How to Implement Policy-Based Routing in Windows: Split Traffic Between LAN and 3G Interfaces

When dealing with multiple network interfaces in Windows (like corporate LAN and 3G), the system's default routing behavior often needs manual adjustment. From your route print output, I notice multiple default gateways competing, with the 3G interface currently winning due to its lower metric.

Interface 40: Vodafone Mobile Connect (3G)
Interface 11: Broadcom NetXtreme (LAN)
Multiple default routes with:
    0.0.0.0/0 via 10.183.148.5 (metric 4235)
    0.0.0.0/0 via 10.183.148.6 (metric 4235)
    0.0.0.0/0 via 10.183.148.7 (metric 4235)
    0.0.0.0/0 via on-link (10.57.175.79, metric 31)

Here's how to force corporate LAN traffic (10.183.0.0/16) through your wired interface while using 3G for everything else:

Step 1: Clean Up Existing Routes

First, remove conflicting default routes:

route delete 0.0.0.0 mask 0.0.0.0 10.183.148.5
route delete 0.0.0.0 mask 0.0.0.0 10.183.148.6
route delete 0.0.0.0 mask 0.0.0.0 10.183.148.7

Step 2: Set Up Specific Routes

Add routes for your corporate network via the LAN interface:

route -p add 10.183.0.0 mask 255.255.0.0 10.183.148.1 if 11

Step 3: Set 3G as Default Gateway

Configure the 3G interface as your default route with a lower metric:

route -p add 0.0.0.0 mask 0.0.0.0 10.57.175.79 if 40 metric 20

After implementation, verify with:

route print
ping 10.183.148.1
tracert google.com

Common issues to watch for:

Interface indexes might change after reboots
Corporate VPNs might override your routing table
3G connection drops might require route adjustments

For more robust management, create a PowerShell script:

# Get interface indexes
$3GIndex = (Get-NetAdapter -Name "Vodafone*").ifIndex
$LANIndex = (Get-NetAdapter -Name "Broadcom*").ifIndex

# Remove existing default routes
Get-NetRoute -DestinationPrefix "0.0.0.0/0" | Remove-NetRoute -Confirm:$false

# Add corporate routes
New-NetRoute -DestinationPrefix "10.183.0.0/16" -InterfaceIndex $LANIndex -NextHop "10.183.148.1"

# Set 3G as default
New-NetRoute -DestinationPrefix "0.0.0.0/0" -InterfaceIndex $3GIndex -NextHop "10.57.175.79" -RouteMetric 20

When working with multiple network interfaces in Windows (like corporate LAN + 3G/4G connections), you often need fine-grained control over which traffic goes through which interface. The default routing behavior might not always match your requirements.

From your route print output, we can observe:

IPv4 Route Table
===========================================================================
Active Routes:
    Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0     10.183.148.5   10.183.148.157   4235
          0.0.0.0          0.0.0.0     10.183.148.6   10.183.148.157   4235
          0.0.0.0          0.0.0.0     10.183.148.7   10.183.148.157   4235
          0.0.0.0          0.0.0.0         On-link      10.57.175.79     31

Here's how to configure specific routing for your case:

Step 1: Make 3G the Default Route

route delete 0.0.0.0 mask 0.0.0.0
route add 0.0.0.0 mask 0.0.0.0 10.57.175.79 if 40 metric 1

Step 2: Add Corporate LAN Routes

route add 10.183.148.0 mask 255.255.255.0 10.183.148.1 if 11 metric 1

Add the -p flag to make routes survive reboots:

route -p add 10.183.148.0 mask 255.255.255.0 10.183.148.1 if 11 metric 1

After making changes, verify with:

route print

For modern Windows versions, consider using PowerShell:

New-NetRoute -DestinationPrefix "10.183.148.0/24" -InterfaceIndex 11 -NextHop 10.183.148.1
Set-NetIPInterface -InterfaceIndex 40 -InterfaceMetric 1

If your corporate network uses multiple subnets:

route -p add 10.183.0.0 mask 255.255.0.0 10.183.148.1 if 11
route -p add 10.184.0.0 mask 255.255.0.0 10.183.148.1 if 11

Common issues and solutions:

Metric conflicts: Always check interface metrics with netsh interface ip show config
Interface indexes: Verify with get-netadapter | select ifIndex,Name
DNS considerations: Remember to configure corporate DNS servers appropriately

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