[c-nsp] C6800 Sup2T buffering ?

[James Bensley]

On Wed, 20 May 2020 at 21:45, james list <jameslist72 at gmail.com> wrote:
>
> Dear experts
> my customer have some multicast flows which are detected sometime with
> peaks/latency.
>
> They measure this latency based on protocol financial feed timestamp which
> I'm not able to decode (I guess they use stuff like Corvil).
>
> The path from the market datafeed source to the customer is:
>
> Financial market --1Gb -- C6807 VSS SUP2T  -- 10 G port-channel WAN --
> C6807 VSS SUP2T -- 1 Gbs -- Arista 7150S --1 Gbs -- customer
>
> They report 10-15 ms average latency and sometimes they detect 500-600 ms.
>
> Following the path I do not find anything telling me there are spikes (I
> have no drops) and also the customer states no packet loss is detected, but
> we suspect buffering/queuing somewhere on C6807 or Arista 7150S.
> Since Arista 7150S is low latency I suspect Cisco.
>
> Some questions:
> - what do you suggest to check here ? buffers ? qos ? other...
> - what I can use to try to decode pcap taken on Arista switch to check if
> the latency is really obtained checking protocol market timestamp ?

Hi James,

Perhaps a good start would be to narrow down where the increase in
latency is coming from.

I'd start by finding a way to packet capture as they come into the
first C6807 VSS SUP2T over the 1G link from the financial market, to
check that the problem is even within your control domain, and then
work backwards along the path from there, making the packet capture
along each link until I find the culprit of the latency spikes.

Cheers,
James.