Port Forwarding Troubleshooting for Digi TransPort

This document describes how to troubleshoot IP Port Forwarding (AKA Port Redirection) set up on a Digi TransPort® (SarOS) device which forward specific incoming ports from the cellular interface onto devices found on the Ethernet side of a Digi TransPort.
This article includes the WR11, WR11XT, WR21, WR31, WR44, WR44R, and WR44RR.
An article which should be referenced is the following which describes how to configure IP Port Forwarding:  Quick Note 004 – TCP/UDP port re-direction through NAT using “Static NAT Mappings” or a firewall script. (Port Redirection)
The following are some Troubleshooting Tips in case you are having issues with IP Port Forwarding:
  • The Digi TransPort must have a Mobile Terminated account.  Mobile Terminated means that the traffic originates from an application and terminates at the mobile device, in this case the Digi TransPort.  If the account is Mobile Originated, meaning the traffic originates with the mobile device and terminates at the application, then it will not work.  A question to yourself to determine the type of service your device has is:  Can you get into the WebUI of the TransPort remotely (via the cellular IP address), assuming the firewall is not blocking the traffic to the WebUI?
  • Are there typos in the IP Port Forwarding table?
  • Has the NAT setting for the cellular interface (default is PPP 1) been set to IP Address and Port?
    • In the WebUI of your TransPort, go to Configuration – Network > Interfaces > Advanced > PPP 0 - 9 > PPP1, ensure that Enable NAT on this interface is checked and then enable IP address and Port.
  • Has the PPP 1 link been dropped (you have to reboot the Digi TransPort to accomplish this – you can’t simply drop the PPP 1 link)?
  • Can you PING the Ethernet connected device from your Digi TransPort? 
    • In the WebUI, navigate to Administration - Execute a Command and then ping the end device IP address.
  • Is this device’s Default Gateway set to the Ethernet IP address of the Digi TransPort ( by default)?
  • After setting up IP Port Forwarding, does the device need to be rebooted before the change takes effect?
  • If the device(s) are connected to a switch, try either power cycling the switch or connect the Digi TransPort and the device directly to each other’s Ethernet ports. Possibly disconnecting the Ethernet cables and reconnecting them would resolve this as well.
  • Here are a couple of commands that might assist in troubleshooting.  Please go to Administration - Execute a Command and then try the following commands:
    • nat 0 ? – This will show the present Network Address Translation settings.
    • arp -a – This displays the current ARP settings.  NOTE: The MAC address should match the IP address you are trying to forward to.
If, after going through each of the bullets above you are still having issues with IP Port Forwarding, please gather the debug.txt file.  This can be accomplished either via FTP or the WebUI by going to Administration - File Management > FLASH Directory, right-click on debug.txt and select Save Target As (or whatever term your browser uses). For more details see QN24.
If this is a new case, please email us at tech.support@digi.com with the debug.txt file.  Please be sure to let us know that you have attempted each item from this Knowledge Base article.  
If this is an existing case, please reply to the previous email with the debug.txt file.  Please be sure to let us know that you have attempted each item from this Knowledge Base article.  
Last updated: Aug 18, 2022

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