly about the basic knowledge of Linux operating system.

Network Management

(1) Check network status

In Linux, ifconfig, route and netstat are often used to check the network status. They are .net-tools tools. Let me use them below.

Let me talk about ifconfig and route.

There are many network card interfaces in our Linux, such as eth0, the first network card network interface, eno1, the onboard network card, and ens33, the PCI-E network card. CentOS 7 uses consistent network device naming. If none of the above matches, eth0 is used.

 [root@node01 ~]# ifconfig eth0
 eth0: error fetching interface information: Device not found
 [root@node01 ~]# ifconfig ens33
 ens33: flags = 4163 < UP ,BROADCAST,RUNNING,MULTICAST > mtu 1500
        inet 192.168.92.90 netmask 255.255.255.0 broadcast 192.168.92.255
        inet6 fe80::b889:1772:c306:ef8f prefixlen 64 scopeid 0x20 < link >  
        ether 00:0c:29:07:43:5a txqueuelen 1000 (Ethernet)
        RX packets 910 bytes 954985 (932.6 KiB)
        RX errors 0 dropped 0 overruns 0 frame 0
        TX packets 450 bytes 38942 (38.0 KiB)
        TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

(2) Network configuration file

ifcfg-eth0, /etc/hosts

When configuring hadoop and elasticsearch clusters, you need to configure the cluster IP and host name in /etc/hosts. Sometimes you cannot ping Baidu, maybe the domain name cannot be resolved, you need to configure it in /etc/sysconfig/network-scripts/ifcfg-eth0

 [root@node01 ~]# vim /etc/sysconfig/network
 #########
 HOSTNAME = node01  
 [root@node01 ~]# vim /etc/hosts
 #########
 192.168.92.90 node01
 192.168.92.91 node02
 192.168.92.92 node03 
 
 [root@node01 ~]# Configure DNS, domain name resolution service
 [root@node01 ~]# vim /etc/sysconfig/network-scripts/ifcfg-eth0
 DNS1 = 202.106.0.20​
 DNS2 = 8.8.8.8​

(3) Troubleshooting commands

First, ping Baidu: Check whether the target machine's network is accessible

 maoli@ubuntu:~$ ping baidu.com
 PING baidu.com (220.181.38.148) 56(84) bytes of data.
 64 bytes from 220.181.38.148: icmp_seq = 1   ttl = 128   time = 49.6 ms
 64 bytes from 220.181.38.148: icmp_seq = 2   ttl = 128   time = 48.2 ms
 ^C
 --- baidu.com ping statistics ---
 2 packets transmitted, 2 received, 0% packet loss, time 1001ms
 rtt min/avg/max/ mdev = 48.223 /48.948/49.673/0.725 ms

traceroute

• nslookup: nslookup www.baidu.com Server is the IP address corresponding to the domain name

 maoli@ubuntu:~$ nslookup www.baidu.com
 Server: 127.0.1.1
 Address: 127.0.1.1#53 
 
 Non-authoritative answer:
 www.baidu.com canonical name = www.a.shifen.com .
 Name: www.a.shifen.com
 Address: 182.61.200.6
 Name: www.a.shifen.com
 Address: 182.61.200.7

• Telnet: If the IP is reachable, but the service still has problems, you can use telnet to check the service port status
• tcpdump: tcpdump -i any -n port 80 # Capture all network card (any) port 80 data packets and display them in ip format (-n)

 maoli@ubuntu:~$ sudo tcpdump -i any -n port 80 -n
 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
 listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
 10:28:11.003675 IP 192.168.92.1.53951 > 192.168.92.135.80: Flags [S], seq 185886164, win 64240, options [mss 1460,nop,wscale 8,nop,nop,sackOK], length 0
 10:28:11.003875 IP 192.168.92.135.80 > 192.168.92.1.53951: Flags [S.], seq 2863640054, ack 185886165, win 64240, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0
 10:28:11.004114 IP 192.168.92.1.53951 > 192.168.92.135.80: Flags [.], ack 1, win 4106, length 0
 10:28:11.010472 IP 192.168.92.1.53951 > 192.168.92.135.80: Flags [P.], seq 1:476, ack 1, win 4106, length 475: HTTP: GET /sqli-labs/ HTTP/1.1

• tcpdump -i any -n host 10.0.0.1 and port 80# Capture the data packets between port 80 of all network cards and 10.0.0.1, and display them in IP format
• netstat Check whether the service listening port status is correct -n Display IP address -t TCP protocol -p Display the process corresponding to the port -l TCP listening status (listen) -ntpl Check the port opening status

 maoli@ubuntu:~$ sudo netstat -ntlp
 Activate Internet connection (server only)
 Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
 tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1111/sshd
 tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 14200/cupsd
 tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 1148/mysqld
 tcp 0 0 127.0.0.1:6379 0.0.0.0:* LISTEN 1165/redis-server 1
 tcp 0 0 127.0.1.1:53 0.0.0.0:* LISTEN 1285/dnsmasq
 tcp6 0 0 :::22 :::* LISTEN 1111/sshd
 tcp6 0 0 ::1:631 :::* LISTEN 14200/cupsd
 tcp6 0 0 :::9000 :::* LISTEN 2234/docker-proxy
 tcp6 0 0 :::80 :::* LISTEN 1842/apache2

(4) Network service management

There are two types of network service management programs, SysV and systemd. Systemd has now basically replaced SysV's Init.

(5) Set static IP

When building any cluster, you need to set a static IP.

 [root@node01]# vim /etc/sysconfig/network-scripts/ifcfg-ens33 
 
 ################
 BOOTPROTO = static  
 ONBOOT = "yes"  
 # The gateway address depends on the system's network
 GATEWAY = 192.168.92.2​
 # Set the static ip
 IPADDR = 192.168.92.92​
 NETMASK = 255.255.255.0​
 # Configure DNS server
 DNS1 = 8.8.8.8​
 DNS2 = 8.8.4.4​