[c-nsp] FW: L2 network - MPLS question

Saku Ytti saku at ytti.fi
Fri May 6 13:59:28 EDT 2016


On 6 May 2016 at 19:17, Rick Martin <rick.martin at arkansas.gov> wrote:

Hey,

> We are deploying Catalyst 3650;s with ASA's at the customer sites, using Nexus 9504's for our aggregation sites. All hardware was spec'd by Cisco, this was a very big deal and they brought in MANY Cisco internal resources to come up with the design and BOM.

3650 has 12MB shared buffer, TCP window grows exponentially and ~all
implementations burst (rather than pace) growth in linerate. If only
single port is being used, 12MB is good enough for about 200ms RTT for
1GB. 1Gbps * 200ms = 25MB, but worst-case you'd grow the window
12.5MB, and if sender is faster, like 10Gbps, then you'd essentially
see this whole burst in your buffers.
So from HW POV, 3650 isn't going to be significant limitation to your
single TCP session speed, unless you want to get 1GB from China or
something like that.

>  Customer experience is still poor, we have learned that using iperf or other download based speed testing tools we see a maximum of about 150Mbps download or upload speed.  If we configure the tools to use multiple threads we can see the WAN connection support full 1Gbps throughput.

64kB / 150Mbps = 3.4ms. Is the latency about 3.4ms? If so, then you'll
need window scaling turned on.
-- 
  ++ytti


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