[c-nsp] Performance issue on link

Arie Vayner (avayner) avayner at cisco.com
Mon Apr 1 19:20:34 EDT 2013

You need to shape your traffic to 40Mbps (or most likely slightly less than that).
TCP bursts and your provider drops the traffic, which causes the TCP window to shrink.

Your switches cannot shape, so you would have to do it on the routers.

Basically, a classic sub-rate link problem:


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of CiscoNSP List
Sent: Monday, April 01, 2013 15:51
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Performance issue on link


We have a 40Mb link between 2 POPs - Latency ~65m/sec (No packet-loss)

POP A Is a 7301 and 2960POP B is a 7200 and 4948

40Mb link is connected to the two switches (L2), and then a trunk link to both routers for all L3.

Have a Linux server connected to both switches, and achieve the following performance:

POP A -> POP B - 38.5Mb/secPOP B -> POP A - 38.5Mb/sec

POP A -> POP B - ~20Mb/secPOP B -> POP A - ~12Mb/sec

POP A -> POP B - ~38Mb/secPOP B -> POP A - ~16Mb/sec

POP A -> POP B - ~30Mb/sec POP B -> POP A - ~16Mb/sec

Any suggestions on why I am seeing poor performance with TCP transfers? (Especially POP B -> POP A direction) - I've tried adjusting the window size in IPERF but it actually made the results worse?
Thanks in advance.

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