F200 ADSL USB Modem setup under GNU/Linux (Forthnet)

Copyright (c) 2007 Dimitri Marinakis.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".


This is a brief how-to and pointers for setting up the “Crypto F200” DSL modem, included in ADSL packs by the specific provider (Forthnet). The modem is used in the PPPoA mode (Point-to-Point Protocol over ATM). This DSL modem is made by Conexant and sold under many commercial names. It is directly supported by Linux kernels 2.6.10 and newer. Patches are available for older kernels.

An example script is provided for manual link activation (usable in firewall/router boxes). SuSE/openSuSE set-up instructions are also provided.

Update (15-Jun-2007) – I was brought to my attention that PPPoE (Point-to-Point Protocol over Ethernet) is also in use by Forthnet. In some cases it can be used as a work-around for the “77.49.xx.xxdomain problem (alternate domain is automagically selected). The 77.49.xx.xx domain was allocated to Forthnet in August 2006 and it may still be in the bogon lists of routers/firewalls, preventing access to various sites . See the companion note http://tlgu.carmen.gr/gnulinuxtips/Sagem F@st 800 E4 ADSL USB Modem setup - Otenet under GNU-Linux.html for PPPoE setup (in brief: the br2684 driver module is loaded, nas0 interface is created, nas0 interface is brought up, br2684ctl is used to control the interface, pppd is used to call the provider using the rp-pppoe.so module.


ADSL/DSL: Asymmetric / Digital Subscriber Link – (Asymmetric means that the receive/downlink and transmit/uplink speeds are different)

ATM: Asynchronous Transfer Mode – a connection oriented protocol using fixed-size cells, 53 bytes long.

ISDN: Integrated Services Digital Network

PPPoA: Point-to-Point Protocol over ATM

PPPoE: Point-to-Point Protocol over Ethernet


18-Jun-2007 – 77.49.xx.xx mystery solved
15-Jun-2007 – PPPoE pointer
04-Feb-2007 – First release – tlgu.carmen.gr



Information specific to this application

See also


The usual disclaimer about misconfiguring your system beyond repair or oblueterating your work applies: Don't blame it on me. Do one thing at a time. Read and Learn. Write to tlgu, carmen gr, in case this document contains inaccuracies, errors or if you have some information that others can benefit from.

Modem identification

> lsusb

Bus 001 Device 003: ID 0572:cb00 Conexant Systems (Rockwell), Inc. E-Tech ADSL Modem v2

This modem is based on the CONEXANT AccessRunner CX82320-21 ARM processor. The modem's application code (firmware) must be downloaded to the device, at which point it is supported by the cxacru (Conexant Access Runner) driver.

Modem firmware extraction

The modem firmware is included in the CD-ROM which accompanies the modem, in the file driver/Wan/CnxEtU.sys or driver/Lan/CnxEtU.sys and must be extracted and made available to the operating system for download to the modem. The two files are identical, 646784 bytes, Sep 12 2003, md5sum 28775c3f6df8c1f364f67d7121191000; similar-named files available for download may not work with the extractor.

The extractor is called cxacru-fw and is available at http://accessrunner.cvs.sourceforge.net/accessrunner/utils/

Download the file and compile to get the executable:

> gcc cxacru-fw.c -o cxacru-fw

Feed the file containing the driver to the extractor; the output file must be named cxacru-fw.bin and placed in the appropriate directory (/lib/firmware). So, assuming that you have copied the file from the CD-ROM to your working directory:

> ./cxacru-fw  CnxEtU.sys cxacru-fw.bin
> cp cxacru-fw.bin /lib/firmware

Now as soon as the modem is plugged-in and detected by the operating system, the firmware will be automagically downloaded.

Modem wiring

An “ADSL splitter” was included in the package. The telephone line is connected to the port marked “LINE”, the modem is connected to the port marked “MODEM” and the original network termination unit (typically an INTRACOM netmod for ISDN in this part of the world) is connect to the port marked “PHONE”.

Modem configuration

A configuration file is needed to match the modem's behavior to what is expected by the provider. PPP over ATM is the selected protocol, while we need to match the Virtual Path Identifier (VPI) and Virtual Circuit Identifier (VCI); these variables identify the next destination of an ATM cell.

