Seperate Lan and WLan

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While Linksys never intended their WRT54G/GS router to allow multiple local networks, it is possible to seperate the WLan network from the Lan network and allow both to independently access the internet. Since this was not supported by the original Linksys firmware, and all custom firmwares are a derivation of this, performing this setup will yield some somewhat unexpected results when configuring certain options from the Web Interface. (For example, advanced Routing from the Web Interface, when directing to the WLan & Lan port, it will actually only go to the Lan port, etc). Users wishing to perform this setup should be very familiar with the command line interface, as those Web Interface configurations broken by this setup can still be set from the command line interface.

Users wishing to configure their routers this way might choose to install the OpenWRT firmware instead as it does not offer a web interface that can get screwed up.

Keep in mind that Brainslayer is currently in the processes of merging DD-WRT with OpenWRT. While it was already true that things said for OpenWRT were likely the same or similar for DD-WRT since they both share the same Linksys firmware roots, this statement is even more true now and will eventually read: Things said for OpenWRT can be said for DD-WRT. We are not there yet.


Physically the WRT54G is a 2 port router and a 6 port switch. 1 Port of the switch is connected to the router. 1 Port of the Switch is the WAN port. The other 4 ports of the switch are the 4 LAN ports seen on the back of the router. The remaining port on the router is connected to the WLAN adapter.

By default, inside the switch exist 2 Virtual LANs (VLans), vlan0 and vlan1. vlan0 contains ports 1-4 (Lan ports) and port 6 (router). vlan1 contains port 0 (WAN) and port 6 (router). IPTables are then implemented on the router such that NAT'd routing is possible between the VLans.

By default, inside the router there is a bridge (br0) bridging eth1 (WLAN) and eth0 (switch port 0). This is what allows the WLAN and LAN to share the same IP address. When the router needs to send information to client machines, it is broadcast out br0 (sending it to eth1 and vlan0). When the router needs to send information to the WAN port, it is sent directly to vlan1.

Please read OpenWRT: OpenWRT DOCS/Configuration as it is short and quite in depth.

Configuration Overview

There are two methods for running seperate IP ranges on each of the interfaces which yeild two rather dissimilar results.

iptables method

Rather than splitting up br0, some may find it addequate to use the Iptables command to allow routing between two subnets on the LAN/WLAN side. Since br0 is not being split up, there are no/fewer problems caused in the web interface. The major draw back to this is that if wireless users statically assign an IP on the LAN ip address range, the bridge will allow them access. A trick might be to set the WLAN ip range to the default (192.168.1.x) and the LAN ip range to something odd (10.15.25.x, or 192.168.152.x or something) to prevent WLAN users from guessing the ip range.

You can use any private ip ranges you would like, but for this example I will use 192.168.1.x for the LAN ports and 192.168.2.x for the WLAN port.

Basic Steps:

Enable a static route for 192.168.1.x to vlan0
Enable a static route for 192.168.2.x to eth1
Enable DHCP for 192.168.1.x for vlan0
Enable DHCP for 192.168.2.x for eth1

Bypass the bridge method

In this method we will bypass the br0, disconnecting the Lan and the WLan ports ensuring that everything is processed inside the router. The down side with this is that Web Interface options that previously affected both the Wifi and Lan will now only affect the Lan.

Basic Steps:
After this stage, br0 is not created using the contents of lan_ifnames as would normally be the case. Services that would normally use the bridge, will now use vlan0 (since they'll query the lan_ifname variable). wifi_* variables have now been created for use with ifup. These steps need only be done once.

Set the lan_ifname nvram variable to vlan0
Set wifi_ifnam to eth1
Set wifi_proto to dhcp or static (run dhcp for wifi hosts?)
Set wifi_ipaddr to the IP you want your wifi adapter on
Set wifi_netmask to the your wifi netmask (probably
commit to nvram 

The following commands will need to be done every boot (rc_firewall perhaps?)

Enable a static route for <wireless_network> to/from eth1 and wan
Enable DHCP for <wireless_network> for eth1
Enable DNS for <wireless_network>
If you want to prevent wifi and lan from accessing each other, be sure to
 Deny traffic to <lan_adapter_network> from <wireless_network>
 Deny traffic to <wireless_network> from <lan_adapter_netowrk>

To match the above example, replace <lan_adapter_network> with 192.168.1.x and <wireless_network> with 192.168.2.x

Vlan Web Interface method

Someone experimenting in the forums discovered that by not assigning the WLAN interface to any vlan he could seperate the wireless and lan to seperate networks. He was unable to configure WEP/WDS on the wireless link, however. I don't intend to explore this option further in the wiki, as I can find no other documentation describing this type of method for other firmwares. If you don't care about WEP/WDS, this might be easier than the bypass method described above.

