Can an MTU problem make a VPS connection partly work?
An MTU mismatch can allow small packets or an initial connection while larger traffic stalls. Tunnels add overhead and path-MTU discovery can be affected by filtering. Diagnose the path before changing the guest interface’s MTU.
Instructions
1. Describe the partial failure
Record whether SSH starts but hangs during output, HTTPS stalls on larger responses, or only a tunnel path is affected. These symptoms are suggestive, not conclusive; application or firewall problems can look similar.
2. Inspect the interface and path
Use an installed tracepath utility on Linux to gather a bounded route view.
ip link show
tracepath -n -m 10 198.51.100.20The destination is a documentation placeholder for an authorised peer. Review reported path MTU and the active interface’s MTU. Missing replies do not establish the cause by themselves.
3. Compare with the provider and tunnel design
Confirm the network’s supported MTU and any encapsulation overhead. Apply a reviewed change only to the intended interface or tunnel configuration, then verify small and larger application exchanges. Do not impose a blanket value across all interfaces.
Check the result
- The confirmed path and interface MTUs are compatible with the intended encapsulation.
- The actual application completes both small and larger transfers through the affected path.
Troubleshooting
- tracepath produces no useful responses
- Diagnostic probes may be filtered; use approved endpoint evidence and the provider’s network specification.
- Only the VPN path fails
- Check tunnel overhead, routing and permitted ICMP behaviour before changing the public interface.
Official references
Use the documentation for your installed version when a flag, service name or platform feature differs.