# -------------- /etc/cxacru --------------------------------
# Config file for Conexant AccessRunner

# Driver mode
DRIVER_MODE=1 # 1 = normal, 2 = debug, 3 = normal+max speed (without ask adsl status), 4 = debug+max speed (without ask adsl status)

# Protocol
PROTOCOL_MODE=2 # 1 = RFC1483/2684 routed, 2 = PPP over ATM (pppoa), 3 = RFC1483/2684 bridged, 4 = PPP over Ethernet (pppoe)

# Paths

# if OPEN_MODE is blank then cxload uses default mode acoording VID & PID
# Values for OPEN_MODE are:
# 0 = auto selection, G.Handshake
# 1 = auto selection, T1.413
# 2 = G.Handshake
# 3 = ANSI T1.413
# 4 = ITU-T G.992.1 (G.DMT)
# 5 = ITU-T G.992.2 (G.LITE)


# Specific for RFC1483/2684 routed/bridged
# if IP_ADDRESS is blank in bridged mode then it uses DHCP to get IP
#---------------------------- end of /etc/cxacru ---------------------

Modem firmware download

Plug in the modem to an available USB port. The modem will be detected and control passed over to the cxacru driver. The modem light will start flashing and then it will light steadily (about 40 seconds).

Following is the relevant output from dmesg (or tail /var/log/messages):

usb 1-2: new full speed USB device using uhci_hcd and address 4
cxacru 1-2:1.0: found firmware cxacru-fw.bin
cxacru 1-2:1.0: ADSL line: attemtping to activate [ attemt ping ;-) ]
cxacru 1-2:1.0: ADSL line: down
cxacru 1-2:1.0: ADSL line: attemtping to activate
cxacru 1-2:1.0: ADSL line: training
cxacru 1-2:1.0: ADSL line: channel analysis
cxacru 1-2:1.0: ADSL line: up (768 kb/s down | 192 kb/s up)

The modem is now ready for operation. You need to activate it by running the Point-to-Point Protocol Daemon (pppd) using a console or through a graphics application (e.g. kinternet).

DSL setup

(skip to next section for SuSE setup using YaST and kinternet)

To establish a connection the point-to-point protocol daemon (pppd) is called, with the appropriate options. The options can be passed directly to pppd or read from a number of places: ~/.ppprc, /etc/ppp/options, /etc/ppp/peers/xxxx. In this example, options are read from a file in /etc/peers, called pppoa-forthnet. It is important to note that pppd will go through all relevant files to complete its options. In order to make sure that the proper options are selected use dump or dryrun (and read the man page).

The command to invoke the daemon is

> pppd call pppoa-forthnet

And the command to properly stop the daemon is

> kill -15 <pppd pid> (SIGTERM – see man 8 pppd)

(or CTRL/C if the daemon is still attached to a terminal – see example below)

When the daemon is invoked it will go through /etc/ppp/peers/pppoa-forthnet and, given the chance, through /etc/ppp/options to look for its options. The pppoa-forthnet script will establish a PPPoA connection for user username.ath.forthnet.gr@forthnet.gr through 8.35 (VPI.VCI). The authentication method used is PAP (Password Authentication Protocol), which means that the password must be entered in the /etc/ppp/pap-secrets file.

For other systems using CHAP (Challenge Handshake Authentication Protocol), the password must be entered in the /etc/ppp/chap-secrets file, in the same manner. Also, compression negotiation may be disabled if it is not supported by the service provider's server (there are several compression options).

The IP address will be determined by the provider's server. The link will not disconnect and, in case of disconnection, will try to reconnect. The Maximum Transfer Unit (MTU) to be negotiated is set at maximum - 16384 bytes (will most probably be negotiated down to 1500 bytes).

The connection, originally ppp0, will be renamed to dsl0 to distinguish it from the analog/ISDN modem connection which can serve as a backup under unusual circumstances (like waiting for the PTT network experts to perform the inevitable reset).

As soon as the connection is initiated, the provider's Domain Name Servers (DNS) will be entered in /etc/ppp/resolv.conf

Following are the necessary /etc/ppp/pap-secrets and /etc/ppp/peers/pppoa-forthnet scripts. Modify as necessary for your application.

