PfSense, VLAN’s, and SSH Disconnects (and how to fix it)

For the past month or so my storage box has been driving me insane. Whenever I SSH into the box, after about 30 seconds it would always disconnect me. I checked everything from routes, to firewall rules, and nothing was amiss. I spent weeks looking for the cause of these SSH Disconnects, but to no avail. That is, until recently. After some extreme googling, I was able to figure out the cause and I had to share it.

On the server in question, I have it hooked up to two networks. One vi cable, and another using a VLAN tag on the same port. If I were to take down the VLAN interface, or the direct cable interface, then SSH would not have any disconnect issues. This lead me to believe it was a routing issue, or a network configuration problem. Well in the end, I found the cause to be none other then my firewall, PfSense!

After finding a thread on their forum with someone who shared my troubles, I was able to find a solution and I felt it should be shared. (That said thread is linked at the bottom of this post).

So, lets get started!

  1. Login to your PfSense firewall
  2. Go to System > Advanced > Firewall / NAT
  3. Set Firewall Optimization Options to Conservative
  4. Enable Clear invalid DF bits instead of dropping the packets

In the end, it should look like this:

PfSense Firewall Settings to fix SSH Disconnects

 

 

 

 

 

After this, my SSH disconnects completely disappeared! I hope you find this as useful as I did.

Citation:

http://forum.pfsense.org/index.php?topic=35203.0

9 thoughts on “PfSense, VLAN’s, and SSH Disconnects (and how to fix it)

  1. Pingback: SSH connection through UTM 9 VM dropping after 1 min - Sophos User Bulletin Board

  2. Tilghman Lesher

    Excellent! That worked for us, as well, although our symptoms were slightly different. During backup times, when the network was being stressed, this would occur to long-running persistent SSH connections. This change has allowed those sessions to remain connected.

    Reply
  3. Oliver

    I tried that solution, and at the first look it worked
    But the problem must be elsewhere. If you take a look at the help page of pfSense it shows that in the “normal” Firewall mode “tcp.opening No response yet” get terminated after 30secs which is the time ssh takes to disconnect.
    https://doc.pfsense.org/index.php/Advanced_Setup#Firewall.2FNAT

    In “conservative” mode this time is just increased to 15min!
    So i waited for 15min instead of 30sec -> and the same problem occured.

    Do you have any idea what else it could be?

    Reply
  4. Dave W

    Thank you!!!! That has been driving me crazy for the last few days. I’ve been configuring a pfSense for our new external connection and switched to using it as my gateway to test.
    As soon as I did that, and configured the VLANs on pfSense, the SSH to the switched kept bombing out after a couple of minutes.
    I thought I had configured the VLANs wrong or that the box we are using wasn’t up to the task… Then I stumbled on your post.

    Reply

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