diff --git a/README-zh.md b/README-zh.md
index 8620109..5137316 100644
--- a/README-zh.md
+++ b/README-zh.md
@@ -336,6 +336,7 @@ https://gitlab.com/hwdsl2/setup-ipsec-vpn/-/raw/master/extras/vpnupgrade.sh
 - [域名和更改服务器 IP](docs/advanced-usage-zh.md#域名和更改服务器-ip)
 - [仅限 IKEv2 的 VPN](docs/advanced-usage-zh.md#仅限-ikev2-的-vpn)
 - [VPN 内网 IP 和流量](docs/advanced-usage-zh.md#vpn-内网-ip-和流量)
+- [指定 VPN 服务器的公有 IP](docs/advanced-usage-zh.md#指定-vpn-服务器的公有-ip)
 - [自定义 VPN 子网](docs/advanced-usage-zh.md#自定义-vpn-子网)
 - [转发端口到 VPN 客户端](docs/advanced-usage-zh.md#转发端口到-vpn-客户端)
 - [VPN 分流](docs/advanced-usage-zh.md#vpn-分流)
diff --git a/README.md b/README.md
index dd92d30..66d140d 100644
--- a/README.md
+++ b/README.md
@@ -336,6 +336,7 @@ See [Advanced usage](docs/advanced-usage.md).
 - [DNS name and server IP changes](docs/advanced-usage.md#dns-name-and-server-ip-changes)
 - [IKEv2-only VPN](docs/advanced-usage.md#ikev2-only-vpn)
 - [Internal VPN IPs and traffic](docs/advanced-usage.md#internal-vpn-ips-and-traffic)
+- [Specify VPN server's public IP](docs/advanced-usage.md#specify-vpn-servers-public-ip)
 - [Customize VPN subnets](docs/advanced-usage.md#customize-vpn-subnets)
 - [Port forwarding to VPN clients](docs/advanced-usage.md#port-forwarding-to-vpn-clients)
 - [Split tunneling](docs/advanced-usage.md#split-tunneling)
diff --git a/docs/advanced-usage-zh.md b/docs/advanced-usage-zh.md
index 9c4abec..ed286ae 100644
--- a/docs/advanced-usage-zh.md
+++ b/docs/advanced-usage-zh.md
@@ -6,6 +6,7 @@
 * [域名和更改服务器 IP](#域名和更改服务器-ip)
 * [仅限 IKEv2 的 VPN](#仅限-ikev2-的-vpn)
 * [VPN 内网 IP 和流量](#vpn-内网-ip-和流量)
+* [指定 VPN 服务器的公有 IP](#指定-vpn-服务器的公有-ip)
 * [自定义 VPN 子网](#自定义-vpn-子网)
 * [转发端口到 VPN 客户端](#转发端口到-vpn-客户端)
 * [VPN 分流](#vpn-分流)
@@ -182,9 +183,36 @@ iptables -I FORWARD 4 -i ppp+ -d 192.168.43.0/24 -j DROP
 iptables -I FORWARD 5 -s 192.168.43.0/24 -o ppp+ -j DROP
 ```
 
+## 指定 VPN 服务器的公有 IP
+
+在具有多个公有 IP 地址的服务器上，高级用户可以使用变量 `VPN_PUBLIC_IP` 为 VPN 服务器指定一个公有 IP。例如，如果服务器的 IP 为 `192.0.2.1` 和 `192.0.2.2`，并且你想要 VPN 服务器使用 `192.0.2.2`：
+
+```
+sudo VPN_PUBLIC_IP=192.0.2.2 sh vpn.sh
+```
+
+请注意，如果在服务器上已经配置了 IKEv2，则此变量对 IKEv2 模式无效。在这种情况下，你可以移除 IKEv2 并使用自定义选项重新配置它。参见 [使用辅助脚本配置 IKEv2](ikev2-howto-zh.md#使用辅助脚本配置-ikev2)。
+
+如果你想要 VPN 客户端在 VPN 连接处于活动状态时使用指定的公有 IP 作为其 "出站 IP"，并且指定的 IP **不是** 服务器上的主 IP（或默认路由），则可能需要额外的配置。在这种情况下，你可能需要更改服务器上的 IPTables 规则。如果要在重启后继续有效，你可以将这些命令添加到 `/etc/rc.local`。
+
+继续上面的例子，如果你希望 "出站 IP" 为 `192.0.2.2`：
+
+```
+# 获取默认网络接口名称
+netif=$(ip -4 route list 0/0 | grep -m 1 -Po '(?<=dev )(\S+)')
+# 移除 MASQUERADE 规则
+iptables -t nat -D POSTROUTING -s 192.168.43.0/24 -o "$netif" -m policy --dir out --pol none -j MASQUERADE
+iptables -t nat -D POSTROUTING -s 192.168.42.0/24 -o "$netif" -j MASQUERADE
+# 添加 SNAT 规则
+iptables -t nat -I POSTROUTING -s 192.168.43.0/24 -o "$netif" -m policy --dir out --pol none -j SNAT --to 192.0.2.2
+iptables -t nat -I POSTROUTING -s 192.168.42.0/24 -o "$netif" -j SNAT --to 192.0.2.2
+```
+
+要检查一个已连接的 VPN 客户端的 "出站 IP"，你可以在该客户端上打开浏览器并到 [这里](https://www.ipchicken.com) 检测 IP 地址。
+
 ## 自定义 VPN 子网
 
-默认情况下，IPsec/L2TP VPN 客户端将使用内部 VPN 子网 `192.168.42.0/24`，而 IPsec/XAuth ("Cisco IPsec") 和 IKEv2 VPN 客户端将使用内部 VPN 子网 `192.168.43.0/24`。有关更多详细信息，请阅读上一节。
+默认情况下，IPsec/L2TP VPN 客户端将使用内部 VPN 子网 `192.168.42.0/24`，而 IPsec/XAuth ("Cisco IPsec") 和 IKEv2 VPN 客户端将使用内部 VPN 子网 `192.168.43.0/24`。有关更多详细信息，请参见 [VPN 内网 IP 和流量](#vpn-内网-ip-和流量)。
 
 对于大多数用例，没有必要也 **不建议** 自定义这些子网。但是，如果你的用例需要它，你可以在安装 VPN 时指定自定义子网。
 
diff --git a/docs/advanced-usage.md b/docs/advanced-usage.md
index 19e47a0..151aab0 100644
--- a/docs/advanced-usage.md
+++ b/docs/advanced-usage.md
@@ -6,6 +6,7 @@
 * [DNS name and server IP changes](#dns-name-and-server-ip-changes)
 * [IKEv2-only VPN](#ikev2-only-vpn)
 * [Internal VPN IPs and traffic](#internal-vpn-ips-and-traffic)
+* [Specify VPN server's public IP](#specify-vpn-servers-public-ip)
 * [Customize VPN subnets](#customize-vpn-subnets)
 * [Port forwarding to VPN clients](#port-forwarding-to-vpn-clients)
 * [Split tunneling](#split-tunneling)
@@ -182,9 +183,36 @@ iptables -I FORWARD 4 -i ppp+ -d 192.168.43.0/24 -j DROP
 iptables -I FORWARD 5 -s 192.168.43.0/24 -o ppp+ -j DROP
 ```
 
