[AusNOG] Strange ADSL problem - troubleshooting / diagnosis advice wanted

[Beeson, Ayden]

I haven't yet, I don't have another handy but it'd be odd that it would start now, though maybe I have a line problem paired with a bug.

I have a bunch of really good test items to check, I'll monitor for a layer 1 problem for now and go from there while I wait for the ISP to do their thing.

Thanks to everybody for the awesome advice, I'll keep you posted :)

Thanks,
Ayden Beeson

From: AusNOG [mailto:ausnog-bounces at lists.ausnog.net] On Behalf Of Paul Brooks
Sent: Wednesday, 10 September 2014 2:40 PM
To: ausnog at lists.ausnog.net
Subject: Re: [AusNOG] Strange ADSL problem - troubleshooting / diagnosis advice wanted

On 10/09/2014 1:55 PM, Beeson, Ayden wrote:
I'll have another look at actual router level access from the WAN but I'd still see it in my netflow collection from that interface.

I'm 99.99% percent it isn't coming from me or even to me directly, I thought the same as you and did a lot of digging to double check.

I have both SNMP and Netflow monitoring and logging configured on the modem and neither show any significant activity during these time periods on either the up or the downstream.
It may be a re-training bug between your modem and the DSLAM. ADSL2+ is supposed to re-train to a new sync rate seamlessly without packet drops, whereas the older ADSL1 had to effectively drop the line, re-sync, generate a new bitfield table per tone to cope with changes to background noise and cross-talk that caused a need for a re-sync.
Perhaps there is a bug causing the DSLAM and the modem to become confused about the number of bits per tone, and which bits go in which DSL tone, on the transmission path. That would cause a very high bit-error-rate, causing packets to be dropped when checksums and fields come through corrupted.

Have you tried a different make/model DSL modem?

P.

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