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

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

• DNS A records resolve correctly

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• 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

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:

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:

1. Confirm DNS resolution

2. Test TCP/service availability

3. Diagnose firewall/network rules if required

Ping failure alone is not evidence of downtime.