Network basics and Linux network configuration one Detailed explanation of ifconfig, route, netstat commands

OSI model and TCP/IP protocol cluster

1. First of all, TCP/IP is a protocol cluster; OSI (Open Systems Interconnection) is a model, and TCP/IP was developed before OSI.
2. TCP/IP is a hierarchical protocol made of some interactive modules, where each module provides specific functions; OSI specifies which function belongs to which layer.
3. TCP/IP is a five-layer structure, while OSI is a seven-layer structure.

4.TCP/IP is the currently used protocol, while OSI is used for learning

When computers transmit data, they need to use MAC addresses and IP network addresses for transmission. The IP address is only used to identify the network, and the MAC address is still used for actual transmission.

IP address:

IPv4: 32bits binary number.
8bits.8bits.8bits.8bits
Range: 0.0.0.0-255.255.255.255
Network ID:
0 000 0000 - 0 111 1111: 1-127
Number of networks: 126, 127
Number of hosts in each network: 2^24-2
Default subnet mask: 255.0.0.0,/8
​​Class B ：
The first two The segment is the network number, and the last two segments are the host number
Network number:
10 00 0000 - 10 11 1111: 128-191
Number of networks: 2^14
Number of hosts in each network: 2^16-2
Default Subnet mask: 255.255.0.0,/16 1:192-223
Number of networks: 2 ^21
Number of hosts in each network: 2^8-2
Default subnet mask: 255.255.255.0, /24
Class D: Multicast
1110 0000 - 1110 1111: 224-239
Class E: Scientific research
240-255

Class A: 1.0.0.0~126.255.255.255, default subnet mask/8, which is 255.0.0.0
(where 127.0.0.0~127.255.255.255 is the loopback address, used for local loopback testing etc.);
Private network address: 10.0.0.0~10.255.255.255;
Class B: 128.0.0.0~191.255.255.255, default subnet mask/16, which is 255.255.0.0;
Private network address: 172.16. 0.0~172.31.0.0;

Category C: 192.0.0.0~223.255.255.255, default subnet mask/24, which is 255.255.255.0;
Private network address 192.168.0.0~192.168.255.255

Category D: 224.0. 0.0~239.255.255.255, generally used for multicast

Class E: 240.0.0.0~255.255.255.255 (255.255.255.255 is the whole network broadcast address)
Class E addresses are generally used for scientific research





Place L inux Host access to the network



IP/NETMASK: local communication

Routing (gateway): cross-network communication

DNS server address: host name-based communication

Primary DNS server address

Alternate DNS server address

Chapter Three backup DNS server addresses

Configuration methods:

Static assignment

Dynamic allocation (DHCP)

Modify the configuration file (will not take effect immediately, can be permanent)

command modification (only this Valid once, invalid after restart)

Static allocation:

ifcfg family:

ifconfig: configure IP, NETMASK

route: route

netstat: status and statistics view

iproute2 family:

ip OBJECT:

addr: address and mask;

link: interface

route: routing

ss: status and statistics view

CentOS 7: nm (Network Manager) family

nmcli: command Line tool

nmtui: text window tool

ifcfg family details:

ifconfig:

Use the ifconfig command to view the network card information

[root@bogon ~]# ifconfig [eth0] #可省略

Configure the ip address information of the network card

[root@bogon ~]# ifconfig eth0:0 192.168.1.199/24

Then use the ifconifg command to view it, and you can see the information of the two network cards, respectively: eth0 and eth0:0. If you want to add more IPs, then the network card names will be: eth0:1, eth0:2...fill in as many as you want. OK!

Modify the network card MAC address

[root@bogon ~]# ifconfig eth0 hw ether 00:11:22:33:44:55

At this time, the hardware address of the network card has been changed. At this time, you can deceive the IP address bonding in the LAN.

Disable the network card

[root@bogon ~]# ifconfig eth0 down

Enable the network card

[root@bogon ~]# ifconfig eth0 up

route command

Function

route The command is used to view and configure the linux kernel routing table, which is used to View and configure Linux static routing tables.

Description

route command operation is based on the Linux kernel routing table. Its main function is to create a static route to allow a specified host or network to pass through a network interface, such as eth0. When the "add" or "del" parameter is used, the routing table is modified. If there are no parameters, the current contents of the routing table are displayed.

