Help Center/ Elastic Load Balance/ User Guide/ User Guide for Shared Load Balancers/ Listener/ Adding a TCP Listener
Updated on 2025-07-25 GMT+08:00
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Adding a TCP Listener

Scenarios

You can add a TCP listener, if high reliability and high accuracy are required but slow speed is acceptable. TCP works well for applications such as file transfer, email sending and receiving, and remote login.

Constraints

If the front protocol is TCP, the backend protocol defaults to TCP 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 TCP listener

    Parameter

    Description

    Frontend Protocol

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

    Select TCP.

    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.

    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)

    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 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