The UDP fast path profile enables a virtual service to support UDP. NSX Advanced Load Balancer translates the client’s destination virtual service address to the destination server and writes the source IP address of the client to the address of the SE, when forwarding the packet to the server. This ensures that server response traffic traverses symmetrically through the original SE.

To create a UDP Fast Path network profile:


  1. In the New TCP/UDP Profile: screen, enter the Name of the network profile.
  2. Select UDP Fast Path as the Type.
  3. Enter the Direct Server Return details, if required.

    Configuring the DSR settings is optional.

  4. Click Enable DSR.
    1. Click the DSR Type (L2 or L3) to select the mode.
    2. Select IPinip as DSR Encapsulation Type.
  5. Enter the UDP Fast Path Settings as shown below:
    1. Enabling NAT Client IP Address (SNAT) performs source NAT for all client UDP packets.

      NAT Client IP Address (SNAT): By default, NSX Advanced Load Balancer translates the source IP address of the client to an IP address of the SE. This can be deactivated for connectionless protocols which do not require server response traffic to traverse back through the same SE. For example, a syslog server will silently accept packets without responding. Therefore, there is no need to ensure response packets route through the same SE. When SNAT is disabled, it is recommended that the session idle timeout is kept to a lower value.

    2. Enable Per-Packet Load Balancing to consider every UDP packet as a new transaction. When disabled, packets from the same client source IP and port are sent to the same server.

      Per-Packet Load Balancing: By default, NSX Advanced Load Balancer treats a stream of UDP packets from the same client IP:Port as a session, making a single load balancing decision and sending subsequent packets to the same destination server. For some application protocols, each packet must be treated as a separate session that can be uniquely load balanced to a different server. DNS is one example where enabling per-packet load balancing causes NSX Advanced Load Balancer to treat each packet as an individual session or request.

    3. Enter the Session Idle Timeout (between 2-3600 seconds). It is the amount of time a flow needs to be idle before it is deleted.

      Session Idle Timeout: Idle UDP flows terminate (time out) after a specified time period. Subsequent UDP packets could be load balanced to a new server unless a persistence profile is applied.

  6. Click Save.