[c-nsp] OK, what is a cheap and dirty hack to test a port

[Luan Nguyen]

Is it a Verizon circuit?
We have a T1 circuit with Verizon and have the same problem.  We have a
point to point circuit, so one side has clocking set to internal to provide
the clocking and the other side feeds from the line.
I wrote the problem up at http://ccie-security.blogspot.com/
But basically, it will be up for a some hours then down, then I call them to
test and it's good again.  Sometime it's good just by unplug the cable and
plug it back.  Like you, we changed everything and that didn't help. 
Finally, we talked to a knowledgeable Verizon tester and he mentioned the
rate on the line is ~17 which is high.  It should be around 0 or negative.
He said that's because of mismatch clocking between our hardware and the
central office crossover equipment. The normal tester won't look at this,
they only do the loopback pattern testing, so you should ask them about the
rate of your line.
They swapped one smart jack, but that didn't help, so they will swap the
other today.  Hopefully that will do it.
Good information here about troubleshooting T1
http://www.informit.com/library/content.aspx?b=Troubleshooting_Remote_Access
&seqNum=61


Luan Nguyen
Chesapeake NetCraftsmen, LLC.
www.NetCraftsmen.net


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Ted Mittelstaedt
Sent: Wednesday, October 15, 2008 7:31 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] OK, what is a cheap and dirty hack to test a port

Hi All,

  I have an 8 port PA-8T serial card in a router.  The card has an
octopus cable that is plugged into a rack of card DSU's.  Most
of the DSU's have T1's into them.

  One T1 has developed a problem where it runs for a few hours
and then the router serial interface it is on goes down.  When
it's down, from the carrier side the carrier can issue a loop
command to the CSU on the port, and the CSU will loop up, and
the carrier can run patterns on it all day long just fine.

  I have replaced both the 8 port card and the DSU card in the
rack on that specific port with no change.

  If I momentararily flip the loopback switch on the DSU to throw a loop
towards the carrier, facing away from the router, when the switch
returns the router port enables and the T1 runs for a few more
hours just fine.  I didn't believe this when I first saw it,
but I've done it several times since.  I actually don't think the
looping has anything to do with anything though - if I pull the
DSU card and replace it, the circuit comes back up also.

  So I went and moved the T1 to another DSU and port on the router and
inserted a physical loopback plug into the problem DSU network port.  The
router port of course sees this as a looped port now.

  My question, is there a way I can configure the router port
so that I can throw a massive amount of (bogus, naturally)
traffic to it, and the traffic will go out the port, through the
DSU, loopback through the hard loopback plug, then come back
into the router and go into the bit bucket?

 If I simply assign something like IP 127.0.0.5/30 to the port and
throw a ton of traffic to 127.0.0.6, will the packets actually
go out the port?  Or will the router see that the port is looped
and just discard the traffic?

Ted

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