for Linux support we need policy routing (ip rule + ip route)

[normaluser-nobody]

Unfortunately on linux IP address binding != interface binding. Linux uses the route which has the lowest metric inspite of specifying the source IP address. Therefore, we need custom ip rule and ip route configurations. I wrote a script that does this.

`#!/bin/bash

echo "=== Auto Routing Script ==="

Define interface names and their custom table IDs

declare -A interfaces=(
["wlp0s20f3"]=101
["enp0s20f0u1"]=102
["eth1"]=103
)

Check if interface exists

interface_exists() {
ip link show "$1" &>/dev/null
}

ensure_rt_tables() {
# Ensure directory exists
if [ ! -d /etc/iproute2 ]; then
echo "/etc/iproute2 missing, creating..."
sudo mkdir -p /etc/iproute2
fi

# Ensure file exists
if [ ! -f /etc/iproute2/rt_tables ]; then
    echo "/etc/iproute2/rt_tables missing, creating..."
    sudo touch /etc/iproute2/rt_tables
fi

# Add entries only if interface exists
for iface in "${!interfaces[@]}"; do
    if interface_exists "$iface"; then
        table_id=${interfaces[$iface]}
        table_name="${iface}_table"
        if ! grep -q -E "^$table_id[[:space:]]+$table_name$" /etc/iproute2/rt_tables; then
            echo "Adding entry to /etc/iproute2/rt_tables: $table_id $table_name"
            echo "$table_id $table_name" | sudo tee -a /etc/iproute2/rt_tables > /dev/null
        else
            echo "Entry $table_id $table_name already exists in /etc/iproute2/rt_tables"
        fi
    else
        echo "Skipping $iface: interface not found"
    fi
done

}

Call it for table creation and editing

ensure_rt_tables

Get IPv4 and IPv6 addresses

get_ip_addresses() {
interface=$1
ipv4=$(ip -4 addr show "$interface" | grep -oP 'inet \K[\d.]+' | head -1)
ipv6=$(ip -6 addr show "$interface" | grep -oP 'inet6 \K[0-9a-f:]+' | grep -v '^fe80' | head -1)
echo "$ipv4 $ipv6"
}

Get link-local IPv6 address (optional, for debugging)

get_link_local_ipv6() {
interface=$1
ip -6 addr show "$interface" | grep -oP 'inet6 \K[0-9a-f:]+' | grep '^fe80' | head -1
}

Get IPv4 default gateway for a specific interface

get_gateway_ipv4() {
interface=$1
ip route show default | grep "dev $interface" | awk '{print $3}' | head -1
}

Configure routing for an interface

configure_interface() {
interface=$1
table_id=$2
table_name="${interface}_table"

echo "Configuring interface: $interface (Table ID: $table_id)"

# Get IPs
read ipv4 ipv6 <<< $(get_ip_addresses "$interface")
linklocal=$(get_link_local_ipv6 "$interface")

echo "  IPv4 Address: ${ipv4:-None}"
echo "  IPv6 Address: ${ipv6:-None}"
echo "  Link-local IPv6: ${linklocal:-None}"

# Flush old routes in table
ip route flush table "$table_name" 2>/dev/null
ip -6 route flush table "$table_name" 2>/dev/null

# Remove old IPv4 rules pointing to this table
ip rule | grep "lookup $table_name" | while read -r rule; do
    prio=$(echo "$rule" | awk -F: '{print $1}')
    ip rule del priority "$prio" 2>/dev/null
done

# Remove old IPv6 rules pointing to this table
ip -6 rule | grep "lookup $table_name" | while read -r rule; do
    prio=$(echo "$rule" | awk -F: '{print $1}')
    ip -6 rule del priority "$prio" 2>/dev/null
done

# Configure IPv4
if [ -n "$ipv4" ]; then
    gateway=$(get_gateway_ipv4 "$interface")
    if [ -n "$gateway" ]; then
        ip route add "$(ip -4 route show dev "$interface" | grep -oP '\d+\.\d+\.\d+\.\d+/\d+')" dev "$interface" src "$ipv4" table "$table_name"
        ip route add default via "$gateway" dev "$interface" table "$table_name"
        ip rule add from "$ipv4" table "$table_name" priority $((20000 + table_id))
    else
        echo "  ⚠️  No IPv4 gateway found for $interface, skipping IPv4 route setup."
    fi
fi

# Configure IPv6
if [ -n "$ipv6" ]; then
    ipv6_subnet=$(ip -6 addr show dev "$interface" | grep -oP 'inet6 \K[0-9a-f:]+/[0-9]+' | head -1)
    ipv6_gw=$(ip -6 route show default dev "$interface" | awk '/default/ {print $3}' | head -1)

    if [ -n "$ipv6_gw" ]; then
        echo "  IPv6 Gateway: $ipv6_gw"

        if [[ "$ipv6_subnet" =~ / ]]; then
            ip -6 route add "$ipv6_subnet" dev "$interface" src "$ipv6" table "$table_name" 2>/dev/null
            ip -6 route add default via "$ipv6_gw" dev "$interface" table "$table_name" 2>/dev/null
            ip -6 rule add from "$ipv6" table "$table_name" priority $((30000 + table_id)) 2>/dev/null
        else
            echo "  ⚠️  Invalid IPv6 subnet format: $ipv6_subnet, skipping IPv6 route setup."
        fi
    else
        echo "  ⚠️  No IPv6 gateway found for $interface, skipping IPv6 route setup."
    fi
fi

}

Main

for interface in "${!interfaces[@]}"; do
if interface_exists "$interface"; then
configure_interface "$interface" "${interfaces[$interface]}"
else
echo "Interface $interface does not exist. Skipping."
fi
done

Show results

echo -e "\nCurrent IPv4 routing rules:"
ip rule show

echo -e "\nCurrent IPv6 routing rules:"
ip -6 rule show
`

[normaluser-nobody]

auto_network_switch.txt