Workstation using assigned ISP

Ken Graser
Ken Graser used Ask the Experts™
I'm running a Sophos XG 115 with dual ISPs (Comcast and AT&t) in balance mode.  That all works fine.  However I have one user (the Boss) who wants his workstation to always use Comcast (some of the sites he using require Comcast login).  

My question is:
Is there any way that I configure his workstation to only use the Comcast connection and not the AT&T connection?
Or is this something that has to be set up in the Sophos?

All of my workstations are using Static IPs.  

Any assistance would be appreciated.

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NoahHardware Tester and Debugger

Hi there! :)

You need to create a DNAT. You may refer to the following article for step by step instructions recommended by the official Sophos Support team.


Fractional CTO
Distinguished Expert 2018
You can create a manual route. Noah suggests one way to do this.

And, normally this is a bad idea.

Most network devices which aggregate several ISPs will load balance, also using QOS, to ensure fastest or most stable packet flow for every protocol.

If you force one/some computers to force packet flow through one ISP, all this logic is broken.

Many times this causes connections to run slow or just stop, as a forced ISP packet flow slows or stops.

Creating manual routes breaks the entire reason for running an ISP aggregator.

Tip: These devices are always smarter than human guessing, so best let your devices do their job, rather than work around them.
Ken GraserIT Manager


Thanks for the info on doing the DNAT.  I do think that would work however I need to do some testing to see what impact this would have on the load balancing etc.

You gave me some good advice and I can see where that could cause problems.  I just have to think of a good way to tell the Boss that he will have to live with it.  My network is working well and I don't want to mess it up.

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