Dual Ethernet port PC routing issue

Question

I have two ports on my PC. I have configured them on two different subnets. Eth#1 connects to the internet thru a Comcast router. Eth#2 is normally disabled unless I want to use my VPN router to access work resources.

When I enable Eth#2 (and don't disable Eth#1) web access slows down or becomes unpredictable. If I disable Eth#1 everything works like it should. I should mention, that both subnet masks are 255.255.255.0.

Question, what modification should I make to the pc (routing table?) to be able to keep both ports enabled without adverse effects? Diagram Below.

Answer 1

If you're running Windows, check the output of your route print command. You will see an entry for:

0.0.0.0 0.0.0.0 [Gateway IP] [Interface IP] [Metric]

It sounds like your traffic is probably going through your VPN tunnel when that is active. Since your VPN client is offloaded to an external device (VPN router), you will have no software options for split tunneling.

To solve this, insert this default route in your routing table like this:

route ADD 0.0.0.0 MASK 0.0.0.0 [Comcast Router IP] METRIC [number lower than other default route's metric]

EDIT: Just wanted to add, this will default all web traffic through your Comcast router like normal and as long as you see the entries for your work resources (1.2.3.4 255.0.0.0 ... whatever work subnets) in your route print output, then specific traffic to those will go out the interface/gateway specified there, which should be 192.168.13.1 since that's the only interface capable of learning those subnets.