1-nmtui & nmcli commands.
The Nmcli and Nmtui commands are used to configure network settings and also to manage network devices for creating, editing, and deleting the network connections in Cent OS.
[root@localhost ~]# nmtui
//The above command will open a GUI for you to edit the network connections.
[root@localhost ~]# nmcli
eno2: connected to eno2
2-ARP Table
If you want to see the current ARP table of the system then you can run the below command given below.
Note:- ARP is a part of the net-tools package so you have to install it first.
[root@localhost /]# yum install net-tools
Once it will install the net-tool package then you can see the ARP table.
[root@localhost /]# arp -a
gateway (192.168.14.117) at b6:59:f3:be:24:6a [ether] on eno2
[root@localhost /]# arp -e
Address HWtype HWaddress Flags Mask Iface
gateway ether b6:59:f3:be:24:6a C eno2
[root@localhost /]#
3-Adding Gateway in Cent OS.
[root@localhost /]#route add default gw 192.168.14.117
4-Adding and Deleting Routes.
[root@localhost /]# route add -net 192.168.1.0/24 gw 192.168.14.117
[root@localhost /]# route del -net 192.168.1.0/24 gw 192.168.14.117
5-Viewing The Routing Table.
[root@localhost /]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default gateway 0.0.0.0 UG 100 0 0 eno2
192.168.14.117 0.0.0.0 255.255.255.252 U 100 0 0 eno2
[root@localhost /]#6-Nslookup Command.
nslookup command is also used to find out DNS information.The examples are given below for showing A Record (IP Address) of google.com.At first you have to install the bind utill package and then you can see the DNS resolution information.
[root@localhost /]#dnf install bind-utils -y
[root@localhost /]#nslookup www.google.com
7-DIG Command
Dig (domain information groper) query DNS-related information like “A” Record, CNAME, MX Record, etc. This command is mainly used to troubleshoot DNS-related queries.
[root@localhost /]# dig google.com
; <<>> DiG 9.11.13-RedHat-9.11.13-5.el8_2 <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11200
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;google.com. IN A
;; ANSWER SECTION:
google.com. 296 IN A 216.58.197.78
;; Query time: 3 msec
;; SERVER: 192.168.1.1#53(192.168.1.1)
;; WHEN: Sun Apr 04 14:27:11 EDT 2022
;; MSG SIZE rcvd: 558-Traceroute
traceroute is a network troubleshooting utility that shows the number of hops taken to reach a destination and also determines packets traveling path.At first, you have to install the traceroute package.
[root@localhost /]# yum install traceroute -y
Below Traceroute to facebook.com.
[root@localhost ~]# traceroute www.facebook.com
traceroute to www.facebook.com (157.240.239.35), 30 hops max, 60 byte packets
1 gateway (192.168.1.1) 0.185 ms 0.117 ms 0.146 ms
2 10.0.0.1 (10.0.0.1) 0.268 ms 0.229 ms 0.188 ms
3 13.0.0.1 (13.0.0.1) 69.342 ms 100.607 ms 100.480 ms
4 74.119.78.201 (74.119.78.201) 69.098 ms 69.008 ms po104.psw01.del1.tfbnw.net (31.13.25.169) 68.987 ms
5 157.240.39.97 (157.240.39.97) 69.365 ms 157.240.39.109 (157.240.39.109) 69.319 ms 173.252.67.229 (173.252.67.229) 68.980 ms
6 edge-star-mini-shv-02-del1.facebook.com (157.240.239.35) 68.928 ms 69.087 ms 68.982 ms
[root@localhost ~]# 9-Ping
Ping is the utility to test the reachability between source and destination.
–c is used for packet count, I select 10 because I want to send 10 ping packet to google.com
[root@localhost ~]# ping facebook.com
PING facebook.com (157.240.239.35) 56(84) bytes of data.
64 bytes from edge-star-mini-shv-02-del1.facebook.com (157.240.239.35): icmp_seq=1 ttl=59 time=69.4 ms
64 bytes from edge-star-mini-shv-02-del1.facebook.com (157.240.239.35): icmp_seq=2 ttl=59 time=69.0 ms
64 bytes from edge-star-mini-shv-02-del1.facebook.com (157.240.239.35): icmp_seq=3 ttl=59 time=68.8 ms
64 bytes from edge-star-mini-shv-02-del1.facebook.com (157.240.239.35): icmp_seq=4 ttl=59 time=68.9 ms
^C
--- facebook.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 68.864/69.055/69.406/0.338 ms
[root@localhost ~]#
[root@localhost ~]# ping -c 10 google.com
PING google.com (142.250.195.110) 56(84) bytes of data.
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=1 ttl=121 time=38.9 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=2 ttl=121 time=38.6 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=3 ttl=121 time=38.6 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=4 ttl=121 time=38.5 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=5 ttl=121 time=38.6 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=6 ttl=121 time=38.5 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=7 ttl=121 time=38.5 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=8 ttl=121 time=38.5 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=9 ttl=121 time=38.5 ms
64 bytes from maa03s39-in-f14.1e100.net (142.250.195.110): icmp_seq=10 ttl=121 time=38.5 ms
--- google.com ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 9015ms
rtt min/avg/max/mdev = 38.531/38.617/38.981/0.279 ms
[root@localhost ~]#
10-Enable or Disable Specific Interface
//Enable the port
[root@localhost ~]# ifup eth0
//Disable the port
[root@localhost ~]# ifdown eth0
11-MTU Size Configuration
The default MTU size is 1500 on Ethernet,But you can change it if you want, But it’s not recommended to change.
[root@localhost /]#ifconfig eth1 mtu 1500
12-Viewing the IP address on the port.
[root@localhost ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eno2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
link/ether 6c:de:4b:12:b3:12 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.2/30 brd 192.168.1.3 scope global noprefixroute eno2
valid_lft forever preferred_lft forever
[root@localhost ~]# ifconfig
eno2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.2 netmask 255.255.255.252 broadcast 192.168.1.3
ether 6c:de:4b:12:b3:12 txqueuelen 1000 (Ethernet)
RX packets 43020570 bytes 41675151184 (38.8 GiB)
RX errors 0 dropped 0 overruns 40 frame 0
TX packets 47428243 bytes 51462919413 (47.9 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device memory 0xc5a60000-c5a7ffff
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 28 bytes 2492 (2.4 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 28 bytes 2492 (2.4 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
[root@localhost ~]# 13-Configuring the Static IP address .
Create a file named /etc/sysconfig/network-scripts/ifcfg-eth2 as follows:
DEVICE=eth2
BOOTPROTO=none
ONBOOT=yes
PREFIX=24
IPADDR=192.168.1.2
Restart network service: systemctl restart network14-How to configure the IP through DHCP.
Create a file named /etc/sysconfig/network-scripts/ifcfg-eth2 as follows:
DEVICE="eth2"
ONBOOT=yes
NETBOOT=yes
UUID="41171a6f-bce1-44de-8a6e-cf5e782f8bd6"
IPV6INIT=yes
BOOTPROTO=dhcp
HWADDR="00:08:a2:0a:ba:b8"
TYPE=Ethernet
NAME="eth2"
Restart network service: systemctl restart network