Re: configuring ppp and lan

richard@xxxxxxxxxxxxx wrote:
I'm finally beginning to have some internet here in the Appennine alps.
No land line so I have acquired a usb gsm modem. (To be truthful, I
still don't know if it will work at the house which also has no mobile
signal, but I have a directional antenna with a 10dB gain that may fix

To the point. Trying it out where there is a gsm signal, I have got ppp
running, but cannot configure the box with the modem so that both the
LAN and the PPP work at the same time.

Have you consulted any of the Debian networking Howtos? If not, that should
probably be your next step. All the Howtos can be installed as a deb package,
or else read on the web. For the purposes of this reply I will presume that you
have not completed, nor are aware of, the following (non-inclusive list of)
necessary steps. Sorry if that's not a correct assumption.

You need the ethernet bridging driver (and other related drivers) installed
in the kernel, 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).

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, or some
combination. On my LAN, my modem/gateway-router gets the DNS server's IP
address using DHCP, and serves DNS to my Debian gateway/firewall, which in
turn serves DNS to my LAN clients. This way I never have to configure
DNS server address on my gateway, and my LAN clients are all configured to
use the gateway's IP address, which never changes, for DNS.

If I 'poff', the lan sort of
works. If I 'ifdown eth1' (the wifi built into t he box), the ppp
connection resolves correctly. dhclient rewrites resolv.conf giving it
one of the nameservers of the provider (Wind), and the router/switch
address as the second nameserver. I'm not sure why. The router (D-Link
DI524) doesn't actualy seem to do any DNS (although it knows the
hostnames and IPs on the internal subnet), so that may be a part of the
problem, but the correct nameserver ought to be accessed at least some
of the time. dhclient also writes the routing table and maybe I have got
something wrong here. netstat -r gives

Destination Gateway Genmask Flags MSS Window irtt Iface
joiner.mulinoca * UH 0 0 0 ppp0
default * U 0 0 0 ppp0

when pppd is up. And when eth1 is up, it says

Destination Gateway Genmask Flags MSS Window irtt Iface * U 0 0 0 eth1
default UG 0 0 0 eth1

with both up I get

Destination Gateway Genmask Flags MSS Windo irtt
joiner.mulinoc * UH 0 0 0 ppp0 * U 0 0 0 eth1
default UG 0 0 0 eth1 is the box with both the modem and the lan
connection. the lan as you can see is 192.168.133.x and the modem local
address insists on being joiner has both addresses in
its /etc/hosts, which is I suppose the reason the name is shown in the
routing table rather than the IP allocated by

I feel even more confused now, so I hope this makes sense to somebody.
I wondered if I should reconfigure the whole lan to be on the same
subnet as the Wind modem, though I cannot see why that should be

Any ideas?

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