Re: configuring ppp and lan

[richard@the-place.net]

On Mon, Nov 27, 2006 at 10:51:16PM -0500, Marty wrote:

> richard@the-place.net wrote:
[...]
> >No land line so I have acquired a usb gsm (gprs) modem.
>
> Have you consulted any of the Debian networking Howtos?
[...]
>
> You need the ethernet bridging driver (and other related drivers) installed
> in the kernel,
I decided not to compile a new kernel (I am not sufficiently expert),but
to see what can be done using my stock kernel (2.6.15-26-386).

> and you also have to configure iptables for packet routing, Network
> Address Translation/IP Masquerading (NAT) and (optionally)
> port-forwarding on your gateway machine.  You will have to configure
> other iptables networking features as well.  In particular you will
> need the firewall features, unless your router has very good firewall
> features (something I have not found in cheap routers).

I installed and tried to configure shorewall, recommended in another
thread here recently.  It is not as easy to do as it sounds, but the
manuals are good.  In the end, it was not a complete success, as the
ppp0 and eth1 interfaces cannot be used at once, and shorewall start
complains:
    Setting up Masquerading/SNAT...
       ERROR: Unable to determine the routes through interface "eth1"
    IP Forwarding Enabled
    /sbin/shorewall: line 524:  6064 Terminated   ${VARDIR}/.start
$debugging start

> For DNS you can use your gateway machine as the DNS server (again with
> iptables configured manually or using a program like dnsmasq), or you can
> use the router or your ISP's DNS servers for name resolution,

(trying to be brief...) The setup is like this:

                                                   usb
                  \  / -- --(wifi)-- -- BOX1------ gprs ) ) ) ) i'net
                   \/                              modem
  BOX2 --------- DLink
                 wireless
  BOX3 --------- router &
                 dhcpserver

In theory, the router should provide DNS for the local network.  They
never seem to (In London too I had to provide DNS server with bind9 on
one of the boxes with a NetGear adsl modem/firewall/dhcpserver/wifi AP).

I get no DNS service from the DLink, so I installed djbdns on BOX1.  It
is supposed to garner dhcp info and provide local network resolution,
but I could not understand how, and it doesn't.  In any case, dhclient
continues to write the DLink as the nameserver in resolv.conf.

To overcome the conflict between ppp0 and dhclient writing
/etc/resolv.conf and the routing table, I installed resolvconf.  This
neatly collects the wrong information from the dhclient and part of the
information from ppp0 and writes and updates a special
/etc/resolvconf/run/resolv.conf which is symlinked to /etc/resolv.conf.
The result is two namservers are listed, the second nameserver of the
ISP, and the DLink router.  I tried swapping the IP addresses of the
DLink and BOX1 to get BOX listed as DNS server, but dhclient/resolvconf
quickly adjusted the entry to point to the DLink.

At this point I have spent more time than I have available for this and
have to get a usable work-round.  Seeing that _any_ internet connection
is better than none, I shall accept the need to operate only ppp0 or
eth1 on BOX1 and BOX2 and BOX3 will just manage with no internet
connection.  To do this, I shall use the resolvconf package to divert
the misinformation from dhclient to its special file and remove the
symlink.  Then I shall use a pair of simple scrits to bring up eth1 or
ppp0, and copy the appropriate pre-made file to /etc/resolv.conf.  The
routing table is okay when only one interface is up.  A messy hack, but
better than nothing.

Thanks Marty and thanks too to Bill Marcum.

--
richard