[Gllug] Bridging from wired to wireless

damion.yates at gmail.com damion.yates at gmail.com
Sat Jun 18 12:35:11 UTC 2011

On Fri, 17 Jun 2011, Adrian McMenamin wrote:

> On Thu, June 16, 2011 10:30 pm, damion.yates at gmail.com wrote:
> > On Mon, 13 Jun 2011, Adrian McMenamin wrote:
> >
> > > This drove me mad all weekend and the time has come to admit that
> > > I and Google cannot solve it alone...
> > >
> > > I want to extend the range of my domestic wireless network by
> > > bridging between a wireless card and a wired card on a machine at
> > > one extremity of the ethernet.
> >
> > Just to be clear, you have an existing spare machine and want to
> > play with linux bridging?
> No. I want to (and have) extended the range of the wireless coverage
> of my existing wireless/wired network by bridging the ethernet
> connection of a machine in a corner of the house with poor wireless
> reception with a wireless card/AP I have inserted in a space PCI slot.
> It works.

Text only makes it difficult to express the tone of a comment.  I didn't
mean it to sound scathing like you were wasting your time.  I personally
have always wanted to play with the bridging support, years back when
compiling the kernel and seeing the kernel options and briefly glancing
at the supporting docs.

In fact a load of wifi options all became a lot easier at about kernel
2.6.32 when they finally tidied up all of the wifi stack and driver
interactions permitting things like Infrastructure support on any wifi
chipset that is capable, rather than a small minority that happened to
have the driver written to permit it.  This was a shockingly poor mess
before and you had a small limited set of h/ware that you needed to own
that would permit you to become an access point.  Even rudimentary
bridging support some 10+ years ago, started with chipset/driver
specific combinations.

So what I actually meant was, that I envied your spare time!  The only
reason I have time to write this lengthy email is because it's father's
day weekend and I've asked for a lie-in!

I'm actually a little annoyed with the constant improvements in
autoconfiguration, autodetection and general "It just works(tm)"
improvements that they keep putting in the Linux kernel.  I miss the old
days before I had kids, where I could spend hours tinkering and working
around limitations configuring systems so they worked the way I liked.
Xorg just works, random audio/wifi/etc drivers just work, how boring :)

The solution I propose below means a free (if you know somebody) or
~7quid from ebay (I just checked) wrt54g or similar, access point.
These are a VERY low power, silent MIPS based linux server with a wifi
chipset/driver that support bridging and Infrastructure support, the
kernel has all the bridging support compiled and configured and
typically these have ~4 100mb switch RJ45 ports for further wired
devices as well as their broadcasting A/G/N wifi powerfully around
themselves.  Some of them permit a shell so you can ssh/telnet in and
lsmod/cat around and see what it is they've configured if you do fancy
replicating it on a more stock linux box.
> > This is bad for the environment IMO.  Just plug a cheap/free (people
> > always have spare) wifi AP in.
> "bad for the environment"? As in the natural environment? Why is your
> solution better?

Heh, I'm far from green myself, this was a flippant way of explaining
that using a PC (or even laptop) rather than something lower power was
going to

- Cost more for your electricity bill
- generate noise
- generate heat
- eat your own time
- be less reliable (HDD etc)
- take more space

The 1st three being the worse for the environment part.  However, if you
already leave this PC on all the time anyway then yes this isn't really
going to improve anything.

As you have actually already sorted it then that's great, I'd be
interested in hearing what technique you used as there are a few I can
think of that should work:

- do it with routing - some client network edits may be needed, nat can
  work around that but is an awful solution.

- Clever use of proxy-arp and intentionally smaller (technically
  incorrect for your network) subnets meaning your PC forwards packets
  as needed despite being LAN wide on the same larger subnet.  (I think
  setting the same IP on both interfaces might be accidentally kludging
  this solution)

- enable full bridging support with no IP necessarily assigned to either
  (both) of the actual interfaces, this involves special kernel
  compiles/modules and configuration I've yet to play with.

> > I'm also considering simplifying it more with:
> >
> > http://www.devolo.co.uk/consumer/77_dlan-200-av-wireless-n_starter-kit_product-presentation_1.html?l=en

What do others think of this device?  It sounds awesome and Devolo
provide admin utilities for win/mac/linux which is very nice of them.  I
have the old 85Mb/sec original h/ware they produced, but am considering
upgrading, although I'm torn between the main filter/passthrough model
and this wifi one.

- Damion
Gllug mailing list  -  Gllug at gllug.org.uk

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