Networking: ifconfig vs ip

Old tutorials say ifconfig. Windows people type ipconfig. Modern Linux uses ip. Let's sort out all three, learn how a server finds its way to the internet, and then fix one that can't.

Networking in five minutes

                    INTERNET  (8.8.8.8, google.com, …)
                        │
               ┌────────┴────────┐
               │  router 192.168.1.1  ← the GATEWAY (the door out) + DHCP + DNS
               └────────┬────────┘
      ┌─────────────────┼──────────────────┐
  laptop             server               printer
  192.168.1.23       192.168.1.50         192.168.1.80
               (all in 192.168.1.0/24 — the same local network)

• IP address: a computer's address on the network, like 192.168.1.50.
• /24 (subnet): how much of the address is the “street name.” /24 means the first three numbers must match, so everything in 192.168.1.x can talk directly. Old tools write it as a netmask: 255.255.255.0.
• Gateway (default route): where to send anything not on your street. Usually the router, .1.
• DNS: the internet's phone book. It turns google.com into an IP address.
• DHCP: the router hands out addresses automatically. The opposite is a static address you set yourself (servers often want one).
• 127.0.0.1 / lo: “loopback,” meaning this computer talking to itself.
• MAC address: the network card's built-in hardware ID, like 08:00:27:4c:1a:7e.

Old tools, new tools, Windows tools

For decades Linux used the net-tools package: ifconfig, route, netstat, arp. It stopped being developed around 2011 and was replaced by iproute2: the ip and ss commands. Today neither family installs net-tools by default, so ifconfig just says “command not found.”

sudo dnf install net-tools     # if you really want ifconfig
rpm -qf $(which ip)            # ip comes from "iproute"

sudo apt install net-tools     # if you really want ifconfig
dpkg -S $(which ip)            # ip comes from "iproute2"

Reading ip a (and ifconfig)

ip a

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 …                    ← loopback (this computer)
    inet 127.0.0.1/8 scope host lo
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 … state UP  ← card name, and it's UP
    link/ether 08:00:27:4c:1a:7e brd ff:ff:ff:ff:ff:ff           ← MAC address
    inet 192.168.1.50/24 brd 192.168.1.255 scope global dynamic enp0s3   ← IP + subnet; "dynamic" = from DHCP

The same card in old ifconfig style says inet 192.168.1.50 netmask 255.255.255.0: same information, different format. One real advantage of ip is that a card can have several addresses, and ifconfig only shows the first one.

Why the odd name enp0s3? Modern Linux names network cards after their physical slot (ethernet, pci bus 0, slot 3), so the names don't shuffle around when you reboot. Older systems and many cloud servers use eth0. Always check yours with ip -br link.

ip -br a         # brief: one line per card
ip route         # "default via 192.168.1.1" ← that's your gateway
ip neigh         # who's nearby on the LAN (the ARP table)

Where does it break? The troubleshooting ladder

When “the internet doesn't work,” climb this ladder from the bottom. The first step that fails is your problem:

Learn to recognize the error messages:

• Network is unreachable: there's no route to that address. Usually the default gateway is missing.
• Destination Host Unreachable: nobody on your LAN answers at that address.
• Temporary failure in name resolution: DNS problem.
• 100% packet loss with no other message: the host is down, or a firewall is ignoring you.

DNS: two very different setups

Before asking DNS, Linux checks /etc/hosts, a simple list of names and addresses that you can edit. Then it asks the DNS servers. How those are set up differs a lot between the families:

cat /etc/resolv.conf

# Generated by NetworkManager
nameserver 192.168.1.1

cat /etc/resolv.conf
resolvectl status

nameserver 127.0.0.53     ← a local helper, not the real server!
…
Current DNS Server: 192.168.1.1

dig google.com            # full DNS answer
dig +short google.com     # just the address
dig @1.1.1.1 google.com   # ask a specific DNS server
getent hosts google.com   # what programs actually see (hosts file first, then DNS)

One more difference: Ubuntu's /etc/hosts has a line 127.0.1.1 ubuntu for the machine's own name. Rocky's doesn't.

Changing the network: the big family difference

You can change things temporarily with ip. It's great for testing, but it's forgotten at reboot:

sudo ip addr add 192.168.1.99/24 dev enp0s3
sudo ip route add default via 192.168.1.1
sudo ip link set enp0s3 down      # careful over SSH!

For permanent settings, each family has its own system. Here's how to give the server a static address of .60:

nmcli                          # overview
nmcli con show                 # connection profiles
sudo nmcli con mod enp0s3 \
  ipv4.method manual \
  ipv4.addresses 192.168.1.60/24 \
  ipv4.gateway 192.168.1.1 \
  ipv4.dns 1.1.1.1
sudo nmcli con up enp0s3       # apply it

sudo nano /etc/netplan/50-cloud-init.yaml

network:
  version: 2
  ethernets:
    enp0s3:
      dhcp4: false
      addresses:
        - 192.168.1.60/24
      routes:
        - to: default
          via: 192.168.1.1
      nameservers:
        addresses: [1.1.1.1]

sudo netplan try      # apply, auto-undo in 120 s unless you press Enter
sudo netplan apply    # apply for real

The computer's name

hostnamectl                             # name, OS, kernel
sudo hostnamectl set-hostname webserver # permanent rename

Try it 1: explore the network

Try it 2: “the server can't reach the internet” 🔌

A student set this server up by hand and made two mistakes. Climb the ladder, find both, and fix them permanently with the right tool for the family.

Quick check