Ping Fails After Updating A Record – Technical Diagnosis and Network-Level Analysis

📅 18 Feb 2026 📂 General 👁 0 views

This article provides a technical explanation and troubleshooting framework for scenarios where:

DNS A records resolve correctly
But ICMP ping fails (e.g., Destination Host Unreachable, Request Timed Out)

Intended audience:

IT professionals
System administrators
Network engineers
Support engineers

Focus areas:

DNS resolution vs network reachability
ICMP behavior
Firewall / cloud security rules
Practical diagnostics

System & Protocol Overview

DNS A Record

Maps a hostname → IPv4 address.

Example:

example.com → 20.244.86.69

DNS success only confirms name resolution, not service availability.

ICMP Ping

Ping uses ICMP Echo Request / Reply.

Important:

✔ Ping tests ICMP reachability
❌ Ping does NOT test HTTP/HTTPS availability

Modern servers frequently block ICMP.

Technical Behavior Explanation

After updating an A record:

Layered Flow

Layer	Function	Status in This Scenario
DNS	Name → IP resolution	✅ Working
Network Routing	Path to IP	❓ Depends
Firewall	ICMP filtering	❓ Common cause
Service Layer	HTTP/HTTPS/IIS/Apache	Independent

Key Insight

DNS Resolution Success ≠ Ping Success

Example:


ping 20.244.86.69 → Unreachable
http://example.com → Working

This is a valid and common configuration.

Common Root Causes

1️⃣ ICMP Blocked by Server Firewall (Most Common)

Linux Servers

Check firewall rules:


sudo iptables -L -n
sudo ufw status

Allow ICMP:


sudo ufw allow proto icmp

Windows Servers

Check firewall:


wf.msc

Enable rule:


File and Printer Sharing (Echo Request – ICMPv4-In)

2️⃣ Cloud Provider Security Rules

Cloud platforms often block ICMP by default.

Microsoft Azure

Check:

✔ Network Security Group (NSG)

Allow ICMP:


Inbound Rule:
Protocol: ICMP
Port: *
Action: Allow
Priority: <lower number>

AWS EC2

Security Group Rule:


Type: All ICMP
Source: 0.0.0.0/0 (or restricted IP)

Google Cloud

Firewall Rule:


Protocol: ICMP
Action: Allow

3️⃣ Upstream Network Filtering

Possible filtering at:

Data center edge firewall
ISP filtering
Corporate network security appliances

4️⃣ Routing / Connectivity Issues

Symptoms:

✔ DNS resolves
❌ Ping unreachable
❌ Services unavailable

Diagnostics:


tracert 20.244.86.69   (Windows)
traceroute 20.244.86.69 (Linux/macOS)

Diagnostic Workflow

Step 1 – Confirm DNS Resolution


nslookup example.com
dig example.com

Expected:


Name: example.com
Address: 20.244.86.69

Step 2 – Test ICMP


ping 20.244.86.69

Possible outputs:

Output	Interpretation
Reply from	ICMP allowed
Request timed out	ICMP blocked
Destination host unreachable	Routing/firewall issue

Step 3 – Test TCP Connectivity

Ping failure alone is insufficient.

Test HTTP:


telnet example.com 80
telnet example.com 443

Or:


curl -I http://example.com

Step 4 – Port-Level Validation


nmap example.com

Example result:


80/tcp open http
443/tcp open https

Even if ping fails → services may be operational.

Common Errors & Technical Interpretation

Error: Destination Host Unreachable

Possible Causes:

ICMP blocked
Routing failure
Firewall rejection

Verification:


traceroute IP

Error: Request Timed Out

Most Likely Cause:

✔ Silent ICMP drop by firewall

Error: Unknown Host

Root Cause:

❌ DNS resolution failure

Check:


nslookup domain

Security Considerations

Blocking ICMP is common for:

✔ Reducing network reconnaissance
✔ Preventing host discovery
✔ Mitigating scanning attacks

However:

❌ ICMP blocking may hinder diagnostics
❌ Can affect MTU/path discovery

Security Risks of Enabling Ping

Allowing ICMP:

Makes server detectable
Aids network mapping by attackers
May increase scanning exposure

When Ping Should Be Allowed

Recommended only if:

✔ Internal infrastructure
✔ Monitoring systems require ICMP
✔ Controlled environments

Best Practices

✔ Do NOT Use Ping as Website Health Indicator

Use:

HTTP monitoring
TCP checks
Application-level probes

✔ Use Multi-Layer Diagnostics

Always test:

✔ DNS → ✔ TCP → ✔ Service

✔ Validate From Multiple Networks

Eliminates:

ISP filtering
Local firewall issues

✔ Implement Proper Monitoring

Prefer:

HTTP(S) health checks
Synthetic monitoring
Port-based probes

Conclusion

A failed ping after updating an A record typically indicates:

✔ ICMP filtering
✔ Firewall/security configuration
✔ NOT a DNS problem

Correct validation approach:

Confirm DNS resolution
Test TCP/service availability
Diagnose firewall/network rules if required

Ping failure alone is not evidence of downtime.

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