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

Wed Sep 10 13:46:13 EST 2014

Have you requested an IP Address change (If Static), it sounds like someone is pushing some traffic towards your WAN and flooding the connection.

Alternatively you have an impacted machine being used as part of a botnet and it is smashing your upstream pipe.

Kindest Regards,
Nathan Brookfield

Chief Executive Officer
Simtronic Technologies Pty Ltd

Web: http://simtronic.com.au
Phone: 1300 592 330
Fax: (02) 4749 4950

On 10 Sep 2014, at 13:24, "Beeson, Ayden" <ABeeson at csu.edu.au<mailto:ABeeson at csu.edu.au>> wrote:

Hey everybody,

Firstly let me start by saying - This is a residential ADSL question, but I'm asking on the list as I'm looking for some specific DSL troubleshooting tips I may not be aware of / a better understanding of the network from the DSLAM onwards. I hope this email is not considered inappropriate for the list, I have lodged it with my ISP already (Exetel, via a Telstra wholesale ADSL2+ DSLAM connection) but I have a feeling given the strangeness of this one I'm in for a bit of a tough time to get it fixed. I'm not here to harass my ISP who may or may not have people on this list, nor beg for assistance etc, this is more of a general "here's a weird one, anybody got any thoughts?" kind of deal.

With that said, onto the problem and questions:

The problem:
Most nights (and potentially during the day, I'm not sure as I'm not at home to see it) my internet connection is working fine (I sync at around 16-17 mbit, so pretty decent) when all of a sudden my connection becomes almost unusable. It presents like congestion, but far more severe and almost instantly, with most TCP applications completely failing to work (i.e. can't load even my ISP's homepage due to connection timeouts) and UDP applications working very poorly, often only receiving data in occasional bursts every 10-30 seconds.

Voice communications (TeamSpeak in this case) work poorly but do get consistent data through, though the jitter makes it unusable and it often drops out too.

The connection goes from 100% fine to 1% functional in the space of about 2-5 seconds, but then stays like that for anywhere between 1 - 10 minutes.

So far I have done the basic things, check my modem, attenuation, ping checks, traceroutes etc. I have also confirmed my network is not using the link (both my SNMP and netflow from my modem indicate I'm using very little to 0 data before and during the "event") and the traceroutes look the same both when its fine and when its broken (other than the dropped packets and failed timed out lookups when its broken), the one thing I have noticed consistently is that the latency between my modem and the next L3 hop goes from a normal 29ms to 60ms.

The traceroutes or pings to www.exetel.com.au<http://www.exetel.com.au> (figured it was best to check with an ISP internal host) all show this latency increase, but the latency doesn't jump around, which is another reason I don't believe its congestion related. It is always 29ms when working fine, and always 60ms when it's playing up.

Given the next hop is beyond the dslam and who knows where (Sydney I'm guessing, my experience with production DSL networks is purely a customer level view) I have no visibility as to what is occurring there, but from all the things I can see, it's not my network causing it. A modem restart doesn't seem to resolve it, though it's hard to tell seeing as my modem takes a few minutes to boot, it's often "resolved" before my modem comes back. I'm pretty sure a few times it was still broken briefly after my modem came back as well and it does resolve itself without my rebooting my modem too.

On the topic, my modem is a Cisco 887 running an IOS 15 version that was mostly / completely up to date when I last checked, though that was a little while ago. I have checked processor usage, memory, attenuation / noise, audible line quality (via the POTS phone) as well as the basic IP troubleshooting and log checks, nothing is coming up at all that would indicate a problem on my end.

The Questions:
1. Any ideas what might be causing this issue that could still on my end? I have checked all the obvious things, IP wise its rock solid, so it'd have to be on the DSL side, though nothing has changed on my gear for a long long time now.
2. Any ideas what might cause behaviour like this on the provider side? Anything I could suggest they look at in particular?
3. Any additional commands / checks I can do on my equipment to confirm / assist in diagnosing anything from items 1 or 2?

I had not had this problem in the past, my copper line seems to be in very good condition as I very rarely experience any dropouts or disconnections at all, this has just started recently and as of last night seems to possibly be getting worse...

Any advice / general theories are welcome :)

Thanks,
Ayden Beeson  B.InfoTech,  CCNA
Technology Specialist (Networks)
Division Of Information Technology
Charles Sturt University
P.O. Box 789
Albury NSW 2640
Ph :02 60519788
Fax:02 60519919
abeeson at csu.edu.au<mailto:abeeson at csu.edu.au>
www.csu.edu.au<http://www.csu.edu.au>

Charles Sturt University

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