Tag: how ping works

The ping command is a powerful tool used in Linux to check network connectivity and diagnose issues. In this guide, we’ll explain how ping works and when to use it.

Learn the real technical power of the ping command with ICMP packet analysis, TTL insights, and real-world use cases for DevOps engineers.

What is ping?

The ping command is a powerful network diagnostic tool that tests reachability, latency, and packet loss between your machine and a remote host. It sends ICMP Echo Request packets and waits for ICMP Echo Replies.

Used by network admins, DevOps engineers, and cybersecurity professionals, ping helps quickly identify whether a host is up, how long it takes to respond, and if packets are being filtered or dropped

What Happens Internally When You Use ping

When you run:

ping google.com

1. DNS Resolution

Before sending packets, your machine resolves google.com to an IP using DNS.

dig google.com

2. ICMP Echo Request Packet is Creation

• Uses ICMP (Internet Control Message Protocol)
• Operates at Layer 3 (Network Layer)
• Uses raw sockets (SOCK_RAW with IPPROTO_ICMP)
• The kernel prepares an IP header + ICMP header + payload.

sudo tcpdump -i eth0 icmp

3. Packet Sent Through Network Stack

• Ethernet frame is created.
• Packet travels from your NIC → router → internet.

Deep Analysis of Ping Output

Explanation:

• icmp_seq: Sequence number of packets
• ttl: Time to Live – how many hops left
• time: Round-trip time

Understanding TTL and Hops

Each router reduces the TTL by 1. If it hits 0, the packet will dropped.

traceroute google.com

Useful for identifying bottlenecks in a route.

What Can Break the Ping Command?

If ping fails, it’s usually due to one of these reasons:

Reason	Symptom	Fix
DNS failure	ping: unknown host	Use dig, fix /etc/resolv.conf
ICMP blocked	Request timeout	Check firewall on both ends
Routing issue	No replies	Use traceroute, ip route

Advanced Ping Use Cases

1. Limit Number of Pings

ping -c 5 example.com

2. Custom Time Interval

ping -i 2 google.com

3. Check Internal Network

ping 192.168.1.1

4. Large Packet Test

ping -s 1024 google.com

Real-World Use Cases

• Check if server is alive
• Measure network latency
• Detect ICMP filtering by firewalls
• Test DNS resolution and routing issues

Pro Tips

• Use ping 8.8.8.8 to test direct IP-level connectivity.
• Use ping -t 1 to manually set TTL (test router hop limits).
• Use ping -f to flood-ping a host (admin use only).

Ping vs Traceroute vs Curl

Tool	Protocol	Purpose
ping	ICMP	Check if host is reachable
traceroute	ICMP/UDP	Path of packet
curl	TCP/HTTP	Application-level availability

Conclusion

The ping command isn’t just a beginner’s utility – it’s a powerful network-level diagnostic tool rooted in ICMP, IP routing, and system-level socket programming. Mastering it will instantly level up your ability to troubleshoot and diagnose network problems like a pro.

Next Steps

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