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A question often posted in this forum concerns how to go about "using to routers together" or "extending wifi" using extra routers. Following is a...
A) Short Version
B) Long version
C) Backgound Information
Special and or customised firmware for routers should not be necessary.
EDIT 2014: - I've attached a "block diagram" to this post which in conceptual terms illustrates how a typical SOHO router functions. Actual implementation will of course vary, (for example, the NAT/Firewall could be argued to be part of the same "thing," the DHCP could be bound to the switch,) and some have additional features, but the basic conceptual functionality seems to hold for most SOHO routers. For routers with built in modems, the modem effectively sits between the "WAN" and "NAT" as I've drawn it. A.B.C.D and W.X.Y.Z show (respectively) where "WAN" and "LAN" IP addresses are bound logically as I've drawn it.
Short Version
1. Change the IP address of all secondary (non-ISP connected) routers so that they are unique within your LAN.
2. Disable the DHCP Server in all secondary routers.
3. Connect secondary routers to primary (ISP connected) router using their "LAN" not their "WAN/Internet" ports.
Long Version
1. Decide which is to be your "primary" (ISP connected) router. All other routers are "secondary" for the purposes of this discussion.
2. Surf to the admin screen of your primary router and make a note of it's "LAN" IP address and the range of IP addresses it's DHCP Server provides.
In SOHO kit, these will very probably be a variant of 192.168.x.y. Ensure you have a "spare" IP addresses available for each secondary router. Note that these need to be outside the range provided by the primary routers DHCP Server and not in use by anything else. See end of this post for further information on IP addressing.
3. Disconnect a "configuration computer" that you will use to set this regime up from everything and turn off it's Wi-Fi if it has it.
For each secondary router:
4. Physically disconnect it from everything then connect the configuration computer to the secondary router (LAN port) and allow the PC to acquire an IP address from the secondary router.
5. Surf to the secondary router's admin screen.
6. Set the router's LAN address to one of the "spare" addresses determined previously. Some routers may drop your connection at this point and/or require a reboot. If necessary, do so. The router may also have changed the DHCP range it serves out (leaving your configuration computer with a "wrong" IP address,) so a reboot of the confguration computer to cause it to acquire a new IP address might be necessary. Thence surf back to the router's admin screen using the new IP address you just gave it.
7. Find the secondary router's DHCP Server settings (note "Server" not "Client") and turn the DHCP Server off. The only functioning DHCP Server in your network should be the one in your ISP connected "primary" router.
8. Repeat from step "4" for any additional secondary routers.
9. Connect your secondary routers to you primary router (or each other or anything else) using their "LAN" and not their "WAN" AKA "Internet" ports. The WAN/Internet ports on your secondary routers shall forever have nothing connected to them.
10. Reconnect the configuration computer as you would in normal use and enable it's Wi-Fi if you turned it off earlier. Again a reboot of the PC may be necessary to pick up an IP address issued by your primary router.
11. Set up Wi-fi on each router as desired.
12. You might also care label each router with it's IP address. It's surprising how quickly one forgets.
Backgound Information
The things that we all know as "routers" are rather badly named. They are multi-function devices containing (for example) a modem, ethernet switch, router, firewall, NAT translator, DHCP Server and Wi-Fi Access Point amongst others. Note that last item - Wi-Fi is availed by Access Points. An Access Point is built-in to that thing we have at home we call a "router." It is possible to build a perfectly good multi-cell Wi-Fi network using Access Points. "Routers" are not necessary to "do Wi-Fi."
It is not uncommon for people to believe that Wi-Fi is availed by "routers" but we now know this is not the case. When SOHO routers first entered the market place, they didn't contain Wi-Fi Access Points, but were otherwise identical to the "Wi-Fi Router" that we know today.
So why do people use routers as Wi-Fi Access Points? Sometimes it's because they have an old one lying around, or can buy them cheaper than a stand alone Access Point, most notably on the online auction sites. Sometimes it's because they also want a few extra ethernet ports as well as Wi-Fi and using a router is a convenient way to avail a little AP/switch combo box at low cost.
To use routers as an AP or AP/switch combo, we need to (ironically) not use it's routing, NAT, firewall and a few other functions. No problem so far, if we simply leave the WAN/Internet port disconnected and cable routers together using their LAN ports, we achieve this.
However, a further problem occurs with DHCP. Most SOHO routers have a DHCP Server built in to automatically provide IP addresses to any client devices connected to them. A router's DHCP Server is often pre-configured to distribute IP addressing information that designates itself as being the point of contact for the rest of the world. Essentially the IP addressing information they provide says "if you want to connect to something outside your local network (LAN,) talk to me and I'll forward the request on for you."
That's fine in a little SOHO LAN with only one router, but becomes problematic when we have multiple routers (with the secondaries having nothing connected to their WAN/Internet ports) as the secondary routers cannot handle the requests to connect to the outside world.
The easiest way to deal with this, is to ensure that all the IP addressing is handled by your primary, ISP connected router that does know how to talk to the world. The easiest way to achieve this, is to disable the DHCP Server on all the secondary routers so that only the primary router gives out IP addresses.
On an IP LAN, every device must have a unique IP address. Each router is one such device. Often they ship pre-configured to some common default IP address. 192.168.0.1 and 192.168.1.1 for example. If you connected two routers from the same manufacturer or of the same model together it's very like they will have the same IP address - the manufacturers generally don't randomise them - and duplicate IP addresses are a no-no.
Hence, we need to ensure that all our routers have a unique IP address. And if we ever want to access them in future, say to adjust their setting or update the firmware, that will be much easier to do if they are all in the same "subnet" range as it's known. Without getting terribly boring about how IP addressing works, if you use subnet mask 255.255.255.0 on your LAN, (most SOHO kit seems to by default,) and IP addresses of the format 192.168.X.Y; keep "192.168.X" the same on everything and make sure "Y" is unique, outside your primary routers DHCP range, not "0" or "255" and between 1 & 254.
EDIT 2017: Don't worry if secondary routers "complain" that the "Internet isn't there." E.G. Some BT HomeHubs flash their blue "broadband" lights constantly, other routers show error messages in the admin screens. This is expected.
Most SOHO routers "expect" to find the Internet through their WAN/Internet ports and aren't designed to "look" for it anywhere else. Using the regime described in this FAQ, by definition, all "secondary" routers have no connection to their WAN/Internet ports and thus cannot find the Internet through them and are not designed to seek the Internet anywhere else. So they may generate error states.
But that's OK, if you've configured things as described in this FAQ, the client devices will be finding their way the the Internet through your ISP connected "primary" router and we can ignore any error messages on the secondary routers about Internet not being available. Indeed, if the "light" gets irritating, some routers may let you "disable" the Internet in their UI (though many don't.)
I think that's everything. If anyone one finds any errata, or one of my frequent spolling or granma erros, PM me. |
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2-12-2019 04:24:16
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