ADSL, Proxy & Bridge

[Nigel Wade]

On Tuesday 26 Jul 2005 02:49, Jhon Ramawi Putra wrote:
> redhat-install-list-bounces at redhat.com wrote on 07/26/2005 12:45:52 AM:
> > Jhon Ramawi Putra wrote:
> > > Dear Gurus...
> > >
> > > May be this is a beginner question, but any help will be appreciated.
> > > This is existing my network diagram:
> > >
> > > (.....Internet.....) --- [ADSL MODEM]-----[LAN Switch] ---- Desktops
> > > (192.168.0.1, etc....)
> > >                       192.168.0.9
> > >
> > > The ADSL Modem act as gateway.
> > >
> > > Now i want to configure my network to be like this:
> > >
> > > (.....Internet.....) ---[ADSL MODEM]
> > >                 ip : 10.0.0.1, net mask : 255.0.0.0
> > >
> > >
> > >                 eth0: 10.0.0.2, net mask : 255.0.0.0
> > >                 [Computer A]
> > >                 eth1:192.168.0.10 netmask : 255.255.255.0
> > >
> > >
> > >                 [LAN Switch] ----  Desktops (192.168.0.1, etc ... with
> > >
> > > netmask : 255.255.255.0)
> > >
> > > The ADSL Modem is attached to Computer A via eth0. Then my eth1 is
> > > connected to LAN. I want to make Computer A as Proxy Server .
> > >
> > > Then i tried to make a  "bridge" using brctl, and followed every step
>
> in
>
> > > "How to" documents that i found from googling, but i got no success.
> > > Computer A can ping to LAN Clients dan Browse to Internet. LAN Clients
>
> can
>
> > > ping Computer A, but they can't ping The ADSL Modem and browse
>
> internet.
>
> > > So, i assumed that the bridge didn't working well.
> >
> > You need to enable IP forwarding in computer-a to make it act as a
> > router.  For that, either do this:
> >
> >    echo 1 >/proc/sys/net/ipv4/ip_forward
> >
> > or change the line in /etc/sysctl.conf that reads:
> >
> >    net.ipv4.ip_forward = 0
> >
> > to
> >
> >    net.ipv4.ip_forward = 1
> >
> > and either reboot or use "sysctl -w net.ipv4.ip_forward=1".  For proxy
> > operations, you should install and configure squid.
> > ----------------------------------------------------------------------
> > - Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
> > - VitalStream, Inc.                       http://www.vitalstream.com -
> > -                                                                    -
> > -    Admitting you have a problem is the first step toward getting   -
> > -    medicated for it.      -- Jim Evarts (http://www.TopFive.com)   -
> > ----------------------------------------------------------------------
> >
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>
> Thanks Rick,
>
> I did this:
> >    echo 1 >/proc/sys/net/ipv4/ip_forward
>
> but i didn't do this one:
> > and either reboot or use "sysctl -w net.ipv4.ip_forward=1".
>
> Before i configured the bridge, i assigned each NIC card with IP. Then i
> read this in
> http://www.faqs.org/docs/Linux-HOWTO/Ethernet-Bridge-netfilter-HOWTO.html
>
> "But now they became part of the logical bridge device and therefore need
> no IP configuration any longer"
>
> and another tutorial said that i should not assigned IP address first to
> the NICs card before configure the bridge nor set DHCP for it. So, may be
> that was my fault :)
>
> Ok, i'll try to set it up again (end of this week...). Thanks Rick....!
>
> Best Regards,
> Jhon Ramawi Putra
>

In your case you need Computer A to act as a router, not a bridge. A bridge 
sits between different segments of the *same* subnet, and provides a 
transparent link between the two. It may, or may not, have an IP address 
which is part of the same subnet.

In your case you have two different networks on either side of Computer A, 
10/8 on one side and 192.168.0/24 on the other side, so the machine needs to 
act as a router between these networks. Eth0 and eth1 are already setup to be 
part of each network, so all you need is to configure routing to route 
packets between eth0 and eth1 for these two networks.

-- 
Nigel Wade, System Administrator, Space Plasma Physics Group,
            University of Leicester, Leicester, LE1 7RH, UK 
E-mail :    nmw at ion.le.ac.uk 
Phone :     +44 (0)116 2523548, Fax : +44 (0)116 2523555