Introduction

In the previous article, we learned how to reach out to remote servers using ping and trace the path of packets with traceroute. But what if ping google.com doesn’t work, and traceroute stops right at the first step?

That’s a clear sign that the problem is nearby: on your computer, in the network cable, or in your home router. Before calling tech support, let’s check our own local network.

Today we’ll study two tools that act as your computer’s “passport” and “address book” in the network: ipconfig (or ifconfig/ip a) and arp.

ipconfig / ifconfig — Your PC’s Network Passport 🛂

If your computer were a house, its network settings would be the postal address. Without the correct address, data packets won’t find their way.

What does it do?

Displays information about network connections: IP address, subnet mask, default gateway.

Usage

Windows:

ipconfig

Linux/macOS:

ip a

Key lines

   IPv4 Address . . . . . . : 192.168.1.10   <-- Your PC’s address
   Subnet Mask  . . . . . . : 255.255.255.0  <-- Your "street" boundaries
   Default Gateway . . . .  : 192.168.1.1    <-- Internet exit (router)

• IPv4 Address — your PC’s address in the network (usually 192.168...).
• Subnet Mask — defines who counts as “neighbors.”
• Default Gateway — your router’s IP. No gateway = no internet.

What to look for when problems occur?

• Address 169.254.x.x — APIPA: the PC didn’t get an IP from DHCP. Check cable, Wi-Fi, or restart the router.

• No gateway — the computer doesn’t know where to send packets.

• Ping the gateway:

  ping 192.168.1.1
  

  If no response — the problem is in the connection to the router.

👉 Conclusion: ipconfig/ifconfig answer the question: “Did my computer get the right address, and does it know where the internet exit is?”

arp — The Address Book for Neighbors 📖

The IP address is logical, but to transfer packets you need a physical one (MAC address). ARP maps them together.

Usage

arp -a

Example

Interface: 192.168.1.10 --- 0x1
  Internet Address      Physical Address      Type
  192.168.1.1           00-1a-2b-3c-4d-5e     dynamic   <-- Router

If the gateway’s IP (192.168.1.1) is in the ARP table with a MAC address — contact is established. If there’s no entry — the PC can’t “reach” even at the physical level.

👉 Conclusion: arp shows whether the computer “sees” its neighbors (and especially the router) at the hardware level.

Conclusion

Now you have the tools to diagnose problems in the last mile:

• Check address and gateway (ipconfig/ifconfig).
• Check physical visibility (arp).
• Ping the router.

If everything’s fine here, but ping google.com still doesn’t work, the issue lies in the next link — DNS.

What’s Next?

In the next article, we’ll dive into the world of DNS — the “phone book” of the internet — and learn to use nslookup and dig.

Resources

• ipconfig (Windows)
• ip (Linux)
• ARP basics (Wikipedia)