FTTH Tiscali without modem

This is a short guide on how to connect your Linux box to the Internet using directly the GPON provided by Tiscali.

TL;DR

You just need pppd and a virtual Ethernet device. The latter is created with:

ip link add link eth0 name eth0.835 type vlan id 835

assuming your ethernet device is eth0.

Credentials for PPPoE can be obtained here for Tiscali. You can also sniff the CHAP authentication and crack it, the password is just 6 numeric characters.

To connect to the PPPoE server, install pppd and configure it

/etc/ppp/peers/tiscali

plugin pppoe.so
# rp_pppoe_ac 'your ac name'
# rp_pppoe_service 'your service name'

# network interface
eth0.835
# login name
name "NAME.SURNAME@tiscali.it"
usepeerdns
persist
# Uncomment this if you want to enable dial on demand
#demand
#idle 180
defaultroute
hide-password
noauth

and

/etc/ppp/chap-secrets

# Secrets for authentication using CHAP
# client                        server  secret                  IP addresses
"NAME.SURNAME@tiscali.it"       *       "123456"

(replace 123456 with your password)

Finally you can switch on the service with:

ppp call tiscali

and then use journalctl -f to check whether things are going fine.

Systemd automation can be created with the help of these scripts.

Long Story

The FFTH service comes with a GPON (gigabit-capable passive optical network), and I wanted to connect the PC with my self hosted services directly to its ethernet port, bypassing the big black box (ZTE H388X a.k.a. ZTE Modem Tim Hub+) customized with some mysterious proprietary firmware from TISCALI (I asked, of course they don't share it).

Needless to say, using the credentials that TISCALI gave me directly with pppd on my ethernet interface did not work. The logs and the error messages are

pppd[1336]: Plugin pppoe.so loaded.
pppd[1336]: PPPoE plugin from pppd 2.4.9
pppd[1337]: pppd 2.4.9 started by pie, uid 0
kernel: NET: Registered PF_PPPOX protocol family
pppd[1337]: Timeout waiting for PADO packets
pppd[1337]: Unable to complete PPPoE Discovery

For some reason, nobody replied with an Offer (PADO) to my request for a PPP Initiation (PADI). Not much gained from the error message, so the only way to find how to talk to the PPPoE server is to collect a working setup.

I managed to sniff the traffic between the modem and the GPON with this fantastic Ethernet Hub from the 90s!

The approach is like this:

The packets captured just after powering on the ZTE H388X are shown here:

There are basically three steps:

Red box: a termination request. Probably to clean up everything before starting a new session.
Yellow box: the PPP Initialization starts from the ZTE and is followed by an Offer from the Cisco server.
Green box: the authentication, with CHAP protocol.

When using pppd, the cleanup part is missing and the first packet is a PADI, which looks exactly like the one in packet No. 7 above, except for the 802.1Q part shown by the blue arrow. That was indeed the trick: the server replies only when the PADI request comes from a VLAN with ID 835.

Creating the vlan with

`ip link add link eth0 name eth0.835 type vlan id 835`

and setting it as the device for the PPP connection makes the Cisco server happy: it promptly replies to our PADI packet and the connection is setup in less than a second.