#---------------------------- /etc/ppp/pap-secrets ---------------------
#hostname       *       password
username.ath.forthnet.gr@forthnet.gr * password
#---------------------------- end of /etc/ppp/pap-secrets ---------------

#----------------------- /etc/ppp/peers/pppoa-forthnet ------------------
# 070201 dm

# Uncomment dump option to see where the options are read from
# and how the connection progresses

# Use this name to look for a password in the secrets files
# User name for peer authentication (if different from name)
user username.ath.forthnet.gr@forthnet.gr

# (Reference only, do not use)
# SuSE uses passwordfd n (password file descriptor) to pass the password
#plugin passwordfd.so

# Look in /usr/lib/pppd/<pppd version e.g. 2.4.3>/ for pppoatm.so plugin
plugin pppoatm.so

# Add default route to the system routing tables using the peer as gateway

# Local IP address to be supplied by the peer

# Disable address/control compression
# Disable protocol field compression
# Disable  CCP  (Compression  Control Protocol) negotiation
# Disable Van Jacobson style TCP/IP header compression

# Do not disconnect if idle
idle 0

# Seconds to wait before re-initiating the link
holdoff 4

# Try to reopen the connection if it is terminated

# If it fails many times, however, terminate for good (0 is no limit, default 10)
maxfail 20

# Request up to 2 Domain Name Server addresses
# These will be passed to /etc/ppp/ip-up script as DNS1 and DNS2 and USEPEERDNS will be set to 1
# An /etc/ppp/resolv.conf file will be created with one or two name server addresses

# Attempt to initiate connection, wait for LCP packet if no reply

# Send LCP echo-request every n seconds to verify connection
lcp-echo-interval 5

# If n LCP echo-requests are sent without a valid LCP echo-reply, peer is dead
lcp-echo-failure 7

# Do not escape any control characters (for peer)
asyncmap 0

# Detach (or not) from the controlling terminal in case of successful connection

# Don't use IPX protocols

# New name for ppp0
ifname dsl0

# Specify maximum sizes for MTU/MRU (despite the fact that it will eventually settle to 1500)
mtu 16384
mru 16384

#----------------------- end of /etc/ppp/peers/pppoa-forthnet -----------

Example run with the dump option. Note that /etc/ppp/ip-up and /etc/ppp/ip-down scripts are called on connection establishment and termination:

> pppd call pppoa-forthnet

Plugin pppoatm.so loaded.
PPPoATM plugin_init
PPPoATM setdevname_pppoatm - SUCCESS:8.35
pppd options in effect:
nodetach                # (from /etc/ppp/peers/pppoa-forthnet)
holdoff 4               # (from /etc/ppp/peers/pppoa-forthnet)
idle 0          # (from /etc/ppp/peers/pppoa-forthnet)
persist         # (from /etc/ppp/peers/pppoa-forthnet)
maxfail 20              # (from /etc/ppp/peers/pppoa-forthnet)
ifname dsl0             # (from /etc/ppp/peers/pppoa-forthnet)
dump            # (from /etc/ppp/peers/pppoa-forthnet)
plugin pppoatm.so               # (from /etc/ppp/peers/pppoa-forthnet)
active-filter xxx # [don't know how to print value]             # (from /etc/ppp/filters)
noauth          # (from /etc/ppp/options)
name cathm.ath.forthnet.gr@forthnet.gr          # (from /etc/ppp/peers/pppoa-forthnet)
8.35            # (from /etc/ppp/peers/pppoa-forthnet)
8.35            # (from /etc/ppp/peers/pppoa-forthnet)
asyncmap 0              # (from /etc/ppp/peers/pppoa-forthnet)
mru 16384               # (from /etc/ppp/peers/pppoa-forthnet)
mtu 16384               # (from /etc/ppp/peers/pppoa-forthnet)
passive         # (from /etc/ppp/peers/pppoa-forthnet)
lcp-echo-failure 7              # (from /etc/ppp/peers/pppoa-forthnet)
lcp-echo-interval 5             # (from /etc/ppp/peers/pppoa-forthnet)
lcp-restart 2           # (from /etc/ppp/options)
lcp-max-configure 60            # (from /etc/ppp/options)
noipdefault             # (from /etc/ppp/peers/pppoa-forthnet)
defaultroute            # (from /etc/ppp/peers/pppoa-forthnet)
usepeerdns              # (from /etc/ppp/peers/pppoa-forthnet)
noipx           # (from /etc/ppp/peers/pppoa-forthnet)
Renamed interface ppp0 to dsl0
Using interface dsl0
Connect: dsl0 <--> 8.35
PAP authentication succeeded
local  IP address
remote IP address
primary   DNS address
secondary DNS address
Script /etc/ppp/ip-up finished (pid 23163), status = 0x0

