DIGI One SP seems to fall asleep and needs a reboot in order to telnet to the serial device it's connected to.

Following a reboot I can telnet to port 2001 and establish a connection to the serial device. After disconnecting the telnet session and leaving it idle for about 15 minutes I cannot re-establish the connection.

I receive [TELNET] TCP error: receive failed.

I am able to connect to the DIGI One SP with a browser, log in and reboot it. Then I am able to telnet to port 2001 and establish a connection to the serial device again.

How can I prevent having to reboot each time?

Sounds like the connection is not getting closed. Try implementing a keepalive to kill stale connections:


I thought this was going to work since after implementing it I was able to connect after leaving it idle for 12 hours. But by the second day the same problem was back, I could no long establish a telnet connection to the device until I performed a reboot.

Are you able to telnet to the unit in general (i.e. not directly to the serial port)? If so, try logging in as root and issue the who command to see with, if anything, is connected to the port.

No I am not able to telnet to the unit in general when it gets in this state. I get the same result attempting to connect to port 23 or 2001. I am able to connect via http without issue. After a reboot I am able to connect to both ports.

Have you confirmed the latest firmware has been applied from the Digi web site?

Is this something that had been working for some time or is this a new deployment?

When in the bad state, if you navigate to the web interface as root, what is shown for Connections and the Device Information > Serial Ports & Diagnostics > Port 1 statistics?

This is a new device I purchased to resolve the need for remote access to some equipment. It is NOT an existing installation that started exhibiting new behavior. Yes, I updated the firmware before installing the unit.

Device Information:
Model: Digi One SP
Firmware Version: Version 82000774_W1 02/16/2016
MAC Address: 00:40:9D:97:CF:4E

CPU Utilization: 6%
Up Time: 1 days 5 hours 17 minutes 11 seconds

IP Address: xxx.xxx.xxx.xxx
Host Name:

Connections shows some connection history but no active connections. Of course the device has a public facing address so it shows many attempts to connect. Here’s a snipet:

2 None Logging In 0 Disconnect…
3 None Logging In 0 Disconnect…
4 None Logging In 0 Disconnect…
5 None Logging In 0 Disconnect…
6 None Logging In 0 Disconnect…

Looks like the device is getting bombarded with connections causing it to run out of sockets. This would explain the behavior you are seeing. I recommend implementing some security on the unit. See page 94 in the following guide:


Thanks for the information. I went ahead and restricted access to all but two of my subnets and though it does seem to block connections from logging in, it doesn’t seem to prevent socket usage from restricted addresses leaving me with the same problem unless I’m missing something.