> For the complete documentation index, see [llms.txt](https://docs.up-network.ch/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.up-network.ch/documentation/en/guides/network-troubleshooting.md).

# Diagnose a network problem

Start by specifying what is failing: an IP address, DNS name, protocol or the entire service. Check the [infrastructure status](https://status.as213929.ch/) and your machine’s status in its management portal.

## Check the operating system

For a Linux server you can access, collect the addresses, routes and listening services:

```sh
ip -br address
ip -4 route show
ip -6 route show
ss -tulpen
```

Compare the addresses with the delivery settings. If the console works and SSH fails, check the SSH service and firewall before changing the network.

## Separate DNS and connectivity

Test the name with your DNS tool and compare its A/AAAA records with the expected destination. A difference between IPv4 and IPv6 may explain intermittent access depending on client networks.

A missing ping response does not alone prove an outage: ICMP may be filtered. Also test the relevant service’s port from your network and, if possible, a second network.

A traceroute or MTR test provides information about the path. Loss shown on an intermediate router that is not also seen at the destination is not, on its own, proof of application traffic loss.

For BGP or a tunnel, note the session status, received and announced routes, delivery location and confirmed MTU. Do not change the settings of all tunnels during diagnosis.

## Submit diagnostic information

In your [ticket](/documentation/en/guides/how-to-open-a-support-ticket.md), add the source and destination IP addresses, date with timezone, protocol, port, expected result and useful outputs. Specify whether the failure affects IPv4, IPv6 or both.

The [Looking Glass](https://looking.house/companies/up-network-ch/looking-glass) lets you compare a public path from the operator’s network.

Updated on 3 October 2026. References: [status](https://status.as213929.ch/), [network solutions](https://up-network.ch/services/network-solutions).