[v16] docs: vnet troubleshooting for IP range conflicts

Backport #50516 to branch/v16
gravitational · Jan 17, 2025 · 53d4b2e · 53d4b2e
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diff --git a/docs/cspell.json b/docs/cspell.json
@@ -38,6 +38,7 @@
     "Brosnan",
     "CAcreateserial",
     "CCDC",
+    "CGNAT",
     "CHANGEID",
     "CHANGEME",
     "CLOUDSDK",
@@ -237,6 +238,7 @@
     "TOTP",
     "TOUCHID",
     "TSPN",
+    "Tailscale",
     "Tatham",
     "Tele",
     "Templating",

diff --git a/docs/pages/connect-your-client/vnet.mdx b/docs/pages/connect-your-client/vnet.mdx
@@ -65,6 +65,20 @@ $ tsh vnet
 
 ## Troubleshooting
 
+### Conflicting IPv4 ranges
+
+On the client computer, VNet uses IPv4 addresses from the CGNAT IP range `100.64.0.0/10` by
+default, and needs to configure addresses and routes for this range.
+This can conflict with other VPN-like applications, notably Tailscale also uses
+this range.
+
+If you are experiencing connectivity problems with VNet, check if you are
+running Tailscale or another VPN client, and try disabling it to see if the
+issue persists.
+To avoid the conflict and run VNet alongside Tailscale or another VPN client you
+can configure VNet to use a different IPv4 range, see our VNet configuration
+[guide](../enroll-resources/application-access/guides/vnet.mdx#configuring-ipv4-cidr-range).
+
 ### Connecting to the app without VNet
 
 Sometimes connectivity issues are not related to VNet, and you can narrow that down by trying to
@@ -131,4 +145,6 @@ client you use.
 
 ## Next steps
 
+- Read our VNet configuration [guide](../enroll-resources/application-access/guides/vnet.mdx)
+  to learn how to configure VNet access to your applications.
 - Read [RFD 163](https://github.com/gravitational/teleport/blob/master/rfd/0163-vnet.md) to learn how VNet works on a technical level.
diff --git a/docs/pages/enroll-resources/application-access/guides/vnet.mdx b/docs/pages/enroll-resources/application-access/guides/vnet.mdx
@@ -167,4 +167,6 @@ used depends solely on the app itself and its clients.
 
 ### Further reading
 
+- Read our VNet usage [guide](../../../connect-your-client/vnet.mdx) for end-users
+  accessing your applications with VNet.
 - Read [RFD 163](https://github.com/gravitational/teleport/blob/master/rfd/0163-vnet.md) to learn how VNet works on a technical level.