[Tfug] Adventures in Wifi range extending

[John Gruenenfelder]

Greetings again TFUG,

I'm writing again to share the rsults of my recent experiment with setting up
a wifi range extender.


The situation, briefly:
Due to household layout and where the cable modem and primary wifi AP are
located, signal strength in the den, where the entertainment cernter is
located, is quite lousy.  My goal was to create a wireless link from the
primray AP to a secondary AP and have the TV and set-top boxes connect to
that, preferably via a wired connection.


The questions:
I've never attempted anything like this so I was unsure how to proceed.  Now,
all of the wifi hardware manufacturers make range extender devices, along with
many other specialized bits of hardware, but that means little in the grand
scheme.

Specifically, I had seen numerous hints online that one could turn a surplus
AP into a repeater if using the correct firmware.  I still wasn't sure if a
fairly plain AP would work or if I needed one bristling with antennae


My solution:
I purchased a second dual-band wifi AP, this time one with external antennas
just to be safe.  This new router, a TP-Link Archer C7 became the new primary
router and the previous router, an Asus RT-AC56U, became the secondary.

Having performed the process numerous times, it did not take long to install
dd-wrt onto the TP-Link and configure it to perform its basic tasks, but I did
run into a few roadblocks.  First, dd-wrt.com asks you, frequently, to always
start with the router DB and use the info it provides.  The problem is that
the DB is *way* out of date and didn't even make mention of my new router.
Google solved that with this page:
  https://www.dd-wrt.com/wiki/index.php/TP_Link_Archer_C7

The other problem with configuring dd-wrt is which of the *many* available
builds to use, especially when the DB can provide no useful information.  In
the end, I wound up using r26446 for the new TP-Link router and keeping r23940
which was already installed on the Asus router.


Repeater Bridge:
Now that I had to functional routers, it was time to link them together.
After some Googling I found a very useful howto document:
  https://www.dd-wrt.com/wiki/index.php/Repeater_Bridge

The most important thing I learned right away was that a standard repeater
configuration (assuming a single-band radio) allows only wired connections to
the secondary router as the radio is being used to connect to the primary AP.
However, you can choose to configure the secondary router as a "Repeater
Bridge" which gives you the benefit of the router->router wireless connection,
but still allows clients to connect to the secondary router as wireless
clients.

There are two (fairly minor) downsides to this configuration:
1) The instructions say that using the same SSIDs for the the networks
provided by each router is a *bad* idea and will lead to problems.  In my
neighborhood the houses are a good distance appart so this isn't really an
issue; it just means I have four wifi networks instead of two.

2) Serving wireless clients takes away time that the router could be using for
transferring data between the two routers.  In practice, though, this really
isn't a big deal.  It hadn't crossed my mind before, but once I thought about
it logically, of course it makes sense.  A radio can only ever talk to ONE
client at a time because they're all sharing the same frequency.  So, unless
you've got a client that is hogging all the bandwidth then there should always
be plenty for the router backhaul.


The result:
Since both routers are dual-band, I decided to make the router->router
connection use the 5 GHz band.  It has higher data throughput, few clients are
likely to connect in the near future, and the connection won't die everytime
somebody turns on the stupid microwave.

Most surprising was the ease with which I was able to get this to work.  I
followed the directions in the howto, making small changes where necessary,
and on my first full-fledged test... it worked!  I was surprised and
ecstatic.  I really had been planning on spending a non-trivial amount of time
tweaking the things to get them to behave.


The Aftermath:
Don't get me wrong... this setup is *very* fragile.  While, through some small
miracle, I was able to get channel bonding wokring, it's touchy.  This is
where the radio binds multiple adjacent frequency bands to increase
throughput.  I found that seemingly minor or benign changes to the channel or
bonding settings on the TP-Link would inst-kill the 5 GHz link.

Getting the channel bonding to work was important because this is prtty much
the only way to come even close to the speeds advertised on the router boxes.

Another issue is that the help provided in the dd-wrt GUI is woefully
outdated, missing items, or sometimes even wrong.  Fortunately, Google found
me the following:
  https://www.dd-wrt.com/wiki/index.php/Atheros/ath_wireless_settings
and
  https://www.dd-wrt.com/wiki/index.php/Advanced_wireless_settings

These two pages provided *much* more detail on most of the available
settings.  So, now I have a much better understanding on what many of these
options are, though the question of "why" I might want to use some of them
remains a mystery.


Remaining questions and issues:
As mentioned above, the firmware on the Asus router is a fair bit older than
the TP-Link's firmware.  I'm not sure if I should leave well enough alone, or
upgrade the Asus to make the configuration GUIs the same and to get all the
latest security updates.

If a radio can only ever talk to a single client at a time, what's the deal
with the multiple antennas?  The TP-Link has three internal 2.4 GHz and three
external 5 GHz antennas while the Asus has all internal antennas, three for
each band, I think.  Googling introduced me to MIMO (Multiple In Multiple Out)
and beamforming (implicit and explicit).  Both technologies are supposed to
increase throughput and signal strength and are usually only found on the
medium-to-high level routers.

Finally, what about WDS, Wireless Distribution System?  It's present in the
GUI config for both versions of dd-wrt I have installed.  On the surface, this
would appear to be the exact solution that I am looking for.  Howeever... I
did a fair bit of reading before hand to see if I should use it and how to do
so.

In the *worst* case, WDS is not well specified in the standards, will only
work with routers from the same manufacturer (and often only the same models,
too), and is complete overkill for my needs.

In the *best* case scenario, WDS is much more friendly, and works among
hardware from various manufacturers.  The downside is that the encryption
settings WDS is compatible with are extremely limited, so mucn so that it
doesn't work with WPA2 Personal w/AES.  I suspect the reasoning behind this is
that anybody who is going to take the time to setup WDS is probably going to
also take the time to use something like RADIUS for security.

At any rate, the WDS documentation and info provided by users was spotty and
contradictory at best.

Not having gone the WDS route, I now have my two routers each providing a 2.4
and 5 GHz AP.  Their names are Bebop, BebopCola, MangoReinhardt, and
MarianMcPinapple.  And if you get that joke, congratulations, you've just won
the Internet.  :)


I hope this story and provided links helps others, even if a little.  In the
off chance I can answer any questions, just ask.


-- 
--John Gruenenfelder    Systems Manager, MKS Imaging Technology, LLC.
Try Weasel Reader for PalmOS  --  http://weaselreader.org
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