Basic Steps (as I understand them)

Change "Wireless to None" under VLAN in the [Web Interface]
ADD "wlconf eth1 up" to rc_startup or Wlan back up.
Enable a static route for <lan_adapter_network> to/from vlan0 and wan
Enable a static route for <wireless_network> to/from eth1 and wan
Enable DHCP for <lan_adapter_network> for vlan0
Enable DHCP for <wireless_network> for eth1

To match the above example, replace <lan_adapter_network> with 192.168.1.x and <wireless_network> with 192.168.2.x

Config Implementation

Here we will describe the actual commands needed to accompolish the basic steps overviewed above.

Using iptables

needs to be written

Bypassing the Bridge

Not yet fully tested. Do not know if wep/wds work from web config of if wl command will be needed.

Since the file /etc/network/interfaces file doesn't exist on DD-WRT as it does on OpenWRT, we have to use the ifconfig command to configure the interfaces and those wifi_* variables from before don't have a script to read them, so they're useless right now. But we can still do it manually.

For this example I'm placing the wifi on 192.168.2.x and is the LAN ip.

  If not, set to AP mode and then reboot the router.

Seperate the Bridge

nvram set lan_ifname=vlan0
nvram commit

Setup the eth1 interface

ifconfig eth1 down
ifconfig eth1 netmask
ifconfig eth1 up

Setup Routes

iptables -I FORWARD -i eth1 -p tcp -j ACCEPT
iptables -I FORWARD -i vlan1 -p -j ACCEPT  ?? required??
The above rule did say vlan0, should it be vlan1?
vlan1 is wan port... I don't think you'd want to accept everything that
comes in on the wan port, but maybe that's just me...

Setup DHCP & DNS on Wifi interface

iptables -I INPUT -i eth1 -p udp --dport 67:68 --sport 67:68 -j ACCEPT
iptables -I INPUT -i eth1 -p udp --dport 53 -j ACCEPT
killall -q -9 dnsmasq
sed /^interface.*/d /tmp/dnsmasq.conf > /tmp/
echo -n "
pidfile /var/run/
max_leases 50
interface eth1
remaining yes
auto_time 30
lease_file /tmp/udhcpd.leases
statics_file /tmp/udhcpd.statics
option subnet
option router
option lease 86640
option dns $(nvram get wan_dns)
" > /tmp/udhcpdeth1.conf
udhcpd /tmp/udhcpdeth1.conf


If you want to put your router back with the wifi and wlan bridged give the commands

nvram unset rc_firewall
nvram lan_ifname="br0"
nvram commit

Using a script to parse wifi_* Variables

This stage has not been completed. This note will be removed after it has been fully tested To make configuration easier, I've written a script that accepts wifi_* nvram variables. This is essentially how the OpenWRT firmware does this, as I understand it. After it's setup, you can change your wifi settings by simply updating the nvram variables and rebooting!

nvram set lan_ifname=vlan0
nvram set wifi_ifname=eth1
nvram set wifi_proto=dhcp
nvram set wifi_ipaddr=
nvram set wifi_netmask=
nvram commit

If you don't want your wifi to use the same dhcp settings as your lan side (same number of leases, same lease time, etc) issue these commands.
(Example will setup dhcp from with 120 minute leases)

nvram set wifi_dhcp_start=100
nvram set wifi_dhcp_num=15
nvram set wifi_dhcp_lease=120
nvram commit

Now copy this script to /jffs/etc/
Remember, only edit scripts using *nix friendly text editors (such as TextPad or win32pad).

# !/bin/sh
##### ####
# Wifi configuration script by Bob/Paul.
# Special thanks to loco on the forums for the iptables, dhcp, and dnsmasq code!!

####initialize the variables####
WIFI_INTERFACE=$(nvram get wifi_ifname)
WIFI_IPADDRESS=$(nvram get wifi_ipaddr)
WIFI_NETMASK=$(nvram get wifi_netmask)

####Basic Check for Prerequisites, toggle error####
if [ "$WIFI_INTERFACE" = "" ]; then
  ERROR="FATAL ERROR: NVRAM wifi_ifname has not been configured!"
if [ "$WIFI_IPADDRESS" = "" ]; then
  ERROR="FATAL ERROR: NVRAM variable wifi_ifname has not been configured!"
if [ "$WIFI_NETMASK" = "" ]; then
  ERROR="FATAL ERROR: NVRAM variable wifi_ifname has not been configured!"
if [ "$(nvram get lan_ifname)" = "br0" ]; then
  ERROR="FATAL ERROR: LAN and WIFI are bridged. Set NVRAM variable lan_ifname=vlan0 to unbridge"
if [ "$(nvram get lan_ifname)" = "vlan1" ]; then
  echo "ERROR: lan_ifname = vlan1"
  echo ERROR: lan_ifname = vlan1 > /tmp/wifi_config_script.error

  if [ "$(nvram get wan_ifname)" = "vlan1" ]; then
    ERROR="FATAL ERROR: LAN and WAN are BOTH vlan1!! There is no link to vlan0!!!"