[ifconfig at this point (on another terminal) will provide connection-specific information]

<CTRL/C> entered at the terminal where pppd is attached

Terminating on signal 2
Connect time 0.1 minutes.
Sent 0 bytes, received 904 bytes.
Connection terminated.
Script /etc/ppp/ip-down finished (pid 23314), status = 0x0

DSL setup using SuSE's YaST and kinternet

The SuSE/openSuSE GNU/Linux distribution's YaST (Yet another Setup Tool) can be used to set up the DSL connection, as follows:

Select Network Devices -> DSL. There are two tabs: DSL Devices and Providers.

Under the DSL Devices tab, click on Add. In the DSL Configuration window select PPP Mode (PPP over ATM) from the drop-down list, enter the VPI/VCI (8.35) – dot notation, don't use a slash...– and select the device activation method (Device Activation: Manually, User Controlled). Click on Next to select the provider.

In the Select Internet Service Provider (ISP) window, click on Custom Providers, New and give the Provider Name (e.g. forthnet_dsl), User Name (e.g. username.ath.forthnet.gr@forthnet.gr) and Password. Click on Next and select Modify DNS When Connected, Automatically Retrieve DNS and External Firewall Interface. Set Idle Time-Out to the desired value (600).

Now you can use kinternet to start and terminate the connection (Right click on the kinternet icon, View Log...). In our example the connection will be terminated automatically after 600 seconds of inactivity have passed.

> accounting 

(on a terminal) will provide an account your connections.

For the curious, SuSE initiates the connection it as follows (use ps aux | grep ppp to get the pppd process id and cat /proc/<pppd pid>/cmdline to verify):

As soon as you click on the kinternet icon the following two commands will be issued:

> /usr/sbin/smpppd-ifcfg --ifcfg=ifcfg-dsl0 --provider=providerx --user=xxxxxxx

> /usr/sbin/pppd  [options are placed on separate lines for perusal]

# Log messages are sent to file descriptor n
logfd 9 
call pppoatm 

# Maximum Transmit Unit bytes (9178 is the default PPP over ATM default)
mtu 1500 

# Maximum Receive Unit bytes
mru 1500 

# Allowed to accept different local and remote addresses

# Disconnect if idle for n seconds
idle 600 

# Peer is used as the gateway (route removed when PPP connection is broken)

# Replace existing default route with new default route

# Don't detach from controlling terminal

# Try to get the name server addresses from the ISP.

# Set the interface name (default is ppp0)
ifname dsl0

# Provide a parameter (or two?) to the ip-up and ip-down scripts
ipparam 'ifcfg-dsl0' 'providerx' 

# User name for authentication
user xxxxxxx.ath.forthnet.gr@forthnet.gr 
passwordfd 10 

Notice that logging is piped to file descriptor 9 and that the password will be read from file descriptor 10 (another way of providing the password to pppd). If you take a look at the log file, however, you will notice the following disconcerting diagnostic:

pppd[0]: Couldn't increase MTU to 9178

Nothing to worry about, really. Apparently, 9178 is the default MTU for PPP over ATM connections. Entering the maximum MTU parameter for negotiation in the relevant SuSE configuration file will rid of this statement (the MTU will still be 1500, though).

NAME='DSL Connection'

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If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.


Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.


You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.


The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.

    <one line to give the program's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    GNU General Public License for more details.
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

    Gnomovision version 69, Copyright (C) year name of author
    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:

  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
  `Gnomovision' (which makes passes at compilers) written by James Hacker.

  <signature of Ty Coon>, 1 April 1989
  Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.