UDP Port Reuse

When an ascp server is running on Windows, concurrent transfers cannot bind to the same UDP port. Each concurrent transfer will bind to the next open port starting from the default port of 33001.

When the nodes behind the reverse proxy server are Windows hosts, the iptables rules that are created must account for this and create a rule that routes traffic from a UDP port on the proxy server to a UDP port on the destination host. To enable this feature set the <udp_port_reuse> option to false. When set to false, reverse proxy creates rules where each concurrent transfer through the proxy server gets an incremented UDP port number for the clients to send to. Then the iptables rule routes the traffic from that port to the ascp server's port. In this scenario, the UDP ports are incremented by 1 with each concurrent connection. The following diagram shows how the UDP ports on the proxy server and the Windows target are updated with each concurrent transfer.

In prior versions of IBM Aspera Proxy, this configuration could be achieved by setting <proxy_port> to 0. However, setting it to zero is no longer supported and now results in an error.

For information about how to set up load balancing when <udp_port_reuse> = false, see Load Balancing.

Note: When setting <udp_port_reuse> to false, and thereby enabling the use of incremented UDP port numbers, make sure the UDP ports specified by <proxy_port> are open on the external firewall.