high latency ds3 issue on unloaded line

kris foster kris.foster at gmail.com
Fri Sep 26 14:17:14 CDT 2008


Even if this is happening, the distance you can travel at 2/3 sol says  
there is something else going wrong here (1 sec latency is a very long  


On Sep 26, 2008, at 11:59 AM, John Lee wrote:

> Mike,
> Your latencies which suddenly appear for several hours and then go  
> away and do this on a regular basis  sounds like a layer 2, facility  
> switching issue. As you indicated " the problem comes on during the  
> day and then lets up late in the evening" sounds like the under  
> lying facility is being switched back around the "long side" of the  
> SONET ring or other facility. Some carrier facilities are scheduled  
> for "one path or direction" say during the day that are supposed to  
> be for lower latency time periods for interactive work and then  
> switch for a lower cost, higher latency path in the evening when  
> computer to computer backups do not care. If you can plot the times  
> the issues start and end and that these occur daily during the week  
> and not on weekends etc that would be a strong indicator.
> John (ISDN) Lee
> ________________________________________
> From: mike [mike-nanog at tiedyenetworks.com]
> Sent: Friday, September 26, 2008 12:04 PM
> To: nanog at nanog.org
> Subject: high latency ds3 issue on unloaded line
> Hello,
>    I have a ds3 from qwest which has daily issues with insane
> point-to-point latencies sometimes exceeding 1000ms for hours on end,
> and which suddenly disappear, and does not appear to correspond with
> actual measured link utilization (less than 20mbps most days).
>    To make a long investigation short, the problem comes on during the
> day and then lets up late in the evening. I have tested and examined
> everything at the ip layer and no it's not high utilization, an ACL,
> router cpu or bad hardware, no line errors or other issues visible  
> from
> interface or controller stats. yes I have flushed all hardware, and I
> have a 7204vxr/npe-400 with this single ds3. The only clue seems to be
> millions of 'output drops' from qwest's side. And at night I can hit
> popular ftp mirrors from a directly attached server and observe my
> interface reporting about %100 utilization combined with my users and
> customers, so yeah it really is a full line rate ds3. And historically
> Mrtg always shows around 20mbps or less utilization and it's only
> smokeping that goes off, usually in the afternoon when the point to
> point latencies between my router and qwest start heading north, and
> consistently at that. I also have another in house tool that takes 30
> second snapshots of my ds3 interface in order to catch short bursts  
> that
> would be smoothed out with mrtg's 5 minute average, but during these
> high latency times there aren't any spikes noted. And for added
> confusion (or fun!), the latency can start at any utilization level -
> I've observed it while we were pulling just 12mbps, and I have not had
> it while we were doing 34mbps, only the time of day seems to be the
> common factor.
>    Qwest has not been able to identify the issue, only note that -
> yeah, this really is happening when there is otherwise no real load on
> the line - and I am certain we have done everything to rule out the ip
> layer. They have put in a 'request' to move me to another router,  
> but I
> am not hopeful of a resolution that way as the router we're  
> currently on
> doesn't appear otherwise to have the problem with any other  
> subscriber.
>    What I want to know, is it possible that the underlaying atm/sonet
> that carries my ds3 from my facility is somehow oversubscribed or
> misconfigured? We have an OC12 fiber entrance and this is the only
> circuit provisioned on it, and in our small tiny town the only other
> user on the ring with us is comcast (according to the att network
> engineer who installed this). I don't know enough about atm/sonet to
> imagine conditions that would cause the issues I am seeing here , but
> every ip layer tool I have only ever tells me there isn't an ip issue
> here. I can issue ping from my router directly to the attached qwest
> router and get > 1000ms and then other times (out of the problem
> window), I am getting 4ms.
>    If anyone has laughs or beers to offer me, send 'em on cuz I could
> use both right about now....
> Mike-

More information about the NANOG mailing list