bridging eth1 to eth0

[Matt Price]

On 12/29/06, Andrew Sackville-West <andrew at farwestbilliards.com> wrote:
> On Fri, Dec 29, 2006 at 04:42:49PM -0500, Matt Price wrote:
> > From:         Matt Price <matt.price at utoronto.ca>
> > To:   TLUG <tlug at ss.org>
> > Subject:      bridge eth1 to eth0?
> > Date:         Fri, 29 Dec 2006 15:51:31 -0500
> >
> >
> > hi,
> >
> > for stupid reasons I need to install via netboot on a compaq tablet
> > (hoping this will work, it's my last shot!).  I have an ubuntu desktop
> > with two ethernet cards, eth0 & eth1, and have set up dhcp & tftp on
> > eth1 as documented in various places on the web, e.g. here:
> >
> > http://www.debian-administration.org/articles/478
> >
> >
> > this works fine to a point.  I have the ubuntu edgy netboot images
> > in /var/lib/tftpboot, my tablet starts up with pxe, finding the images,
> > and is ready to install but cannot find the broader internet 0-- it
> > doesn't seem to see past the eth1 subnet.  So, probably a simple
> > question:  how  do I enable the eth1 traffic to bridge across to eth0
> > and thus access the whole internet?  I guess it has something to do with
> > ip forwarding or ip masquarading or one of those very scary and arcane
> > pieces of dark magic.
>
>
> yes its ip_forward. not scary or arcane. since you're behind a
> firewall, you may not have to do anything more than turn it on. not
> sure if it'll pass through back to you -- that may require ip
> masquerade. simple easy test:
>
> as root
>
> echo 1 > /proc/sys/net/ipv4/ip_forward
>
> and see what happens. that should immediately turn on ip forwarding.

Thanks Andrew.  I tried this to no effect (even rebooting to make sure
I wasn't missing a step somewhere).   in a small network like this:

WAN
 |
 |
 |
--------------------------------
| cheap linksys router |    192.168.2.1
--------------------------------
|                             |
|                             |
|   (DHCP CLIENT)   |(192.168.2.210, 192.168.0.1)              (DHCP client)
-----------                 -------------------
-----------------
laptop  |                | Desktop   | ------------------------|    Tablet    |
-----------                 -----------------
-----------------

>From the Desktop I can ping 192.168.2.1, www.google.com, or the
tablet's dhcp-assigned IP address.  From the laptop I can ping
192.168.2.1, www.google.com, but not 192.168.0.1 (I suppose that's not
really surprising).  From the tablet I can ping 192.168.0.1 but
nothing else.  It's the third part I care about obviously -- do I
really not need any more complex set up than turning on ip_forward?
If not, then I guessthere's something messed up in the set up for the
desktop's networking.  Howm ight I diagnose that?
Anyway thanks again,

Matt


>
> because you're already behind a router (firewall too?) you don't need
> any other bits so that may be enough.
>
> you should google on this subject a bit.
>
> A
>
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