linux modem remote access server

Hello,

I have a remote monitoring setup. Normally it's connected to the
outside world via cable-modem (high speed internet connection). A
failure in the cable modem would be inconvenient (would require my
flying cross country to fix the problem). Therefore, I want to set up a
backup access method with a modem on a POTS (telephone) line.

The reason for this is redundancy. If the cable modem fails, I still
want a low-tech means of getting in and making sure the system is still
working.

I have a Linux machine on my network, and I'd like to connect one of
it's serial ports up to a modem, set the modem to auto-answer mode, and
run a serial console to that modem. That way I can dial-in and see
what's going on if the cable modem fails. I don't need anything fancy
like a PPP or SLIP connection. Just a dial-in login is fine.

Is there a FAQ anywhere on setting this sort of thing up? In
particular, I want to make sure I don't introduce a big security hole
in my network. I'm assuming that as long as all of the logins on the
machine are secured with reasonable passwords that the machine would be
secure?

Also, any instructions on how to configure the modem would be helpful.
I'm assuming that it either has dipswitches or nvram configuration that
can put it into auto-answer mode.

Thanks,
Scott

"Scott" <(E-Mail Removed)> écrivait news:1129395439.676268.260630
@f14g2000cwb.googlegroups.com:
> Is there a FAQ anywhere on setting this sort of thing up? In
> particular, I want to make sure I don't introduce a big security hole
> in my network. I'm assuming that as long as all of the logins on the
> machine are secured with reasonable passwords that the machine would be
> secure?

For the FAQ, look at in the HOW-TO section at the Linux Documentation
Project (LDTP is a good start point for Linux Documentation)

http://www.tldp.org

A good password, program generated is always a good idea. You may add a
"strong" security by using a call-back connexion. In a such case, you
ring the modem and the modem call back a fix phone number on your side.
In that case auto-answer is disabled.

"Old" great modem like the USR Courier Modem can directly do that without
any OS configuration.

However, Linux can do it with a proper scripts (searh at the LDP)

> Also, any instructions on how to configure the modem would be helpful.
> I'm assuming that it either has dipswitches or nvram configuration that
> can put it into auto-answer mode.

"Classic" modem use the AT (also named HAYES) command, that you send to
the modem using a serial terminal (e.g.: minicom).

You must have the AT commands table of the modem.


Regards

Antoine EMERIT wrote:
> "Scott" <(E-Mail Removed)> écrivait news:1129395439.676268.260630
> @f14g2000cwb.googlegroups.com:
>
>>Is there a FAQ anywhere on setting this sort of thing up? In
>>particular, I want to make sure I don't introduce a big security hole
>>in my network. I'm assuming that as long as all of the logins on the
>>machine are secured with reasonable passwords that the machine would be
>>secure?
>
>
> For the FAQ, look at in the HOW-TO section at the Linux Documentation
> Project (LDTP is a good start point for Linux Documentation)
>
> http://www.tldp.org


Probably the best to start with is Modem-HOWTO. The HOWTO is quite fresh
(June 2005). The section 3 handles modem pools and RAS.

--

Tauno Voipio
tauno voipio (at) iki fi

Scott wrote:

> I have a remote monitoring setup. Normally it's connected to the
> outside world via cable-modem (high speed internet connection). A
> failure in the cable modem would be inconvenient (would require my
> flying cross country to fix the problem). Therefore, I want to set up a
> backup access method with a modem on a POTS (telephone) line.

There's a mini ISP howto at the Linux Documentation Project site. It's for
Red Hat and a few years old, but it should give you some ideas.

Scott <(E-Mail Removed)> wrote:
> Hello,

> I have a remote monitoring setup. Normally it's connected to the
> outside world via cable-modem (high speed internet connection). A
> failure in the cable modem would be inconvenient (would require my
> flying cross country to fix the problem). Therefore, I want to set up a
> backup access method with a modem on a POTS (telephone) line.

> The reason for this is redundancy. If the cable modem fails, I still
> want a low-tech means of getting in and making sure the system is still
> working.

> I have a Linux machine on my network, and I'd like to connect one of
> it's serial ports up to a modem, set the modem to auto-answer mode, and
> run a serial console to that modem. That way I can dial-in and see
> what's going on if the cable modem fails. I don't need anything fancy
> like a PPP or SLIP connection. Just a dial-in login is fine.

ftp://alpha.greenie.net/pub/mgetty/s...3-Apr10.tar.gz

> Is there a FAQ anywhere on setting this sort of thing up? In
> particular, I want to make sure I don't introduce a big security hole
> in my network. I'm assuming that as long as all of the logins on the
> machine are secured with reasonable passwords that the machine would be
> secure?

Search for "mgetty" at http://tldp.org to find FAQs and HOWTOs.

As for logins, IMHO direct logins over a landline using a modem are
reasonably secure.

> Also, any instructions on how to configure the modem would be helpful.
> I'm assuming that it either has dipswitches or nvram configuration that
> can put it into auto-answer mode.

Mgetty can be configured to answer by sending ATA to the modem on
detection of one or more RINGs (default 1 RING, more than one is
specified by -n N on the mgetty command line where N is the number
of rings - search for -n in "info mgetty" for more details).

If Caller ID is available then it can also be configured to only
answer specified caller numbers. Mgetty can be also configured to
answer a call using the "ringback" and "ringback-time SEC" features
(which can be combined by using -R SEC on the mgetty command line -
search for ringback and -R in "info mgetty" for more details).

-- Clifford Kite Email: "echo xvgr_yvahk-(E-Mail Removed)|rot13"
PPP-Q&A links, downloads: http://ckite.no-ip.net/
/* "PPPoE has many advantages for DSL service providers, and
practically none for DSL consumers."
- David F. Skoll */