Octet

Say this first

ifconfig, route, arp and netstat come from net-tools, which talks to the kernel through old ioctl calls and /proc files and has barely changed in years. iproute2 (ip, ss, bridge, tc) uses netlink, the kernel's native networking interface, so it sees everything the kernel can do: several addresses per interface, multiple routing tables and policy rules, namespaces, VRFs and tunnels. Many minimal distros no longer install net-tools at all.

Go deeper

The mapping I use

Old (net-tools)	New (iproute2)
`ifconfig`	`ip addr` and `ip link`
`ifconfig eth0 up`	`ip link set eth0 up`
`route -n`	`ip route`
`arp -n`	`ip neigh`
`netstat -tulpn`	`ss -tulpn`
`netstat -i`	`ip -s link`
`brctl show`	`bridge link` or `ip link show master br0`
`vconfig add eth0 10`	`ip link add link eth0 name eth0.10 type vlan id 10`

What ifconfig gets wrong

It shows only the primary IPv4 address of an interface. A second address added with ip addr add is invisible to ifconfig unless it was given a label like eth0:1. People have chased "missing" addresses for hours because of this.
route -n shows only the main table. If policy routing is in use, it hides the tables that matter.
It knows nothing about namespaces, VRFs or most modern tunnel types.

Habits worth showing

Shell

ip -br addr        # one line per interface: name, state, addresses
ip -br link        # one line per interface: name, state, MAC, flags
ip -c route        # colour output
ip -s link show ens192   # packet, error and drop counters

They will ask next

Do changes made with ip survive a reboot?
No. ip changes the running kernel state only. To persist, put the config where the distro's network manager reads it: netplan YAML on Ubuntu, NetworkManager connections (nmcli) on RHEL family, .network files for systemd-networkd, or /etc/network/interfaces on classic Debian.
Is ifconfig removed from Linux?
No, it is a userspace package (net-tools) that is deprecated and often not installed by default. You can install it, but scripts and troubleshooting should use iproute2.

Traps

Saying ifconfig shows all addresses. It hides secondary addresses that have no label.
Forgetting that ip changes are runtime only and vanish on reboot or on a network service restart.

How did you do?