Adding a UDP Listener

Scenarios

You can add a UDP listener, if quick response is required but low reliability is acceptable. UDP listeners are suitable for scenarios such as video chat, gaming, and real-time financial news.

Constraints

• UDP listeners do not support fragmentation.
• The UDP listener port cannot be 4789.
• Any UDP packet larger than 1,500 bytes will be discarded. To avoid this, ensure that the MTU value of the network interface is not greater than 1,500 bytes and modify the configuration files of applications based on the MTU value.
• The backend protocol can be UDP or QUIC if the frontend protocol is UDP.
• If you only select the application load balancing type for your dedicated load balancer, you cannot add UDP listeners to this load balancer.
• When a UDP listener routes traffic to IP as backend servers in a UDP backend server group over a Direct Connect connection or VPN connection, the health check result may be unhealthy. In this case, submit a service ticket.

Procedure

1. Go to the load balancer list page.
2. On the displayed page, locate the load balancer and click its name.
3. On the Listeners tab, click Add Listener. Configure the parameters based on Table 1.

   Table 1 Parameters for configuring a UDP listener

   Parameter	Description
   Name	Specifies the listener name.
   Frontend Protocol	Specifies the protocol that will be used by the load balancer to receive requests from clients. Select UDP.
   Frontend Port	Specifies the port that will be used by the load balancer to receive requests from clients. The port number ranges from 1 to 65535.
   Access Control	Specifies how access to the listener is controlled. For details, see What Is Access Control? The following options are available: All IP addresses Blacklist Whitelist
   IP Address Group	Specifies the IP address group associated with a whitelist or blacklist. If there is no IP address group, create one first. For more information, see IP Address Group.
   Transfer Client IP Address	Specifies whether to transmit IP addresses of the clients to backend servers. This function is enabled for dedicated load balancers by default and cannot be disabled. If you add IP addresses as backend servers for a dedicated load balancer that has a UDP listener, the source IP addresses of the clients cannot be passed to these servers.
   Advanced Settings (Optional)
   Idle Timeout (s)	Specifies the length of time for a connection to keep alive, in seconds. If no request is received within this period, the load balancer closes the connection and establishes a new one with the client when the next request arrives. The idle timeout duration ranges from 10 to 4000.
   Tag	Adds tags to the listener. Each tag is a key-value pair, and the tag key is unique.
   Description	Provides supplementary information about the listener. You can enter a maximum of 255 characters.

4. Click Next: Configure Request Routing Policy.
   1. You are advised to select an existing backend server group.
   2. You can also select Create new to create a backend server group.
      1. Configure the backend server group based on Table 3.
      2. Click Next: Add Backend Server. Add backend servers and configure a health check for the backend server group.

         For details about how to add backend servers, see Backend Server Overview. For the parameters required for configuring a health check, see Table 4.

5. Click Next: Confirm.
6. Confirm the configurations and click Submit.