Separate LAN and WLAN (outdated)
From DD-WRT Wiki
This guide is outdated, please see Separate LAN and WLAN instead.
While Linksys never intended their WRT54G/GS router to allow multiple local networks, it is possible to separate 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.
There are two methods for running separate IP ranges on each of the interfaces which yield two rather dissimilar results.
 iptables Method
Rather than splitting up br0, some may find it adequate 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.
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 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.
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 255.255.255.0) commit to nvram reboot
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 separate the wireless and lan to separate 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
I've been able to segregate the eth1 (WLAN) interface using the Setup > Networking tab. I just set the eth1 interface to 'unbridged'. If you want to (you probably do), you'll probably also need to add a "Multiple DHCP server", below, on the eth1 interface. I have yet to test that this actually works properly, but preliminary tests show that it does. --TheAnarcat 04:28, 12 May 2009 (CEST)
 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.
DO NOT KNOW IF MY IPTABLES COMMANDS ARE CORRECT FOR THIS OR THE SCRIPT
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 192.168.1.1 is the LAN ip.
MAKE SURE THE ROUTER IS IN AP MODE
If not, set to AP mode and then reboot the router.
 Separate the Bridge
nvram set lan_ifname=vlan0 nvram commit reboot
 Setup the eth1 interface
ifconfig eth1 down ifconfig eth1 192.168.2.1 netmask 255.255.255.0 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...
You have to set the protocol to all to be able to surf on the net correctly if you have a router behind the Wrt iptables -I FORWARD -i eth1 -p all -j ACCEPT
 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/dnsmasq.conf.new echo -n " pidfile /var/run/udhcpd.pid start 192.168.2.100 end 192.168.2.149 max_leases 50 interface eth1 remaining yes auto_time 30 lease_file /tmp/udhcpd.leases statics_file /tmp/udhcpd.statics option subnet 255.255.255.0 option router 192.168.2.1 option lease 86640 option dns $(nvram get wan_dns) " > /tmp/udhcpdeth1.conf udhcpd /tmp/udhcpdeth1.conf
If you want to put your router back with the wifi and wlan bridged give the commands
nvram unset rc_firewall nvram lan_ifname="br0" nvram commit reboot
 Using a script to parse wifi_* Variables
This stage has not been completed. This note will be removed after it has been fully tested To make configuration easier, I've written a script that accepts wifi_* nvram variables. This is essentially how the OpenWRT firmware does this, as I understand it. After it's setup, you can change your wifi settings by simply updating the nvram variables and rebooting!
nvram set lan_ifname=vlan0 nvram set wifi_ifname=eth1 nvram set wifi_proto=dhcp nvram set wifi_ipaddr=192.168.2.1 nvram set wifi_netmask=255.255.255.0 nvram commit
If you don't want your wifi to use the same dhcp settings as your lan side (same number of leases, same lease time, etc) issue these commands.
(Example will setup dhcp from 192.168.2.100-192.168.2.14 with 120 minute leases)
nvram set wifi_dhcp_start=100 nvram set wifi_dhcp_num=15 nvram set wifi_dhcp_lease=120 nvram commit
Now copy this script to /jffs/etc/wifi_config.sh
Remember, only edit scripts using *nix friendly text editors (such as TextPad or win32pad).
# !/bin/sh # ##### wifi_config.sh #### # # Wifi configuration script by Bob/Paul. # Special thanks to loco on the forums for the iptables, dhcp, and dnsmasq code!! ##Don't see the Wifi Net if not setted ;) wlconf eth1 up ####initialize the variables#### WIFI_INTERFACE=$(nvram get wifi_ifname) WIFI_IPADDRESS=$(nvram get wifi_ipaddr) WIFI_NETMASK=$(nvram get wifi_netmask) ####Basic Check for Prerequisites, toggle error#### if [ "$WIFI_INTERFACE" = "" ]; then ERROR="FATAL ERROR: NVRAM wifi_ifname has not been configured!" RET_VAL=1 fi if [ "$WIFI_IPADDRESS" = "" ]; then ERROR="FATAL ERROR: NVRAM variable wifi_ifname has not been configured!" RET_VAL=2 fi if [ "$WIFI_NETMASK" = "" ]; then ERROR="FATAL ERROR: NVRAM variable wifi_ifname has not been configured!" RET_VAL=3 fi if [ "$(nvram get lan_ifname)" = "br0" ]; then ERROR="FATAL ERROR: LAN and WIFI are bridged. Set NVRAM variable lan_ifname=vlan0 to unbridge" RET_VAL=4 fi 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!!!" RET_VAL=5 fi fi #####Check for error, echo error, break#### if [ "$ERROR" != "" ]; then echo Error separating wifi from lan!! echo Error #$RET_VAL echo $ERROR echo Script terminating echo -n " Error separating wifi from lan!! $ERROR Script terminating " >> /tmp/wifi_config_script.error return $RET_VAL fi #####Test for extended wifi variables (wifi_dhcp_start, wifi_dhcp_num, & wifi dhcp_lease (in minutes))#### #Test for wifi_dhcp_lease if [ "$(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) fi #Test for wifi_dhcp_num if [ "$(nvram get wifi_dhcp_num)" = "" ]; then WIFI_DHCP_NUM=$(nvram get dhcp_num) else WIFI_DHCP_NUM=$(nvram get wifi_dhcp_num) fi #Test for wifi_dhcp_start .. setup initially if [ "$(nvram get wifi_dhcp_start)" = "" ]; then WIFI_DHCP_START=$(nvram get dhcp_start) else WIFI_DHCP_START=$(nvram get wifi_dhcp_start) fi #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 + $WIFI_DHCP_NUM - 1) #append ip address to WIFI_DHCP_START WIFI_DHCP_START=$(echo $WIFI_IPADDRESS | cut -f1-3 -d .).$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 $WIFI_IPADDRESS netmask $WIFI_NETMASK 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.new dnsmasq --conf-file /tmp/dnsmasq.conf.new #write a new udhcpd script for the wifi interface to /tmp/udhcpd_wifi.conf echo Writing the udhcpd script for WIFI echo -n " start $WIFI_DHCP_START end $WIFI_DHCP_END max_leases $WIFI_DHCP_NUM interface $WIFI_INTERFACE 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 $(nvram get wan_dns) " > /tmp/udhcpd_wifi.conf #bring up udhcpd on the wifi interface echo Running second dhcp server udhcpd /tmp/udhcpd_wifi.conf
Now that you've save the script as a to /jffs/etc, make it executable and tell it to load on startup. Since this is basically a firewall setting, we'll add it to the rc_firewall variable. You could also use any of the methods in Startup Scripts
chmod 700 /jffs/etc/wifi_config.sh nvram set rc_firewall="$(nvram get rc_firewall) /jffs/etc/wifi_config.sh $ " nvram commit
Reboot and enjoy!
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)