#####Check for error, echo error, break####
if [ "$ERROR" != "" ]; then
  echo Error seperating wifi from lan!!
  echo Error #$RET_VAL
  echo $ERROR
  echo Script terminating

  echo -n "
  Error seperating wifi from lan!!
  Script terminating
  " >> /tmp/wifi_config_script.error

  return $RET_VAL

#####Test for extended wifi variables (wifi_dhcp_start, wifi_dhcp_num, & wifi dhcp_lease (in minutes))####

#Test for wifi_dhcp_lease
if [ "$(nvram get wifi_dhcp_lease)" = "" ]; then   #default values
 WIFI_DHCP_LEASE=$(nvram get dhcp_lease)
else                                             #else configured...
 WIFI_DHCP_LEASE=$(nvram get wifi_dhcp_lease)

#Test for wifi_dhcp_num
if [ "$(nvram get wifi_dhcp_num)" = "" ]; then
 WIFI_DHCP_NUM=$(nvram get dhcp_num)
 WIFI_DHCP_NUM=$(nvram get wifi_dhcp_num)

#Test for wifi_dhcp_start .. setup initially
if [ "$(nvram get wifi_dhcp_start)" = "" ]; then
 WIFI_DHCP_START=$(nvram get dhcp_start)
 WIFI_DHCP_START=$(nvram get wifi_dhcp_start)

#WIFI_DHCP_END can be configured from what we already know
WIFI_DHCP_END=$(echo $WIFI_IPADDRESS | cut -f1-3 -d .).$(expr $WIFI_DHCP_START + $WIFI_DHCP_NUM - 1)

#append ip address to WIFI_DHCP_START

#bring up the wifi interface with the ip and netmask
echo restarting the wifi interface
ifconfig $WIFI_INTERFACE down
ifconfig $WIFI_INTERFACE up

#setup static routes for the wifi interface
echo Writing the routing tables for forwards
iptables -I INPUT -i $WIFI_INTERFACE -p tcp -j ACCEPT
iptables -I FORWARD -i $WIFI_INTERFACE -p tcp -j ACCEPT

#allow dhcp and dns mask on the wifi interface
echo Writing the routing tables for DNS \& DHCP
iptables -I INPUT -i $WIFI_INTERFACE -p udp --dport 67:68 --sport 67:68 -j ACCEPT
iptables -I INPUT -i $WIFI_INTERFACE -p udp --dport 53 -j ACCEPT

#kill dns masq and bring it back up on the wifi and lan interfaces
echo Killing and restarting DNSMASQ
killall -q -9 dnsmasq
sed /^interface*/d /tmp/dnsmasq.conf > /tmp/
dnsmasq --conf-file /tmp/

#write a new udhcpd script for the wifi interface to /tmp/udhcpd_wifi.conf
echo Writing the udhcpd script for WIFI
echo -n "
max_leases WIFI_DHCP_NUM
remaining yes
auto_time 30
lease_file /tmp/udhcpd_wifi.leases
statics_file /tmp/udhcpd.statics
option subnet $WIFI_NETMASK
option router $WIFI_IPADDRESS
option lease $WIFI_DHCP_LEASE
option dns $(nvram get wan_dns)
" > /tmp/udhcpd_wifi.conf

#bring up udhcpd on the wifi interface
echo Running second dhcp server
udhcpd /tmp/udhcpd_wifi.conf

Now that you've save the script as a to /jffs/etc, make it executable and tell it to load on startup. Since this is basically a firewall setting, we'll add it to the rc_firewall variable. You could also use any of the methods in Startup Scripts

chmod 700 /jffs/etc/
nvram set rc_firewall="$(nvram get rc_firewall)
/jffs/etc/ $
nvram commit

Reboot and enjoy!

External Resources

A DD-WRT Forum Thread on the topic
OpenWRT FAQ: 13. Using OpenWRT as a router, instead of a bridge?
OpenWRT FAQ: what is BR0
OpenWRT Mini howto: 3.1. Individual control of all network devices
OpenWRT: How to VLans
OpenWRT: The Ethernet Switch
WLUG-Wiki - ifup(8)

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