Add some troubleshooting steps

docs/troubleshooting.md

@@ -136,3 +136,56 @@ The new node ID will have be re-authorized on any networks, and the node's manag
 
 - Delete peers.d too
 - Start the service
+
+## Troubleshooting Connection Issues
+
+It can be a little tricky to figure out why something isn't working. We'll try to improve this. Unfortunately you need to use the [CLI](cli) to troubleshoot.
+
+It's a peer to peer system, so we might need to check 2 or more nodes to deduce where the problem is.
+
+Go through these steps and see [corporate firewalls](corporate-firewalls) and [Router Tips](routertips) for more explanation.
+
+### Peers List
+
+Check this command on both peers
+
+`zerotier-cli peers`
+
+If one device has many "RELAY" connections, it's having a hard time connecting to things.
+
+If the connections to the PLANETs are RELAY, the node is having a very hard time. UDP traffic may be blocked.
+
+### Status
+
+`zerotier-cli info` it eventually says "RELAY" instead of "ONLINE" if UDP traffic is blocked.
+
+### Checking for Symmetric NAT
+
+`zerotier-cli info -j`
+
+Look at the "listeningOn" and "surfaceAddresses". If the surfaceAddress list large is constantly growing for each node you `ping`, this node may be behind Symmetric NAT. Other devices will have a hard time connecting with it.
+See [corporate firewalls](corporate-firewalls) for more info on Symmetric NAT.
+
+Ideally there is 1 surface address for each listening address/port.
+
+For a simplified example, if your computer only has 1 network interface and IP address, `listeningOn` will look like this:
+
+```json
+"listeningOn": [
+    "192.168.100.193/9993",
+    "192.168.100.193/55957",
+    "192.168.100.193/30431"
+    ]
+```
+
+then the `surfaceAddresses` should have only 3 entries
+
+```json
+"surfaceAddresses": [
+    "198.51.100.9/24/9993",
+    "198.51.100.9/30431",
+    "198.51.100.9/2785"
+   ],
+```
+
+Usually there is more going on in these entries and it can be hard to read. The output of `zerotier-cli dump` contains this information. If you send it to us, we can read it for you.