diff --git a/id-relay-set.md b/id-relay-set.md
index ab895a3..8c018a0 100644
--- a/id-relay-set.md
+++ b/id-relay-set.md
@@ -23,7 +23,7 @@ They are built on Centos7, tested on Centos7/8, Ubuntu 18/20.
 
 Run hbbs/hbbr on your server (Centos or Ubuntu). We suggust you use [pm2](https://pm2.keymetrics.io/) managing your service.
 
-By default, hbbs listens on 21115(tcp) and 21116(tcp/udp), hbbr listens on 21117(tcp).
+By default, hbbs listens on 21115(tcp) and 21116(tcp/udp), hbbr listens on 21117(tcp). Be sure to open these ports in the firewall.
 
 - TCP(21115, 21116, 21117)
 - UDP(21116)