[Linux] Basic Knowledge of Network

Basic Knowledge of Network
Even though If you are a server engineer, you need to have basic knowledge of Network. Let’s check important point of network in this article.
CentOS7 base command is described hear.
TCP (Transmission Control Protocol)
TCP is protocol to send/receive data by using IP (internet Protocol) scheme.
If data deficit or error is detected, the data will be sent again in TCP.UDP (User Datagram Protocol)
UDP does not check error or send data again.
Therefore UDP can send data faster than TCP.

How to Check IP address
1. ip a [address] [Interface]
IP address and subnet mask set to Network interface is displayed.

2. nmcli [Interface]
Interface for network setting by command line. Without any options, current network setting is displayed.

DNS setting file
1. /etc/nsswitch.conf
In this file,  designate what function is used for name resolving.
If you set “files” as primary, /etc/hosts file is used for name resolving.
If you set “dns” as primary, DNS server described in /etc/resolv.conf file is used for name resolving.

2. /etc/resolv.conf
IP address of DNS server is described in /etc/resolv.conf file.

Service check
1. ss command
Provided service name is displayed by ss command as below.
e.g.) Display list of TCP service.


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