Help Center/ Elastic Load Balance/ User Guide/ User Guide for Shared Load Balancers/ Listener/ Adding a UDP Listener
Updated on 2025-09-25 GMT+08:00
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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.
  • UDP listeners cannot use port 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.
  • If the listener protocol is UDP, the protocol of the backend server group is UDP by default and cannot be changed.

Procedure

  1. Go to the load balancer list page.
  2. On the displayed page, locate the load balancer and click its name.
  3. Under Listeners, click Add Listener. Configure the parameters based on Table 1.
    Table 1 Parameters for configuring a UDP listener

    Parameter

    Description

    Frontend Protocol

    Specifies the protocol that will be used by the load balancer to receive requests from clients.

    Select UDP.

    Listening 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.

    Name (Optional)

    Specifies the listener name.

    Transfer Client IP Address

    Specifies whether to allow the load balancer to communicate with backend servers using client IP addresses.

    For details, see Transfer Client IP Address.

    Access Control

    Specifies how access to the listener is controlled. For details, see What Is Access Control?

    All IP addresses is selected for access control by default.

    You can select Whitelist or Blacklist and choose an IP address group.
    • Whitelist: Only IP addresses in the whitelist can access the listener. Requests from the IP addresses or CIDR blocks specified in the IP address group will be forwarded by the listener.

      Access control policies only take effect for new connections, but not for existing ones. If a whitelist is configured for a listener but IP addresses that are not in the whitelist can access the backend server associated with the listener, it may be caused by a persistent connection between the client and the backend server. To deny IP addresses that are not in the whitelist from accessing the listener, the persistent connection between the client and the backend server needs to be disconnected.

    • Blacklist: IP addresses in the blacklist are not allowed to access the listener. Requests from the IP addresses or CIDR blocks specified in the IP address group will not be forwarded by the listener.

    More (Optional)

    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 2.
      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 3.

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