[X-Unix] Need to log internet connectivity

[William H. Magill]

On 27 Jun, 2004, at 09:18, Jerry Krinock wrote:

> Our DSL line is intermittent; it goes up and down over periods of 
> minutes
> and hours.  To troubleshoot local interference I need to run some 
> days-long
> experiments and get a log which would give me something like:
>
> 6:04 AM  DSL went down
> 6:10 AM  DSL came up
> 7:15 AM  DSL went down
> 7:22 AM  DSL came up
> ...
>
> What's the *easy* way to get this?

There is nothing inherent in the OS which will give you the 
information... especially since the definition of "up" and "down" is 
"relative."

For example, the DSL modem may in fact be up, but the DSLAM is down.
Or the Modem and DSLAM may both be functional, but the MAN behind it in 
never-never land.
Or the Modem, DSLAM and MAN may be functional but the WAN is 
unreachable.

[The MAN (metropolitan area network) is the ATM (asynchronous transfer 
mode) Cloud between my local Central Office and the ISP's Central 
Office. It is NOT a routed TCP/IP connection, but rather a classic 
Phone Company Circuit between two central offices -- your configuration 
may differ.]
[DSLAM = Digital Subscriber Loop Access Module -- a piece of equipment 
in the CO - Telco Central Office -- which separates the data and voice 
streams.]

In my case, with my DSL line I have a real ISP and static addresses, 
don't have to use PPPOE and DHCP. I have a script which runs 
periodically on one of my systems which uses ping to determine if 
certain portions of the network are reachable. So, I can tell if the 
MAN is down because I can't reach my ISP's router. I can tell if the 
WAN is down because I can't reach certain servers beyond my ISP's 
router.

I have had DSL since the beginning, so I have a seriously dumb and 
non-manageable DSL modem. If I had a "modern" DSL modem, I would be 
able to query it to determine if there was "sync" (and therefore a 
working circuit) between the DSL modem and the DSLAM, as well as an 
assortment of traffic counters. Most "modern" DSL modems, I think, 
respond to SNMP, and a number of them are "web addressable."

The only "trick" with such scripts is their period. Too frequent, and 
you load the connection with lots of non-productive and unnecessary 
traffic. Too infrequent and you miss what is the normal DSL "dropout" 
problem -- the 2 minute outage. Similarly, this "granularity of 
polling" determines how long (or short) the minimum outage will be.

[I use a 10 minute polling interval, which shortens itself if an outage 
is detected to 2 minutes until the outage clears.]

As far as troubleshooting interference on the DSL line, the most likely 
problem has to do with the modem loosing sync with the DSLAM. The cause 
is one of two things -- either you have real "line noise" problem; or 
you have CO activity which results in the DSLAM being reset on a 
"routine" basis by Telco technicians.

If you have an active phone line and are using "dongels" instead of a 
single splitter, they can be a source of "local" line noise, especially 
if devices are plugged into the phone line without a "dongel."

I've had DSL now for ?7+ years (it seems like forever), ever since it 
became available in my CO. Problems are rare now, but there was a 
definite learning curve in the beginning as the Telco technicians 
learned how the equipment worked, and especially, as there was a lot of 
active "coming and going" of new customers. Now, it works with zero 
outage for months at a time... then suddenly it will go nuts for a day 
or two, or maybe a week before it settles down again to no-outage 
activity.

T.T.F.N.
William H. Magill
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