Re: What is going on with my Dialup?

On Wed, 16 Jul 2008, in the Usenet newsgroup comp.os.linux.networking, in
article <KY2dnepobYPlL-PVnZ2dnUVZ_gednZ2d@xxxxxxx>, Tom Wyley wrote:

So for now I am stuck on a rural dial up line that somehow the phone
company has limited to about 26k throughput. I am trying to find out
from the telco what is going on and why not 56k, but for now I am
watching the lights on an external modem and they are revealing some
stuff that I don't like.

1. Are you using the "correct" init-string according to the manufacturer
of your un-named modem?
2. "rural dial up" suggests you are some distance from town - how noisy
is the phone line? 56K (and indeed anything over about 26K tends to
want to see a "clean" phone line - 26-33.6K is almost harder than 37-56K
on a noisier line.
3. Looking at modem lights isn't as informative as looking at the actual
data transfers.

I am not much of a telecommunications guru (read: not at all) but it
would appear that most of the traffic on my link is not mine.

You're possibly seeing windoze "messenger spam" (UDP to ports 1025-1035)
but that should be relatively light. OTHER THAN THAT, your connection
is a point-to-point link, and the only traffic on that link is to/from
your computer.

I realize that there is a certain amount of handshaking on initial
connect, and some may be Firefox looking for updates (although I have
turned off all of that I can find). But there is a lot left over that
I can't explain.

Let's start by not using a browser. Most browsers are happy to try to
load every piece of eye-candy and other crap. What traffic do you see
when the browser isn't running?

Next I logged off and dialed back in with no browser at all. I should
have just talked to the ISP hardware and then dropped into a passive mode
with an occasional keep alive blip. But sure enough, in about 20 seconds
in comes a 3 minute continuous receive.

Figure out where the command line is, and run 'netstat -anptu' and see
what is talking to what. See the man page for netstat so you understand
what it's telling you.

The above post indicates two problems. Something is stealing a bunch of
what little bandwidth I have, and (I think) somebody is talking to me
unasked. This would never be noticed on a broadband link unless someone
was running some kind of trace.

Depending on what all you installed, there shouldn't be that much open
for "others" to connect to you. Nearly all of that traffic is _probably_
due to client things you are running - but you won't know that until
you find out what the traffic is. Most people install all kinds of
extra trash that they think might be interesting, and don't know what
it's actually doing.

What is the easist way to determine what is incoming on an Internet
connection?

[compton ~]$ netstat -anptu
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 8972/sshd
[compton ~]$

Doesn't really tell you, but the firewall is only accepting connections
from two ranges totalling 1500 addresses (a /22 and two /24s).

I know that I could learn Snort or such like, but I am just starting my
first career and there isn't a whole lot of time left for playing.

-rw-rw-r-- 1 gferg ldp 155096 Jan 23 2004 Security-HOWTO
-rw-rw-r-- 1 gferg ldp 278012 Jul 23 2002 Security-Quickstart-HOWTO

Should be on your system in /usr/share/HOWTO (or use your favorite search
engine) - and there are a number of other good ones.

Old guy
.

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