[c-nsp] PPP encapsulation triggering LOF on DS3?

[Vinny Abello]

That's interesting, as we have a DS3 with a certain provider running into a 
7206VXR PA-T3, etc.... and the provider said their default encapsulation 
type is PPP. We turned up the line and it looked ok and we could ping 
across it no problem... as soon as we turned up BGP and had traffic flowing 
over it, it seemed almost like certain traffic was being blocked but not 
all of it. After troubleshooting for quite some time, I suggested they 
enable scrambling on the circuit. Once scrambling was enabled, everything 
was pristine. We never tried HDLC as I don't think it would have made a 
difference, but that's interesting to hear. All of our clear channel DS3's 
on our network run with scrambling enabled (on our backbone and such). I 
believe one is HDLC actually, but most are PPP but they all have scrambling 
enabled. I've never had good experiences without scrambling enabled but it 
could just be my particular situations.

At 08:46 PM 11/18/2004, Kevin Graham wrote:
>Just ran into a problem that I'm absolutely clueless on that I was
>hoping someone could share some insight..
>
>On a clear-channel DS3 terminating directly onto Cisco DS3 interfaces
>on both ends (PA-T3 on a 7200 and some GSR LC on the other) w/ PPP
>encapsulation link that had been good for several months went down.
>Interface would bounce down and then back up every 20s or so with an
>rxLOF, though line proto would never go up with a pile of CRC's on the
>7200 side (GSR side was always up/down with no errors). clockrate was
>osillating some though always in the 44M range.
>
>Loopbacks either way all came back clean and telco PM also looked
>good. However, whenever the link was normalized, the troublesome
>behavior would come back. After a round of loopbacks (of course using
>HDLC), both ends noticed that the link was running perfectly. Going
>back to PPP would cause the same problems..Went ahead and left it at
>HDLC and has been running fine.
>
>So... Is anyone aware of WTF could be going on that would cause PPP
>encapsulation to trigger a consistent LOF condition whereas HDLC does
>not? The only thing that comes to mind at all is perhaps scrambling
>(which is disabled), though as mentioned the line has been stable for
>months....
>
>Thanks.
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Vinny Abello
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