[c-nsp] Weird throughput issue

Curtis Piehler cpiehler2 at gmail.com
Sun Jul 24 18:13:32 EDT 2016

Oh right.   I temporarily move the wan to an svi on the cat4900

On Jul 24, 2016 6:09 PM, "Andrew Miehs" <andrew at 2sheds.de> wrote:

> On Sun, Jul 24, 2016 at 7:11 PM, Curtis Piehler <cpiehler2 at gmail.com>
> wrote:
> > Hi Andrew,
> >
> > Thank you for the reply.  The cat4900 and 6504 are acting as a pure
> Layer 2
> > trunking device.   The carrier NNI comes into the Cat4900 and the
> customer
> Understood, which, but you mentioned 3-4ms between 2911 and c4900.
> How did you measure this time if the c4900 is trunking?
> ...
> > out.  Based on this I know I should at least see 20-25M to this site
> from my
> > IPERF servers.  Latency to one of my IPERF servers is 17ms and the other
> is
> > 35ms.  The IPERF server that sees 17ms can not push anymore than 5-6M
> > through the router.  The IPERF server that sees 35ms can not push
> anything
> > more than 2M to the router.
> ....
> > to TTCP test to this site I can push nearly 20-25M based on the
> calculation
> > above with no issues (The processor maxes out near 25M).  When I repeat
> the
> > same test to the site with the problem (using the same Transmit/Receive
> > Window) the results are consistent with the paragraph above,.
> What are your receive window sizes? (And I don't mean MSS or MTU)
> The descriptions above are a little unclear, and it may help you to
> create some form of table to see what happens with which combinations.
> > The only difference in the setup between both sites is 1) the carrier(s)
> > that is used and 2) the site with the problem trunks through a Cat4948
> > initially before hitting the 6504.  We have other customers off of the
> > Cat4948 who report no issues.  I have looked over the Cat4948 config and
> > there is nothing apparent that would hinder TCP taffic.
> So based on this description, you believe you only have one
> difference, which is the link from the carrier itself.
> I would recommend confirming with them whether they have incorrectly
> provisioned your link, and set policers/ qos settings incorrectly. I
> would also confirm with them that they haven't oversubscribed part of
> their backbone.
> Have you run tcpdump on your iperf instance to see what is happening?
> This will show you pretty quickly whether you are experiencing
> retransmits, or if one side has not enabled window scaling.
> > This whole problem started when the customer went to do a speed test from
> > the problem site and couldn't even break 5M on the download and 50-60M
> > upload.  When the customer speed tests from the other site that comes
> into
> > the Cat6504 that trunks up to the same ASR9K they can obtain 90/90.
> And I assume you have checked the interfaces and CPU on the c2911? No
> drops, pause frames?
> Once again, ask the carrier whether they have any issues on their link.
> Should you have no luck with the tcpdumps, it may be quickest to
> connect PCs directly to either end of this link (it is copper?) and
> then test point to point to take all other hardware out of the
> equation.
> >
> > I've also applied 90M shapers on both ends of the WAN to avoid hitting
> the
> > carrier policers in the middle and it had no effect.
> This is a good idea, but just be aware that this may increase jitter
> which may be an issue if the link is being used for voip.
> Is it correct to assume that you configured the shapers on the asr9k
> and the c2911?

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