Using TCG120-4 and TCG140-4 with IPv6 allows the devices to communicate through mobile networks that provide IPv6 connectivity. Both controllers support mobile data connections over IPv4 and IPv6, and the required IP version can be selected from the System page of the device.
When the device is configured to use IPv6, it is important to make sure that the remote servers and services configured in the device are also accessible over IPv6. An IPv6 mobile connection may be established successfully while an individual service still cannot reach its remote server — this does not necessarily indicate a malfunction of the TCG120-4, TCG140-4, or their cellular modem.
Key takeaways
- TCG120-4 and TCG140-4 support both IPv4 and IPv6 mobile connections, selectable on the System page.
- A working IPv6 mobile connection does not guarantee that every configured remote service is reachable.
- Check the DNS record (AAAA), then IPv6 reachability, then the actual service port — in that order.
- Servers configured with an IPv4-only address may become unreachable once the device runs in IPv6-only mode.
Step 1
Check whether you use an IP address or a hostname
Review the remote addresses configured for services such as HTTP/HTTPS, monitoring, email, or other external connections. A hostname does not indicate by itself whether the corresponding server supports IPv4, IPv6, or both — that depends on its DNS records. When using an IPv6-only connection, we recommend using remote services that provide IPv6 connectivity.
| Address type | Example | What it tells you |
|---|---|---|
| IPv4 address | 212.25.45.120 | Fixed address — carries no information about IPv6 support |
| IPv6 address | 2001:db8:1234::10 | Already IPv6 — ready to use as configured |
| Hostname | server.example.com | Depends on DNS — continue to Step 2 |
Step 2
Check whether a hostname supports IPv6
If a service is configured using a hostname, check whether it has an IPv6 DNS record. The DNS record used for an IPv6 address is called an AAAA record. If an AAAA record is returned, the hostname has an IPv6 address published in DNS — for example: server.example.com. AAAA 2001:db8:1234::10. If only an A record is available, the server is published only with an IPv4 address.
www.google.com has an AAAA record; www.teracomsystems.com does not.This check only confirms that an IPv6 address has been published in DNS. It does not mean the computer used for testing has working IPv6 connectivity.
Step 3
Test the server over IPv6
Having an AAAA record does not necessarily mean the server itself is reachable. If your local network does not provide IPv6 connectivity, use an online tool such as DNSChecker, which sends ping requests from an IPv6-enabled remote server. Keep in mind that some servers and firewalls block ping requests — an unsuccessful ping does not always mean the service is unavailable, so testing the actual port (Step 4) is more reliable.
Step 4
Check the actual service port
A successful IPv6 ping alone is not enough — the server may respond to ICMP while the required service port stays unavailable. An HTTPS service, for example, must accept IPv6 connections on TCP port 443. Whenever possible, test the actual protocol and port used by the TCG120-4 or TCG140-4, not only ping.
| Check | Windows | Linux / macOS |
|---|---|---|
| AAAA DNS record | nslookup -type=AAAA server.example.com | dig AAAA server.example.com |
| IPv6 reachability | ping -6 server.example.com | ping -6 server.example.com |
| HTTPS / port test | curl -6 https://server.example.com | curl -6 https://server.example.com |
No local IPv6 connectivity? Use an online curl tool instead. A result of HTTP/2 200 confirms the hostname resolved to an IPv6 address, the connection to port 443 succeeded, and the server responded correctly.
Step 5
Be careful with IPv4-only destinations
A server configured directly with an IPv4 address (for example 212.25.45.120) should not be assumed reachable when the TCG120-4 or TCG140-4 is operating with an IPv6-only mobile connection. Some mobile networks provide IPv4/IPv6 translation, others don’t — behavior can depend on the mobile operator and APN configuration. For reliable operation, make sure every remote server the device needs is directly accessible over IPv6 when using IPv6-only mode.
Quick checklist
Before switching the TCG120-4 or TCG140-4 to IPv6 only, check:
- All required remote servers support IPv6
- Hostnames have valid AAAA DNS records
- The servers can actually be reached over IPv6
- The required service ports are accessible over IPv6
- Firewall rules allow IPv6 traffic
- No required service depends exclusively on an IPv4 address
Important
A successful IPv6 mobile connection and accessibility of a remote server are two different things. The TCG120-4 or TCG140-4 may be correctly registered on the mobile network with a working IPv6 data connection while an IPv4-only remote service remains unreachable. If a service stops working after switching to IPv6-only mode, verify the IPv6 accessibility of the configured remote server before troubleshooting the cellular module.
FAQ
What is an AAAA record and why does it matter?
An AAAA record is the DNS record type that publishes a hostname’s IPv6 address, the same way an A record publishes an IPv4 address. Checking for an AAAA record is the first step in confirming a hostname can be reached over IPv6.
My device has a working IPv6 mobile connection — why can’t it reach a service?
A working IPv6 mobile connection only confirms the device is registered on the network. It does not confirm that a specific remote server or service is reachable over IPv6. That has to be checked separately, per service.
Is a successful IPv6 ping enough to confirm a service works?
No. A server can respond to ping while the actual service port is unavailable, and some servers or firewalls block ping entirely. Testing the real protocol and port — for example with curl -6 on port 443 for HTTPS — is more reliable.
What happens if a remote server only has an IPv4 address?
It should not be assumed reachable in IPv6-only mode. Some mobile operators provide IPv4/IPv6 translation and others don’t, so behavior depends on the operator and APN configuration. Servers required by the device should be directly accessible over IPv6.
A service stopped working after switching to IPv6-only — what should I check first?
Verify the IPv6 accessibility of the configured remote server (DNS, ping, and port) before troubleshooting the cellular module itself. In most cases the mobile connection is working correctly and the issue is on the remote service side.
Need reliable cellular remote I/O?
See full specifications, MQTT and IPv6 support, and configuration details for the TCG120-4.
View TCG120-4 product pagePart of: Cellular remote monitoring