Virtual servers receive all the client connections and distribute them among the servers. A virtual server has an IP address, a port, and a protocol. For Layer 4 virtual servers, lists of ports ranges can be specified instead of a single TCP or UDP port to support complex protocols with dynamic ports.

A Layer 4 virtual server must be associated to a primary server pool, also called a default pool.

If a virtual server status is disabled, any new connection attempts to the virtual server are rejected by sending either a TCP RST for the TCP connection or ICMP error message for UDP. New connections are rejected even if there are matching persistence entries for them. Active connections continue to be processed. If a virtual server is deleted or disassociated from a load balancer, then active connections to that virtual server fail.



  1. With admin privileges, log in to NSX Manager.
  2. Select Networking > Load Balancing > Virtual Servers > Add.
  3. Enter a name and a description for the Layer 4 virtual server.
  4. Select a Layer 4 protocol from the drop-down menu.
    Layer 4 virtual servers support either the Fast TCP or Fast UDP protocol, but not both. For Fast TCP or Fast UDP protocol support on the same IP address and port, for example DNS, a virtual server must be created for each protocol.
    Based on the protocol type, the existing application profile is automatically populated.
  5. Toggle the Access Log button to enable logging for the Layer 4 virtual server.
  6. Click Next.
  7. Enter the virtual server IP address and port number.
    You can enter the virtual server port number or port range.
  8. Complete the advanced properties details.
    Option Description
    Maximum Concurrent Connection Set the maximum concurrent connection allowed to a virtual server so that the virtual server does not deplete resources of other applications hosted on the same load balancer.
    Maximum New Connection Rate Set the maximum new connection to a server pool member so that a virtual server does not deplete resources.
    Default Pool Member Port Enter a default pool member port if the pool member port for a virtual server is not defined.

    For example, if a virtual server is defined with port range 2000-2999 and the default pool member port range is set as 8000-8999, then an incoming client connection to the virtual server port 2500 is sent to a pool member with a destination port set to 8500.

  9. Select an existing server pool from the drop-down menu.
    The server pool consists of one or more servers, also called pool members that are similarly configured and running the same application.
  10. Select an existing sorry server pool from the drop-down menu.
    The sorry server pool serves the request when a load balancer cannot select a backend server to the serve the request from the default pool.
  11. Click Next.
  12. Select the existing persistence profile from the drop-down menu.
    Persistence profile can be enabled on a virtual server to allow related client connections to be sent to the same server.
  13. Click Finish.