Master Linux Network Configuration: IP, Routes, Bonding and Diagnostic Tools

1. Configure Network Basics

Hostname : hostname command for temporary change; edit /etc/hostname or /etc/sysconfig/network for permanent change.

IP address / netmask : use ifconfig or ip a to view; ifconfig <iface> <IP> netmask <MASK> to set temporarily.

Default gateway : route -n or ip route.

DNS servers : view /etc/resolv.conf.

Network status : ss or netstat.

Domain lookup : nslookup, host, dig.

2. Using ifconfig

ifconfig                     # show all interfaces (including down)
ifconfig -a                  # show all interfaces, even inactive
ifconfig <iface> up|down    # enable or disable an interface
ifconfig <iface> <IP> netmask <MASK>   # set IP address
ifconfig <iface>:0 <IP>    # create virtual interface

Modify IP address

Example: ifconfig ens33 192.168.11.8 then verify with ifconfig. Restart the session (e.g., Xshell) if needed.

Add / Delete temporary IP

# add temporary IP
ip address add 10.0.0.88/24 dev ens33
# delete temporary IP
ip address del 10.0.0.8/24 dev ens33

3. Rename Network Interface Temporarily

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

4. Permanently Change IP Address

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

After editing, restart the network service: # systemctl restart network (or # systemctl restart NetworkManager on newer distros).

5. Permanent Interface Renaming

# vim /etc/sysconfig/network-scripts/ifcfg-ens33
# change NAME= and DEVICE= to the new name
# systemctl restart network

6. IP Management with ip

Link layer : ip link shows interfaces and their state.

Address layer : ip addr (or ip a) lists IPs; ip address add <IP/MASK> dev <iface> adds an address; ip address del <IP/MASK> dev <iface> removes it.

Routing : ip route displays routes; route add -net <net> gw <gw> adds a route; route del -net <net> deletes it; permanent routes can be saved in /etc/sysconfig/network-scripts/route-<iface> then restart network.

7. Network Diagnostics

ss / netstat

Common options: -t TCP, -u UDP, -a all, -n numeric, -p show process, -l listening sockets.

traceroute

Trace the path to a destination IP.

nslookup

Verify DNS resolution of hostnames.

tcpdump – packet capture

Capture on a specific interface: tcpdump -i ens33 List interfaces: tcpdump -D Filter by host, source, destination, port, protocol, etc. Example:

tcpdump -i eth0 -nn icmp and src host 192.168.12 and dst host 192.168.11.9
tcpdump port 1000
tcpdump tcp port 22 and src host 192.168.11.12

Limit capture size and count: -s 0 (full packet), -c 100 (stop after 100 packets), -w ./target.cap to save.

8. Bond (Link Aggregation) Configuration

Bonding combines multiple NICs for redundancy or load balancing.

Manual method (CentOS/RHEL)

# Copy existing config
cp /etc/sysconfig/network-scripts/ifcfg-ens33 /etc/sysconfig/network-scripts/ifcfg-ens36
# Edit ifcfg-ens36 (change NAME and DEVICE to ens36)
# Create bond0 config (ifcfg-bond0) with:
TYPE=Bond
BONDING_OPTS="mode=active-backup miimon=100"
DEVICE=bond0
ONBOOT=yes
IPADDR=192.168.91.123
NETMASK=255.255.255.0
GATEWAY=192.168.91.2
# Add slave interfaces to bond0
vim /etc/sysconfig/network-scripts/ifcfg-ens33   # set MASTER=bond0, SLAVE=yes
vim /etc/sysconfig/network-scripts/ifcfg-ens36   # same as above
# Restart network
systemctl restart network

Verify bond status with cat /proc/net/bonding/bond0 or ifconfig bond0.

NMCLI method (CentOS 8)

# Create static connection (no autoconnect)
nmcli con add con-name static ifname eth0 type ethernet ipv4.addresses 172.25.X.10/24 ipv4.gateway 172.25.X.254 autoconnect no
# Add bond 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 then bond
nmcli con up bond-slave-ens33
nmcli con up bond-slave-ens36
nmcli con up mybond0