Ping Test Cellular Modems

Overview

When performing ICMP ping tests over cellular networks, IPv6 is recommended over IPv4 due to how mobile carriers handle network address translation.

The Problem: CGNAT Blocks IPv4 ICMP

CGNAT (Carrier-Grade NAT) is a technique used by mobile carriers to conserve IPv4 addresses. Instead of assigning each device a unique public IPv4 address, the carrier places thousands of customers behind a single shared public IP.

┌─────────────────┐      ┌─────────────────┐      ┌─────────────────┐
│   Your Modem    │      │   Carrier NAT   │      │    Internet     │
│                 │      │                 │      │                 │
│  192.0.0.2      │─────►│  92.184.x.x     │─────►│   8.8.8.8       │
│  (private IP)   │      │  (shared IP)    │      │   (Google DNS)  │
└─────────────────┘      └─────────────────┘      └─────────────────┘

Why IPv4 ICMP Fails

Protocol	Port-based?	NAT Tracking	Result
TCP (HTTP)	Yes	Easy - uses ports	Works
UDP (DNS)	Yes	Easy - uses ports	Works
ICMP (Ping)	No	Difficult - no ports	Often blocked

ICMP packets don't have port numbers, making it difficult for the NAT gateway to route replies back to the correct customer. Many carriers simply block ICMP or don't properly route the replies.

Symptoms:

ping 8.8.8.8 returns 100% packet loss
curl http://example.com works fine
Modem shows "connected" but ping fails

The Solution: Use IPv6

Why IPv6 Works

With IPv6, your modem receives a globally routable public address - no NAT required.

┌─────────────────┐                              ┌─────────────────┐
│   Your Modem    │                              │    Internet     │
│                 │◄────────────────────────────►│                 │
│  2a01:cb06:...  │      Direct connection       │  2001:4860:...  │
│  (public IP)    │      No NAT translation      │  (Google DNS)   │
└─────────────────┘                              └─────────────────┘

Aspect	IPv4 + CGNAT	IPv6
Address type	Private (192.0.0.x)	Public (2a01:...)
NAT required	Yes	No
ICMP routing	Problematic	Direct
Ping reliability	Often fails	Works reliably

Proof

# IPv4 ping - FAILS (CGNAT blocks ICMP)
$ ping -I wwan0 8.8.8.8

PING 8.8.8.8 (8.8.8.8) from 192.0.0.2 wwan0: 56(84) bytes of data.
--- 8.8.8.8 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss

# IPv6 ping - WORKS (direct public address)
$ ping -I wwan0 2001:4860:4860::8888

PING 2001:4860:4860::8888 from 2a01:cb06:... wwan0: 56 data bytes

64 bytes from 2001:4860:4860::8888: icmp_seq=1 ttl=113 time=45.9 ms

64 bytes from 2001:4860:4860::8888: icmp_seq=2 ttl=113 time=31.9 ms
--- 2001:4860:4860::8888 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss

Recommended Ping Targets

IPv6 (Recommended)

Target	Address	Provider
Google DNS (primary)	`2001:4860:4860::8888`	Google
Google DNS (secondary)	`2001:4860:4860::8844`	Google
Cloudflare DNS (primary)	`2606:4700:4700::1111`	Cloudflare
Cloudflare DNS (secondary)	`2606:4700:4700::1001`	Cloudflare

IPv4 (May fail on CGNAT)

Target	Address	Provider
Google DNS (primary)	`8.8.8.8`	Google
Google DNS (secondary)	`8.8.4.4`	Google
Cloudflare DNS (primary)	`1.1.1.1`	Cloudflare
Cloudflare DNS (secondary)	`1.0.0.1`	Cloudflare

Troubleshooting

Check Your IP Version

# Check assigned IPs on modem interface
ip addr show wwan0

# Example output:
# inet 192.0.0.2/27        <- IPv4 (private, behind CGNAT)
# inet6 2a01:cb06:.../64   <- IPv6 (public, no NAT)

Verify IPv6 Connectivity

# Test IPv6 ping
ping6 2001:4860:4860::8888

# Test IPv6 HTTP
curl -6 http://ifconfig.me

Common Issues

Issue	Cause	Solution
IPv4 ping fails, IPv6 works	CGNAT blocking ICMP	Use IPv6 targets
Both fail	No signal / not registered	Check `mmcli -m 0` status
IPv6 not available	Carrier doesn't support	Fall back to TCP-based tests

Summary

Recommendation	Reason
Use IPv6 for ping tests	Avoids CGNAT ICMP blocking
Default to `2001:4860:4860::8888`	Reliable, widely available

For network performance testing over cellular connections, always prefer IPv6 to ensure reliable ICMP ping measurements.