Master Linux Network Configuration: IP, Routing, Bonding and More

Linux Network Configuration and Basic Services

1 Configure Network Settings

Hostname: hostname

IP address/netmask: ifconfig; ip a

Default gateway: route -n

DNS server: cat /etc/resolv.conf

Network connection status: ss, netstat

Domain name resolution: nslookup, host

2 ifconfig

ifconfig          specific NIC name          # show detailed info for a specific NIC
ifconfig -a                           # show all NICs, including inactive ones
ifconfig NIC_NAME [up|down]           # enable or disable a NIC
ifconfig NIC_NAME ip_address/netmask  # set IP and netmask
ifconfig NIC_NAME ip_address/subnet_len # temporary change NIC name
ifconfig ens33:0 address               # virtual NIC

ifconfig modify IP address

inconfig ens33 new IP address

[root@localhost ~]# ifconfig ens33 192.168.11.8

[root@localhost ~]# ifconfig
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
        inet 192.168.11.8 netmask 255.255.255.0 broadcast 192.168.11.255
        inet6 fe80::42b7:9714:f504:2343 prefixlen 64 scopeid 0x20<link>
        ether 00:0c:29:96:50:48 txqueuelen 1000 (Ethernet)
        RX packets 641 bytes 49417 (48.2 KiB)

ifconfig add temporary IP address

ifconfig delete temporary IP address

Permanent IP address modification

# vim /etc/sysconfig/network-scripts/ifcfg-ens33

Best to restart the network service: # systemctl restart network

3 Modify Network Interface Name

Temporary rename

ip link set ens36 down
# first bring the NIC down
ip link set ens36 name abc
# then rename
ip link set abc up
# finally bring it up

Steps: ① down the interface ② rename ③ up the interface

4 Permanent rename

# vim /etc/default/grub

reboot/init 6 succeeded

5 Practical: Dual‑NIC Configuration (experiment not finished)

① Add a NIC in the virtual machine

② Copy ens33 configuration to ens36

[root@localhost ~]# cd /etc/sysconfig/network-scripts/
[root@localhost network-scripts]# cp ifcfg-ens33 ifcfg-ens36
[root@localhost network-scripts]# vim ifcfg-ens36

TYPE=Ethernet
BOOTPROTO=static
NAME=ens36
DEVICE=ens36
ONBOOT=yes
IPADDR=192.168.91.110
NETMASK=255.255.255.0
GATEWAY=192.168.91.2

[root@localhost network-scripts]# systemctl restart network

[root@localhost ~]# ping 192.168.11.20
PING 192.168.11.20 (192.168.11.20) 56(84) bytes of data.
64 bytes from 192.168.11.20: icmp_seq=1 ttl=64 time=0.058 ms
64 bytes from 192.168.11.20: icmp_seq=2 ttl=64 time=0.051 ms
64 bytes from 192.168.11.20: icmp_seq=3 ttl=64 time=0.050 ms
64 bytes from 192.168.11.20: icmp_seq=4 ttl=64 time=0.049 ms
64 bytes from 192.168.11.20: icmp_seq=5 ttl=64 time=0.048 ms

③ Modify ens36 configuration file

④ Test

6 IP

ip link – Data Link Layer

[root@localhost ~]# ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
    link/ether 00:0c:29:96:50:48 brd ff:ff:ff:ff:ff:ff
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT qlen 1000
    link/ether 52:54:00:8d:7b:87 brd ff:ff:ff:ff:ff:ff
4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN mode DEFAULT qlen 1000
    link/ether 52:54:00:8d:7b:87 brd ff:ff:ff:ff:ff:ff

ip addr – Network Layer

[root@localhost ~]# ip addr
# can be shortened to ip a
[ip address add 172.19.8.211/16 dev ens33]
# add a new virtual IP
[ip address add 10.0.0.88/24 dev ens33]   # temporary IP
[ip address del 10.0.0.8/24 dev ens33]

ip route – Routing

[root@localhost ~]# ip route
default via 192.168.11.2 dev ens33 proto static metric 100
192.168.11.0/24 dev ens33 proto kernel scope link src 192.168.11.20 metric 100
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1

route -n

7 Add/Delete Routes

Route fields meaning

Destination, Gateway, Genmask, Flags, Metric, Ref, Use, Iface

① route add -net 10.0.0.0/8 gw 192.168.227.2

Temporarily add a route to the 10.0.0.0 network via the specified gateway.

