Last week, I subscribed to a new ISP (Free), to benefit from discounts as well as better hardware, gateway and set-top-box.

My new ISP and the incumbent operator were fast enough to take over my DSL line not even 2 days after my subscription. Though, Free did not bother sending the new equipment yet, I was left with the gateway from my previous ISP which was not connecting anymore.

To get back online, I had to pull out a few tricks I used to do a while back when I was at Mandriva with the only legacy modem I got: a green Speedtouch USB (nicknamed the "manta ray").

Unfortunately, the DrakX network tools that I used to maintain do not seem to work anymore with this modem and the quite unusual DSL connection using IP over ATM.

I had to install the speedtouch-firmware package, needed by the spedtch module, as well as linux-atm, providing the atmarp tools.

The modem was synchronizig fine, though about twice as slow as usual (this is an ADSL1 modem), according to the dmesg logs:

[14264369.849647] ATM dev 0: ADSL line is synchronising
[14264413.298572] ATM dev 0: DSL line goes up
[14264413.307430] ATM dev 0: ADSL line is up (7200 kb/s down | 896 kb/s up)

There are a few atmarp commands to run to configure IP over ATM:

# atmarpd -b -l syslog
# atmarp -c atm0
# ifconfig atm0 82.235.5.110 netmask 255.255.255.0 mtu 1500 up
# ip link set dev atm0 down
# ip link set dev atm0 up
# atmarp -s 82.235.5.254 8.36 null

And voila!

# ping 82.235.5.254
PING 82.235.5.254 (82.235.5.254) 56(84) bytes of data.
64 bytes from 82.235.5.254: icmp_seq=1 ttl=64 time=37.9 ms
# route add default gw 82.235.5.254

To avoid ATM fragmentation, we can configure the MTU to match a whole number of ATM cells (thanks Loïc!):

ifconfig atm0 mtu 1480

Finally, to use my PC as a gateway on my local network:

iptables -t nat -F POSTROUTING 
iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -j MASQUERADE

That's pretty old school, but I am back on the Internet! :-)