+## Specify VPN server's public IP
+
+On servers with multiple public IP addresses, advanced users can specify a public IP for the VPN server using variable `VPN_PUBLIC_IP`. For example, if the server has IPs `192.0.2.1` and `192.0.2.2`, and you want the VPN server to use `192.0.2.2`:
+
+```
+sudo VPN_PUBLIC_IP=192.0.2.2 sh vpn.sh
+```
+
+Note that this variable has no effect for IKEv2 mode, if IKEv2 is already set up on the server. In this case, you may remove IKEv2 and set it up again using custom options. Refer to [Set up IKEv2 using helper script](ikev2-howto.md#set-up-ikev2-using-helper-script).
+
+Additional configuration may be required if you want VPN clients to use the specified public IP as their "outgoing IP" when the VPN connection is active, and the specified IP is NOT the main IP (or default route) on the server. In this case, you may need to change IPTables rules on the server. To persist after reboot, you can add these commands to `/etc/rc.local`.
+
+Continuing with the example above, if you want the "outgoing IP" to be `192.0.2.2`:
+
+```
+# Get default network interface name
+netif=$(ip -4 route list 0/0 | grep -m 1 -Po '(?<=dev )(\S+)')
+# Remove MASQUERADE rules
+iptables -t nat -D POSTROUTING -s 192.168.43.0/24 -o "$netif" -m policy --dir out --pol none -j MASQUERADE
+iptables -t nat -D POSTROUTING -s 192.168.42.0/24 -o "$netif" -j MASQUERADE
+# Add SNAT rules
+iptables -t nat -I POSTROUTING -s 192.168.43.0/24 -o "$netif" -m policy --dir out --pol none -j SNAT --to 192.0.2.2
+iptables -t nat -I POSTROUTING -s 192.168.42.0/24 -o "$netif" -j SNAT --to 192.0.2.2
+```
+
+To check the "outgoing IP" for a connected VPN client, you may open a browser on the client and [look up the IP address on Google](https://www.google.com/search?q=my+ip).
+
 ## Customize VPN subnets
 
-By default, IPsec/L2TP VPN clients will use internal VPN subnet `192.168.42.0/24`, while IPsec/XAuth ("Cisco IPsec") and IKEv2 VPN clients will use internal VPN subnet `192.168.43.0/24`. For more details, read the previous section.
+By default, IPsec/L2TP VPN clients will use internal VPN subnet `192.168.42.0/24`, while IPsec/XAuth ("Cisco IPsec") and IKEv2 VPN clients will use internal VPN subnet `192.168.43.0/24`. For more details, see [Internal VPN IPs and traffic](#internal-vpn-ips-and-traffic).
 
 For most use cases, it is NOT necessary and NOT recommended to customize these subnets. If your use case requires it, however, you may specify custom subnet(s) when installing the VPN.