Master Linux Network Configuration: From IP Settings to NIC Bonding

Linux Network Settings 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‑interface-name   # show details of a specific NIC
ifconfig -a                         # show all interfaces, even down
ifconfig interface [up|down]        # enable or disable an interface
ifconfig interface ip/netmask      # set IP address and netmask
ifconfig interface ip[/mask‑len]    # temporary change
ifconfig ens33:0 address           # virtual interface

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 modify IP address

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

Best to restart the network service:

# systemctl restart network

3 Modify network card name

Temporary modify network card name

ip link set ens36 down   # bring the NIC down
ip link set ens36 name abc   # rename
ip link set abc up   # bring it back up

① down the interface ② rename ③ bring it up

[root@localhost ~]# ifconfig ens33 down

Socket error Event: 32 Error: 10053.

[root@localhost ~]# ip link set ens33 name mcb
[root@localhost ~]# ifconfig mcb up
[root@localhost ~]# ifconfig mcb
mcb: 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::761e:9150:7c6f:2b3d prefixlen 64 scopeid 0x20<link>
        ether 00:0c:29:96:50:48 txqueuelen 1000 (Ethernet)

4 Permanent modify network card name

# vim /etc/default/grub

reboot/init 6 succeeded

5 Practical: dual‑NIC configuration (experiment not finished)

① Add a NIC in the VM

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
...

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
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT qlen 1000

ip addr – network layer

[root@localhost ~]# ip addr
# shorthand: ip a
# add a new virtual IP
ip address add 172.19.8.211/16 dev ens33
# temporary IP
ip address add 10.0.0.88/24 dev ens33
# delete IP
ip address del 10.0.0.8/24 dev ens33

ip route – routing table

[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 Add route to 10.0.0.0/8 via 192.168.227.2

route add -net 10.0.0.0/8 gw 192.168.227.2

② Delete that route

route del -net 10.0.0.0/8

③ Add default route

route add -net 0.0.0.0(default) gw 192.168.227.2

④ Permanent route

# 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

When services are unreachable (e.g., ftp, httpd):

Ping to test connectivity and firewall.

Check service status: systemctl status <em>service</em> Use ss or netstat to view listening ports.

Verify service configuration files.

netstat options

-a show all connections, -n numeric output, -t TCP, -u UDP, -r routing table, -l listening, -p process info (requires root).

ss options

-t TCP, -u UDP, -w raw sockets, -x UNIX sockets, -l listening, -a all, -n numeric, -p program/PID, -e extended, -m memory, -o timers, -r resolve names.

Difference

ss works closer to the kernel and is faster; netstat is older and slower.

9 traceroute – trace packet path

Shows each hop the packet traverses to reach a destination IP.

10 nslookup – DNS query

Verifies that a DNS server can resolve domain names; alternatives include dig, host, ping.

11 Modify hostname

Temporary change

[root@localhost ~]# hostname mg

Changes disappear after reboot.

Permanent change

Method 1: command‑line editing of /etc/hostname (image omitted).

Method 2: edit /etc/sysconfig/network (image omitted).

12 tcpdump – packet capture

Powerful network protocol analyzer for capturing and displaying packets.

① Capture on a specific NIC

tcpdump -i ens33

② List available NICs

tcpdump -D

③ Capture packets for a specific host

tcpdump host 192.168.11.12

④ Capture packets with source/destination filters

# Capture ICMP from 192.168.12 to 192.168.11.9
tcpdump -i eth0 -nn icmp and src host 192.168.12 and dst host 192.168.11.9
# Capture TCP port 22 from 192.168.11.12
tcpdump tcp port 22 and src host 192.168.11.12
# Capture first 100 packets, exclude SSH port, source net 172.16.12.0/24
tcpdump tcp -i eth1 -t -s 0 -c 100 and dst port ! 22 and src net 172.16.12.0/24 -w ./target.cap

13 Bond multiple NICs

Bonding provides redundancy (active‑backup) or load‑balancing (dual‑master).

Steps

Add a second NIC in the VM.

Copy ifcfg-ens33 to ifcfg-ens36.

Create ifcfg-bond0 and configure slave interfaces.

Restart network and verify bond status.

# Stop firewall and SELinux
systemctl stop firewalld
setenforce 0
# Copy configuration
cd /etc/sysconfig/network-scripts
cp ifcfg-ens33 ifcfg-bond0
vim ifcfg-bond0   # configure MODE=active-backup, IP, etc.
# Add slaves
nmcli con add type bond-slave ifname ens33 master bond0
nmcli con add type bond-slave ifname ens36 master bond0
# Bring up slaves then bond
nmcli con up bond-slave-ens33
nmcli con up bond-slave-ens36
nmcli con up bond0

14 View bond0 status