Replacing Frontier’s Router with OpenWrt and Static IPs (A Wild Ride)

Alright, let’s talk about Frontier’s router. If you’ve ever tried to replace it with your own OpenWrt setup, you’ve probably screamed into the void like I did. Their documentation? Nonexistent. Their router? Blocking my DNS queries on UDP 53. (Yes, the router. Not Frontier. You’re welcome for that revelation.)

But hey, I survived—and now you can too! Here’s my slightly chaotic journey of getting Frontier’s static IPs working on OpenWrt.

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Step 1: Figure Out What You’re Dealing With

Frontier’s setup goes like this:

1. A WAN IP that might be dynamic or static. (Mine was static, but good luck finding out.)
2. A static IP block routed through that WAN IP. (Their router conveniently didn’t explain this either.)

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Step 2: VLANs, Bridges, and Tears

1. Go to Network > Switch in OpenWrt and create a new VLAN for your WAN interface.
2. Bridge it. Why? Because that’s what makes this magic work.

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Step 3: WAN IP Setup

Add the WAN IP and gateway under Network > Interfaces:

• WAN IP: Something like 192.0.2.10/25.
• Gateway: Probably 192.0.2.1.

Pro tip: If your ISP uses PPPoE, now’s the time to enter your credentials. (And don’t forget to breathe.)

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Step 4: Scripts Are Your Friend

Save this script as /etc/firewall.user. It does the heavy lifting with NAT and forwarding rules, dynamically handling high or low gateway setups.

#!/bin/sh
# Define the static IP block
subnet="192.0.2.0/29"
override_gateway="192.0.2.6"

start_ip=$(ipcalc $subnet | grep HostMin | awk '{print $2}')
end_ip=$(ipcalc $subnet | grep HostMax | awk '{print $2}')
gateway=$(ipcalc $subnet | grep Gateway | awk '{print $2}')

if [ -n "$override_gateway" ]; then
    gateway=$override_gateway
fi

base_subnet=$(echo $start_ip | cut -d'.' -f1-3)
start_octet=$(echo $start_ip | cut -d'.' -f4)
end_octet=$(echo $end_ip | cut -d'.' -f4)
gateway_octet=$(echo $gateway | cut -d'.' -f4)

if [ "$gateway_octet" -eq "$start_octet" ]; then
    exclude_gateway=$start_octet
elif [ "$gateway_octet" -eq "$end_octet" ]; then
    exclude_gateway=$end_octet
else
    exclude_gateway=$gateway_octet
fi

for i in $(seq $start_octet $end_octet); do
    if [ "$i" -eq "$exclude_gateway" ]; then
        continue
    fi

    ip="$base_subnet.$i"
    iptables -t nat -I PREROUTING -d $ip -j DNAT --to $ip
    iptables -t nat -I POSTROUTING -s $ip -j SNAT --to $ip
    iptables -I FORWARD -d $ip -j ACCEPT
    iptables -I FORWARD -s $ip -j ACCEPT
done

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Step 5: Enabling Proxy ARP

Here’s the cool part. You can configure Proxy ARP in OpenWrt without manually poking around /sys. Just add this to your WAN interface in /etc/config/network:

option ip4table 'main'
option proxy_arp '1'

Restart everything. Pray. (But mostly restart everything.)

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Step 6: Make Sure firewall.user Is Running

Add this to /etc/config/firewall so OpenWrt actually runs your script:

config include
option path '/etc/firewall.user'

Then:

/etc/init.d/firewall restart

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Conclusion

Congrats! You’re officially smarter than the Frontier router. If this worked for you, let me know. If it didn’t, let’s troubleshoot and cry together.