Linux Network Fundamentals

Seven-layer OSI and four-layer TCP/IP reference models:

　　

Application layer: The highest level, provides the interface service between the network and the user should the software, such as HTTP,FTP,SMTP,POP3

Presentation layer: Responsible for data format transformation, encryption, compression, recovery, etc.

Session layer: Used to organize communication between two session processes

Transport Layer: Provides end-to-end service; tcp/udp

Network layer: Select the best path for grouping via subnet via routing algorithm

Data Link Layer:

Physical layer: The lowest level, using physical transport media to provide physical connectivity to the data link layer

Application layer:

Transport Layer:

Interconnect Layer:

Host-Network layer

IP Address: IPv4 mainstream

IPV6 Trends

Class A: 1.0.0.0-126.255.255.255

Class B: 128.0.0.0-191.255.255.255

Class C: 192.0.0.0-223.255.255.255

Special Address 10.0.0.0-10.255.255.255

127.0.0.1

172.16.0.0-172.31.255.255

192.168.0.0-192.168.255.255

　　　　　　　　　　

[[email protected]/]# IPCALC-BMN 192.168.1.3/24 COMPUTE subnet mask, broadcast, and network number

netmask=255.255.255.0

broadcast=192.168.1.255

network=192.168.1.0

[[email protected]/]# route-n View routing information

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

172.16.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1

169.254.0.0 0.0.0.0 255.255.0.0 U 1002 0 0 eth0

169.254.0.0 0.0.0.0 255.255.0.0 U 1003 0 0 eth1

0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

Add a route, destination network segment; 211.220.1.0/24 all data is sent through the gateway 192.168.1.1 and passed through the eth0 NIC

[Email protected]/]# Route add-net 211.220.1.0 netmask 255.255.255.0 gw 192.168.1.1 Dev eth0

[Email protected]/]# route-n

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

211.220.1.0 192.168.1.1 255.255.255.0 UG 0 0 0 eth0

172.16.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1

169.254.0.0 0.0.0.0 255.255.0.0 U 1002 0 0 eth0

169.254.0.0 0.0.0.0 255.255.0.0 U 1003 0 0 eth1

0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

[Email protected]/]# Route del-net 211.220.1.0/24 GW 192.168.1.1 Dev eth0

Delete

[[email protected]/]# ifconfig-View Network Device interface information

Eth0 Link encap:ethernet HWaddr 00:0c:29:a0:9b:d5

inet addr:192.168.1.3 bcast:192.168.1.255 mask:255.255.255.0

Inet6 ADDR:FE80::20C:29FF:FEA0:9BD5/64 Scope:link

Up broadcast RUNNING multicast mtu:1500 metric:1

RX packets:27697 errors:0 dropped:0 overruns:0 frame:0

TX packets:8761 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:2020334 (1.9 MiB) TX bytes:2538083 (2.4 MiB)

Interrupt:19 Base address:0x2000

eth1 Link encap:ethernet HWaddr 00:0c:29:a0:9b:df

inet addr:172.16.100.1 bcast:172.16.255.255 mask:255.255.0.0

Inet6 ADDR:FE80::20C:29FF:FEA0:9BDF/64 Scope:link

Up broadcast RUNNING multicast mtu:1500 metric:1

RX packets:81 errors:0 dropped:0 overruns:0 frame:0

TX packets:18 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:15030 (14.6 KiB) TX bytes:1324 (1.2 KiB)

Interrupt:16 Base address:0x2080

Lo Link encap:local Loopback

inet addr:127.0.0.1 mask:255.0.0.0

Inet6 addr::: 1/128 scope:host

Up LOOPBACK RUNNING mtu:65536 metric:1

RX packets:1568 errors:0 dropped:0 overruns:0 frame:0

TX packets:1568 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:0

RX bytes:89656 (87.5 KiB) TX bytes:89656 (87.5 KiB)

Set up a sub-interface of a NIC and activate

[Email protected]/]# ifconfig eth0:0 192.168.1.4 netmask 255.255.255.0 up

[Email protected]/]# ifconfig-a

Eth0 Link encap:ethernet HWaddr 00:0c:29:a0:9b:d5

inet addr:192.168.1.3 bcast:192.168.1.255 mask:255.255.255.0

Inet6 ADDR:FE80::20C:29FF:FEA0:9BD5/64 Scope:link

Up broadcast RUNNING multicast mtu:1500 metric:1

RX packets:27971 errors:0 dropped:0 overruns:0 frame:0

TX packets:8892 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:2043236 (1.9 MiB) TX bytes:2550985 (2.4 MiB)

