# Troubleshoot TCP connection issues between two devices

Last validated Mar 16, 2026

If your devices are visible in the admin console, and there is no [access rule][kb-policy-syntax-access-rules] blocking connections between the devices, check the level of connectivity with Tailscale's three types of `ping`:

* `ping 100.x.x.x` tells the OS to send an ICMP ping across the tailnet.
* `tailscale ping 100.x.x.x` tests whether the two `tailscaled` processes can communicate at all, and how (direct, or relayed).
* `tailscale ping --tsmp 100.x.x.x` sends a packet that goes one level further than `tailscale ping`, also going through the WireGuard level, but doesn't involve the host's networking stack.

Packet size limits can also cause connection problems on certain types of networks.

Tailscale uses a maximum transmission unit (MTU) of `1280`. If there are other interfaces which might send a packet larger than this, those packets might get dropped silently. These can be verified by using `tcpdump`.

To solve this, we can set the MTU at the LAN level to a lower value, or use MSS (maximum segment size) clamping.

[kb-policy-syntax-access-rules]: /docs/reference/syntax/policy-file#access-rules