Errors 15 and 11/12: UDP ports



Errors 15, 11 and 12 are FASP errors that refer to problems with the UDP ports required for establishing a connection between an Aspera client and server. If this connection cannot be made, transfers will fail.

Usually this error is due to firewalls or other devices that may be blocking communication to and from the UDP ports.

Examples of this error

This error can manifest itself in several ways, including in the GUI application for your server, the command line if you’re transferring with ascp, and in the transfer log file.

GUI and ascp

When a client tries to make a transfer to or from a server and a connection between UDP ports cannot be established, you will see the following error message:

Client unable to connect to server (check UDP port and firewall)

On the server side, the following error message will result:

Server unable to hear from client (check UDP port and firewall)

Log file

Below is an example of these errors as they can be recorded in the logs. The aspera-scp-transfer.log file records helpful information for each attempted transfer, labelled by the date and time attempted. For a reference of the location of this log file on your system, please see this article (Where are the Client or Server logs located?).

2015-09-18 11:47:53 [1e64-00002714] ERR FASP sender had error, errcode 11 errstr [Client unable to connect to server
(check UDP port and firewall)]2015-09-18 11:47:53 [1e64-00002714] ERR Peer FASP receiver had error, errcode 12
errstr [Server unable to hear from client (check UDP port and firewall)]
2015-09-18 11:47:53 [1e64-00002614] LOG FASP Session Stop uuid=879dfcdb-015f-4945-a5b0-fdc9512a5a13 op=send
status=failed errcode=15 errstr="Timeout establishing UDP connection (check UDP port and firewall)"


Make sure the port for Aspera transfers is open and not being blocked by a firewall on both the client and server. The default UDP port is 33001.

For Windows, you can check and configure your firewall by following the instructions at the following article: Configuring Windows Firewall to enable Aspera FASP transfers.

On many Linux systems the default firewall can be configured with iptables. You will have to allow all incoming and outgoing traffic on UDP port 33001 (or whatever your Aspera UDP port is), which you can do with the following commands:

# iptables -I INPUT -p udp --dport 33001 -j ACCEPT
# iptables -I OUTPUT -p udp --dport 33001 -j ACCEPT

On Mac, if the system firewall is turned on, make sure the necessary Aspera connections are allowed. You can see and configure the allowed connections in System Preferences > Security & Privacy > Firewall. At minimum, the following should be allowed connections:

  • /Library/Aspera/bin/ascp
  • /Applications/Aspera Enterprise Server
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