Interrupt:19 Base address:0x2000

eth0:0 Link encap:ethernet HWaddr 00:0c:29:a0:9b:d5

inet addr:192.168.1.4 bcast:192.168.1.255 mask:255.255.255.0

Up broadcast RUNNING multicast mtu:1500 metric:1

Interrupt:19 Base address:0x2000

You can set the network configuration with the Setup command:

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To view the configuration file:

[Email protected]/]# cd/etc/sysconfig/network-scripts

[[email protected] network-scripts]# ls

Ifcfg-eth0 ifdown ifdown-ib ifdown-isdn ifdown-routes ifup ifup-eth Ifup-ipv6 ifup-plusb Ifup-rou TES ifup-wireless Network-functions

Ifcfg-eth1 IFDOWN-BNEP ifdown-ippp ifdown-post ifdown-sit ifup-aliases ifup-ib ifup-isdn ifup-post ifup-sit Init.ipv6-global Network-functions-ipv6

Ifcfg-lo ifdown-eth Ifdown-ipv6 ifdown-ppp ifdown-tunnel ifup-bnep ifup-ippp ifup-plip ifup-ppp Ifup-tun Nel net.hotplug

[[email protected] network-scripts]# cat Ifcfg-eth0 Nic 1

Device=eth0

Type=ethernet

Uuid=d1680cf6-689c-4126-9c78-635e28957da6

Onboot=yes

Nm_controlled=yes

Bootproto=none

Hwaddr=00:0c:29:a0:9b:d5

Defroute=yes

Peerroutes=yes

Ipv4_failure_fatal=yes

Ipv6init=yes

Name= "System eth0"

ipaddr=192.168.1.3

netmask=255.255.255.0

gateway=192.168.1.1

Userctl=no

[[email protected] network-scripts]# cat ifcfg-eth1 Nic 2

Ce=eth1

Type=ethernet

Onboot=yes

Nm_controlled=yes

Bootproto=none

Hwaddr=00:0c:29:a0:9b:df

Defroute=yes

Peerroutes=yes

Ipv4_failure_fatal=yes

Ipv6init=yes

Name= "System eth1"

ipaddr=172.16.100.1

netmask=255.255.0.0

Device=eth1

Userctl=no

[Email protected] network-scripts]#

Netstat: An explanation of usage

-A: Show all protocol and socket connection information

-N: Corresponding source IP and destination IP address

-L: Displays information being monitored

-T:TCP protocol

-U:UDP protocol

-P: Server name

[Email protected] network-scripts]# Netstat-antulp

Active Internet connections (servers and established)

Proto recv-q send-q Local address Foreign address State Pid/program Name

TCP 0 0 0.0.0.0:21 0.0.0.0:* LISTEN 1878/vsftpd

TCP 0 0 0.0.0.0:53 0.0.0.0:* LISTEN 1833/dnsmasq

TCP 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1855/sshd

TCP 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 1632/cupsd

TCP 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 2276/master

TCP 0 0 127.0.0.1:6010 0.0.0.0:* LISTEN 3687/sshd

TCP 0 0 0.0.0.0:50831 0.0.0.0:* LISTEN 1593/rpc.statd

TCP 0 0 0.0.0.0:111 0.0.0.0:* LISTEN 1469/rpcbind

TCP 0 192.168.1.3:22 192.168.1.2:4682 established 3687/sshd

TCP 0 0::: +:::* LISTEN 1833/DNSMASQ

TCP 0 0::: $:::* LISTEN 1855/sshd

TCP 0 0:: 1:631:::* LISTEN 1632/CUPSD

TCP 0 0::: 3128:::* LISTEN 2351/(squid)

Nslookup:domain name | IP Address

/etc/sysconfig/network: Used to set host name and whether the NIC is loaded when system starts

/etc/service: A network Service configuration file for converting the network service name to a port number/protocol;

Linux Network Fundamentals