diff --git a/Known-issues-and-solutions.md b/Known-issues-and-solutions.md
index 146ba6a..0d04135 100644
--- a/Known-issues-and-solutions.md
+++ b/Known-issues-and-solutions.md
@@ -21,4 +21,14 @@ udp2raw -s -l${your_server_ip}:443 -r127.0.0.1:1234
 Otherwise sometimes there will be some subtle problems hard to debug.
 
 Related issue:
-https://github.com/wangyu-/udp2raw-tunnel/issues/389
\ No newline at end of file
+https://github.com/wangyu-/udp2raw-tunnel/issues/389
+
+### VPN over udp2raw, traffic loop
+Sometimes you might want to make VPN connections through udp2raw. For example you run your VPN client and udp2raw client on the same machine. 
+
+VPN client usually provides some way to let you route your traffics through the VPN connection, or you can do it manually by your self with `ip route` rules.  No matter how you route your traffics,  make sure don't let VPN hijack udp2raw's traffic.  Otherwise, suppose your VPN is running through udp2raw and your udp2raw traffic is hijacked back to VPN, there will be a traffic loop.
+
+Usually you can avoid traffic loop by adding a route exception, for example on linux:
+```
+ip route add ${exception_ip} via ${default_network_gateway}
+```