② route del -net 10.0.0.0/8

Delete the route to the 10.0.0.0 network.

③ route add -net 0.0.0.0 (default) gw 192.168.227.2

Add a default route.

④ Permanent route addition

# vim /etc/sysconfig/network-scripts/route-ens33
10.0.0.0/24 via 192.168.11.11
# systemctl restart network

8 ss / netstat – Network Connection Status

Service not working, ftp/httpd cannot be accessed
1. Ping to check connectivity and firewall status
2. systemctl status <service_name> to see if the service is running
3. ss or netstat to see if ports are occupied
4. Verify service configuration files

netstat

View network connections with options such as -a (all), -n (numeric), -t (TCP), -u (UDP), -r (routing), -l (listening), -p (process info, requires root).

ss

View network connections with options: -t (TCP), -u (UDP), -w (raw), -x (unix), -l (listening), -a (all), -n (numeric), -p (process), -e (extended), -m (memory), -o (timer), -r (resolve).

Difference

ss operates closer to the kernel and is faster; netstat is user‑level and slower.

9 traceroute – IP Path Tracing

Trace the route packets take to a destination.

10 nslookup

Domain name resolution; verifies DNS server functionality. Other tools include dig, host, ping.

11 Change Hostname

Temporary change

[root@localhost ~]# hostname mg

The change disappears after reboot.

Permanent change

① Command line

② Edit configuration file

12 tcpdump – Packet Capture

A powerful network protocol analyzer for monitoring and capturing traffic, widely used for troubleshooting, performance analysis, and security auditing.

① Capture on a specific NIC

② List available NICs

③ Capture specific host traffic

# tcpdump -i eth0
# tcpdump host 192.168.11.12
# tcpdump src host 192.168.11.12
# tcpdump dst host 192.168.11.12
# tcpdump tcp port 22 and src host 192.168.11.12
# tcpdump ip host 172.16.12.10 and 192.168.11.12
# tcpdump -i eth1 -t -s 0 -c 100 and dst port ! 22 and src net 172.16.12.0/24 -w ./target.cap
# tcpdump -c 1000

13 Bond Multi‑NIC Bonding

Provides redundancy (active‑backup) or load balancing (dual‑master) by binding multiple NICs to a single virtual interface.

① Add a NIC in the VM

② Switch to the configuration directory

③ Edit bond0 configuration

④ Modify ens33 and ens36

⑤ Restart network scripts

⑥ Test

# systemctl stop firewalld
setenforce 0
cd /etc/sysconfig/network-scripts
ifconfig
cp ifcfg-ens33 ifcfg-bondo
vim ifcfg-bond0
# (additional configuration steps)

14 View bond0 Status

Bonding method two (rarely used)

# centos8: nmcli bonding
nmcli con add con-name static ifname eth0 autoconnect no type Ethernet ipv4.addresses 172.25.X.10/24 ipv4.gateway 172.25.X.254
nmcli connection modify ens33 ipv4.addresses 192.168.91.100/2
nmcli connection up ens33
# add bonding interface
nmcli con add type bond con-name mybond0 ifname bond0 mode active-backup ipv4.method manual ipv4.addresses 192.168.91.123/24
# add slave interfaces
nmcli con add type bond-slave ifname ens33 master bond0
nmcli con add type bond-slave ifname ens36 master bond0
# bring up slaves and bond
nmcli con up bond-slave-ens33
nmcli con up bond-slave-ens36
nmcli con up mybond0