Checking IP settings on Windows, Linux and macOS

The four settings every PC needs

• An IP address in the right subnet
• The subnet mask (or prefix length)
• A default gateway: the router on its own subnet
• A DNS server, to turn names into addresses

Windows

ipconfig for the basics, ipconfig /all for everything: MAC address ("Physical Address"), whether DHCP is on, the DHCP server and lease times, and DNS servers.

In NetLab

▶ PC1
NetLab Windows-style command prompt. Type help to see the commands.
C:\Users\student>ipconfig /all

Windows IP Configuration

   Host Name . . . . . . . . . . . . : PC1
   Primary Dns Suffix  . . . . . . . : 
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . : 
   Description . . . . . . . . . . . : NetLab Gigabit Network Adapter
   Physical Address. . . . . . . . . : 00-1A-33-D5-62-B1
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::11db:99de:fbce:36d1%12(Preferred) 
   IPv4 Address. . . . . . . . . . . : 10.1.1.11(Preferred) 
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 10.1.1.1
   DNS Servers . . . . . . . . . . . : 

Linux

ip addr (address, prefix, MAC on the link/ether line), ip route (the default via line is the gateway), and the DNS server is in /etc/resolv.conf.

In NetLab

▶ PC2
student@PC2:~$ ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:1a:f2:3a:a4:ee brd ff:ff:ff:ff:ff:ff
    inet 10.1.1.12/24 brd 10.1.1.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::21a:f2ff:fe3a:a4ee/64 scope link 
       valid_lft forever preferred_lft forever
student@PC2:~$ ip route
default via 10.1.1.1 dev eth0 
10.1.1.0/24 dev eth0 proto kernel scope link src 10.1.1.12 

macOS

ifconfig en0 (the mask is shown in hex: 0xffffff00 = 255.255.255.0), netstat -rn for the gateway, and ipconfig getifaddr en0 for just the address.

In NetLab

▶ PC3
PC3:~ student$ ifconfig en0
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	ether 00:1a:dd:6c:93:9f
	inet6 fe80::d8e3:54d0:f8c5:988d%en0 prefixlen 64 secured scopeid 0x4 
	inet 10.1.1.13 netmask 0xffffff00 broadcast 10.1.1.255
	media: autoselect (100baseT <full-duplex>)
	status: active
PC3:~ student$ netstat -rn
Routing tables

Internet:
Destination        Gateway            Flags           Netif Expire
default            10.1.1.1           UGScg           en0
10.1.1.0/24        link#4             UCS             en0
PC3:~ student$ ipconfig getifaddr en0
10.1.1.13

Tip: In NetLab the IP settings button on any PC opens the same kind of dialog you'd use on a real desktop. Either way, always check the result with the commands above.