View network configuration

Maximum mtu packet transfer rate

View network interface information ifconfig

• View all active network interface information
  • Execute ifconfig command
• View specified network interface information

ifconfig network interface

[root@localhost ~]# ifconfig ens33
ens33 flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.4.11 netmask 255.255.255.0 broadcast 192.168.4.255
inet6 fe80.9106:d38b:670d:1a89 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:3a:81:cc txqueuelen 1000(Ethernet)
..//Omit some contents

View host name hostname

• hostname command
  • View or set the current hostname

hostname[host name]((Provisional)

• Example

[root@localhost ~]# hostname
localhost.localdomain

View the route table entry route

route command

View or set routing table information in the host

route [-n]

Example

[root@localhost ~]# route -n
Kernel IP routing table
Destination     Gateway       Genmask      Flags    Metric    Ref    Use    lface
0.0.0.0       192.168.4.1     0.0.0.0       UG       100       0      0     ens33
192.168.4.0     0.0.0.0    255.255.255.0    U        100       0      0     ens33

View network connectivity netstat

• netstat command
  • View the network connection status, routing table, interface statistics and other information of the system

netstat [option]

• Common options
  • -a,-n,-p,-t,-u,-r

[root@localhost~]# netstat -anpt | grep ":80"
tcp60   0  :::80  :::*  LISTEN  20563/httpd

Get socket statistics ss

• ss command
  • Check the network connection of the system and obtain socket statistics

ss [option]

• Common options
  • -t,-u,-n,-l,-p,-a,-r

[root@localhost ~]# ss -t state established
Recv-Q  Send-Q   Local Address:Port   Peer Address:Port
0       96       192.168.8.10:ssh     192.168.8.1:55213

Test network connection

Test network connection ping

• ping command
  • Test network connectivity

ping[option]Target host

• Example

[root@localhost ~]# ping 192.168.4.110
PING 192.168.4.110 (192.168.4.110)56(84) bytes of data.
64 bytes from 192.168.4.110: icmp_seq=2 ttl=128 time=0.274 ms
^C  Press Ctrl+C abort test 
---192.168.4.110 ping statistics---
2 packets transmitted, 2 received,0% packet loss, time 1162ms
rtt min/avg/max/mdev = 0.274/0.484/0.694/0.210 ms

Trace packet traceroute

• traceroute command
  • Test the network nodes passing from the current host to the destination host

traceroute Destination host address

• Example

[root@localhost ~]# traceroute 192.168.7.7
traceroute to 192.168.7.7 (192.168.7.7),30 hops max, 40 byte packets
1 (192.168.4.1)7.740 ms 15.581 ms 15.881 ms
2 (192.168.7.7)19.652 ms 19.995 ms 19.942 ms

Domain name resolution nslookup

• nslookup command
  • Test DNS domain name resolution

nslookup Destination host address [DNS server address]

• Example

[root@localhost ~]# nslookup www.google.com
Server:  202.106.0.20     DNS server address
Address: 202.106.0.20#53
Non-authoritative answer:
Name: www.l.google.com    Analytic IP address
Address:173.194.127.51

Using the network configuration command

How to set network parameters

• Temporary configuration - use commands to adjust network parameters

  • It is simple and fast, and can directly modify the network parameters in operation
  • Generally, it is only suitable for use in the process of debugging the network
  • After the system is restarted, the modifications will be invalid

• Fixed settings - modify network parameters through the configuration file

  • Modify the configuration file of various network parameters
  • It is suitable for setting fixed parameters on the server
  • It will not take effect until the network service is overloaded or restarted

Set network interface parameter ifconfig

• Set the IP address and subnet mask of the network interface

ifconfig network interface ip address [netmask Subnet mask]
ifconfig network interface ip address [/Subnet mask length]

• Disable or reactivate the network card

ifconfig network interface up 
ifconfig network interface down

• Set virtual network interface

ifconfig network interface:Serial number IP address

Set route record

• The routing record added to the specified network segment

route add -net Network segment address gw IP address

• Delete the routing record to the specified network segment

route del -net Network segment address

• Adds a default gateway record to the routing table

route add default gw IP address

• Delete the default gateway record in the routing table

route del default gw IP address

Modify hostname hostname

• hostname command
  • Set host name

hostname Host name

Example

[root@localhost ~]# hostnamelocalhost.localdomain
[root@localhost ~]# hostname www.bdqncom
[root@localhost ~]# hostname
www.bdqn.com
[root@localhost ~]# bash enables a new Shell session
[root@www ~]#

Modify network profile

Network interface profile

• /Under / etc / sysconfig / network scripts /
  • ifcfg-ens33: configuration file of the first Ethernet card

[root@localhost ~]# ls /etc/sysconfig/network-scripts/ifcfg-*
/etc/sysconfig/network-scripts/ifcfg-ens33
/etc/sysconfig/network-scripts/ifcfg-lo

Network interface profile

• /Under / etc / sysconfig / network scripts /
  • ifcfg-ens33: configuration file of the first Ethernet card

[root@localhost ~]# vim /etc/sysconfig/network-scripts/ifcfg-ens33
TYPE=Ethernet
BOOTPROTO=static
DEVICE=ens33
ONBOOT=yes
IPADDR=192.168.4.11
NETMASK=255.255.255.0
GATEWAY=192.168.4.100

Enable and disable network interface configuration

• Restart network service

[root@localhost ~]# systemctl restart network

• Disable and enable network interface

[root@localhost ~]# ifdown ens33
[root@localhost ~]# ifup ens33

Domain name resolution profile

• /etc/resolv.conf file
  • Save the IP address of the DNS server that this machine needs to use

[root@localhost ~]# vi /etc/resolv.conf
search localdomain
nameserver 202.106.0.20
nameserver 202.106.148.1

Note: CentOS 7 needs to be installed in NetworkManager Set dns=none in the main section of the conf file and restart the NetworkManager service, or use the nmcti command newly added by CentOS7 to set it

Local host mapping file

• /etc/hosts file
  • Save the mapping record of host name and IP address

[root@localhost ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.
119.75.218.70 www.baidu.com

• Comparison between hosts file and DNS server
  • By default, the system first looks for the parsing record from the hosts file
  • The hosts file is only valid for the current host
  • The hosts file can reduce the DNS query process and speed up access

summary

• View network configuration
  • ifconfig,hostname,route,netstat,ss
• Test network connection
  • ping,traceroute,nslookup,dig
• Set network address parameters
  • Temporary configuration, permanent configuration