Accessing the modem through the router

• This how-to describes the method for accessing the modem connected to your OpenWrt router.
• It helps to reach the administrative interface of a DSL/DOCSIS/HGU/ONT modem operating in the bridge mode.
• The prerequisite is to know the modem's IP address, port/protocol and username/password.

• Access the modem operating in the bridge mode through the router.

Assuming your modem's IP address is 192.168.100.1 and it is connected to the router's WAN interface.

1. Navigate to LuCI → Network → Interfaces.
2. Click Add new interface... and specify:
   • Name: modem
   • Protocol: Static address
   • Interface: @wan
3. Click Create interface.
4. On the General Settings tab specify:
   • IPv4 address: 192.168.100.2
   • IPv4 netmask: 255.255.255.0
5. On the Firewall Settings tab specify:
   • Create / Assign firewall-zone: wan
6. Click Save, then Save & Apply.

Make sure the modem subnet doesn't overlap with your LAN, otherwise change the LAN subnet.

1. Navigate to LuCI → Network → Interfaces.
2. Click Edit on the lan interface and change the IP address:
   • IPv4 address: 192.168.2.1
3. Click Save, then Save & Apply and then Apply unchecked.

At this point the modem should be reachable from any host in the LAN.

If you are using the BanIP package, make sure to add the IP to the allowlist. Ex. 192.168.100.0/24

Assuming your modem's IP address is 192.168.100.1 and it is connected to the router's WAN interface.

Set up a static WAN alias and assign it to the WAN zone.

# Configure network
uci -q del network.modem
uci set network.modem="interface"
uci set network.modem.proto="static"
uci set network.modem.device="@wan"
uci set network.modem.ipaddr="192.168.100.2"
uci set network.modem.netmask="255.255.255.0"
uci commit network
service network restart
 
# Configure firewall
uci del_list firewall.@zone[1].network="modem"
uci add_list firewall.@zone[1].network="modem"
uci commit firewall
service firewall restart

Make sure the modem subnet doesn't overlap with your LAN, otherwise change the LAN subnet.

# Configure network
uci set network.lan.ipaddr="192.168.2.1"
uci commit network
service network restart

If the WAN L2 device doesn't match L3 device like in case of PPPoE, change the modem interface.

# Fetch WAN L2 device
. /lib/functions/network.sh
network_flush_cache
network_find_wan NET_IF
network_get_physdev NET_L2D "${NET_IF}"
 
# Configure network
uci set network.modem.device="${NET_L2D}"
uci commit network
service network restart