Relay servers

TxHub always tries to connect your devices directly to each other. Sometimes that isn't possible, for example when both devices sit behind strict firewalls or carrier networks. Then traffic goes through a relay server instead, so the devices stay connected. Most TxNets never need to change anything here.

How it works#

• Each device measures how quickly it can reach each relay region and picks the fastest one as its home relay.
• When two devices start talking, the first packets may go through a relay while TxHub looks for a direct path. As soon as a direct path works, traffic switches to it.
• If no direct path can be found, traffic keeps going through the relay. The connection still works, but it is usually slower and has more delay, since every packet makes a detour.

Relays use HTTPS (TCP port 443), so they work on most networks that allow web browsing. Direct connections need outgoing UDP. If a network blocks UDP, devices on it are always relayed.

Your relay servers#

New TxNets start with TxHub's relay region in Iceland, named Iceland - TXHub (code ice), with two relay servers. Admins and owners can see and change the list under Settings → Relay servers.

The list is made of regions. A region is a group of relay servers in one place, and devices choose between regions by speed. Each region has a Region ID (a number), a short Code and a Name. Each relay server in a region (shown as a node) has these fields:

Add a region

1. Go to Settings → Relay servers.
2. Under Add Region, enter a Region ID, a Code and a Name, then click +. Use a Region ID that isn't already in the list.
3. In the new region, click Add node and fill in at least the Hostname. Add more nodes for redundancy.
4. Click Save at the top of the page. Connected devices get the new list within seconds.

To remove a region or a node, click its delete icon and then Save. A region can't be saved without at least one node, and every node needs a hostname.

See which relay a device uses#

In the dashboard, open a machine from Machines. Under Client Connectivity, Preferred relay server shows the Region ID of the device's home relay.

On the device itself, run:

$ txhub netcheck

The report shows, among other things:

• UDP: whether the device can send UDP. If it says false, direct connections aren't possible from this network and all traffic is relayed.
• IPv4 and IPv6: the public addresses the device was seen from.
• MappingVariesByDestIP: true means the network uses a strict type of NAT that makes direct connections harder.
• The nearest relay region, and how long it takes to reach each relay region.

Check if a connection is direct or relayed#

Run this on one of the two devices:

$ txhub status

Look at the last column for the other device:

100.64.0.7   desktop   alice@  linux    active; direct 203.0.113.25:41641, tx 52344 rx 81232
100.64.0.9   laptop    alice@  windows  active; relay "ice", tx 4120 rx 3880

The connection type only shows while the devices are talking. If you see idle or -, send some traffic first, for example with txhub ping laptop, and run txhub status again. A new connection often starts relayed and switches to direct after a few seconds.

Troubleshooting#

A connection stays relayed

Relayed connections work, so this is only a problem if they feel slow. To give direct connections a chance:

• Allow outgoing UDP on the firewall of at least one of the two networks.
• Run txhub netcheck on both devices. If one shows UDP: false, that network is the cause.
• Corporate, hotel and mobile networks often block direct connections. Try the same devices from another network to compare.

Devices can't reach each other at all

• Check that both devices are connected with txhub status.
• Check that your access policy allows the traffic. A relay doesn't bypass the access policy.
• If you changed Settings → Relay servers, check that each relay hostname resolves and that port 443 is reachable from the devices.

See also Troubleshooting.