Command format

route command format is as follows:

route [-nee]
route add [-net|-host] [网络或主机] netmask [mask] [gw|dev]
route del [-net|-host] [网络或主机] netmask [mask] [gw|dev]

Parameter description

-n: #In the output routing information, directly display the IP address without displaying the host name, like the netstat command also has this parameter ;

-ee: #Display more detailed static routing information;

Add a new route (add) and delete a route (del) Related parameters of the route:

-net: #Destination address Is a network;

-host: #The target address is a host;

netmask: #When adding a network route, you need to use a network mask to determine the size of the network domain;

gw: #Abbreviation of gateway, route The gateway through which the data packet passes is followed by the IP address, which is different from dev;

dev: # If you just want to specify which network card goes out, use this setting, followed by the name of the network card device such as eth0;

Route viewing and management

[root@bogon ~]# route -n #查看
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     1002   0        0 eth0
0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 eth0

Meaning of routing table fields                                                                                                                   Destination network or destination host. time, only Shows the IP address, otherwise the hostname).

Gateway Gateway

The gateway address or ‘*’ if none set. Gateway address, if not, an asterisk will be displayed (0.0.0.0 when adding the -n option).

Genmask Netmask

The netmask for the destination net; ‘255.255.255.255’ for a host destination and ‘0.0.0.0’ for the default route. That is, “255.255.255.255″ represents a host. "0.0.0.0" represents the gateway.

Flags Possible flags include flags, commonly used ones are U and G.

U (route is up) route enabled

H (target is a host) target is a host

G (use gateway) use gateway

R (reinstate route for dynamic routing)

D (dynamically installed by daemon or redirect)

M (modified from routing daemon or redirect)

A (installed by addrconf)

C (cache entry)

! (reject route)

Metric distance, hop count. Not useful yet.

The ‘distance’ to the target (usually counted in hops). It is not used by recent kernels, but may be needed by routing dae-mons.

Ref Don’t worry, it will always be 0. Number of references to this route. (Not used in the Linux ker-nel.)

Use The number of times this route has been used can provide a rough estimate of the network traffic leading to the specified network address.

Count of lookups for the route. Depending on the use of -F and-C this will be either route cache misses (-F) or hits (-C).

Iface interface, i.e. eth0, eth0, etc. Network interface name Interface to which packets for this route will be sent.

Add route

[root@bogon ~]# route add -net 192.168.3.0/24 gw 192.168.1.1 dev eth0

Add a route to the 192.168.3.0 network, specify the network mask as 255.255.255.0 , the data packet passes through the network interface eth0, and the data packet will be sent to the gateway address 192.168.1.1

Add default route

[root@bogon ~]# route add  default  gw 192.168.1.1

Delete route

[root@bogon ~]# route add -net 192.168.3.0/24 gw 192.168.1.1 dev eth0

netstat command

is used to display various network related Information, such as network connections, routing tables, interface status (Interface Statistics), masquerade connections, multicast memberships (Multicast Memberships), etc.

Usage

netstat [-veenNcCF] [] -r

netstat {-V|--version|-h|--help}

netstat [-vnNcaeol] [ Netstat { [-veenNac] -I[] | [-veenNac] -i | [-cnNe] -M | -s } [delay]

Common parameters

-a (all)显示所有选项，默认不显示LISTEN相关
-t (tcp)仅显示tcp相关选项
-u (udp)仅显示udp相关选项
-n 拒绝显示别名，能显示数字的全部转化成数字。
-l 仅列出有在 Listen (监听) 的服务状态

-p 显示建立相关链接的程序名
-r 显示路由信息，路由表
-e 显示扩展信息，例如uid等
-s 按各个协议进行统计
-c 每隔一个固定时间，执行该netstat命令。

提示：LISTEN和LISTENING的状态只有用-a或者-l才能看到

常用组合

-tan, -uan, -tnl, -unl, -tunlp ...

列出处于监听状态的socket

[root@bogon ~]# netstat -l

显示所有被监听的tcp连接

[root@bogon ~]# netstat -tal
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address               Foreign Address             State      
tcp        0      0 *:ssh                       *:*                         LISTEN      
tcp        0      0 localhost:smtp              *:*                         LISTEN      
tcp        0     52 bogon:ssh                   bogon:6170                  ESTABLISHED 
tcp        0      0 *:ssh                       *:*                         LISTEN      
tcp        0      0 localhost:smtp              *:*                         LISTEN

显示所有接口的统计数据

[root@bogon ~]# netstat -i
Kernel Interface table
Iface       MTU Met    RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0       1500   0     3898      0      0      0     1828      0      0      0 BMRU
eth0:0     1500   0      - no statistics available -                            BMRU
lo        65536   0        0      0      0      0        0      0      0      0 LRU

   

  -I：指定接口的统计数据

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