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When I start "iperf -s" on the one system and start "iperf -c -i 1 -t 3600 -d" on the other, I see an asymmetric bandwidth usage. The following trace show the trace taken on the client side system:

I am having two port switch, one is set to 1000M and another to 100M with full duplex, autoneg ON.

Laptop1 - sw1(port speed 1G) - sw2(port speed 100M) - laptop 2
>>>>>Asymmetric bandwidth.

[  5] local 10.110.23.157 port 43173 connected with 10.110.23.163 port 5001
[  4] local 10.110.23.157 port 5001 connected with 10.110.23.163 port 50234
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0- 1.0 sec  26.0 MBytes   93.3 Mbits/sec
[  4]  0.0- 1.0 sec  2.50 MBytes  21.0 Mbits/sec
[  5]  1.0- 2.0 sec  26.5 MBytes  93.4 Mbits/sec
[  4]  1.0- 2.0 sec   704 KBytes  5.77 Mbits/sec
[  5]  2.0- 3.0 sec  27.1 MBytes   91.0 Mbits/sec
[  4]  2.0- 3.0 sec   445 KBytes  3.65 Mbits/sec
[  5]  3.0- 4.0 sec  26.2 MBytes   93.3 Mbits/sec
[  4]  3.0- 4.0 sec   410 KBytes  3.36 Mbits/sec

There is a big discrepancy 93 MBit vs 3.5 MBit

on the other hand, If i set:

Laptop1 - sw1(port speed 1G) - sw2(port speed 1G) - laptop 2
>>>>>Symmetric bandwidth.
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  • 1
    Looks like your switch has a single packet cache per port. Laptop 1 dominates the cache since it has 10x the line rate. This leaves relatively little chance of Laptop 2 getting anything into the cache, and you get the wildly asymmetric throughputs.
    – Chris S
    May 6, 2013 at 12:57
  • @ChrisS Without knowing the brand/model of switch that would be my first guess as well.
    – Tonny
    May 6, 2013 at 14:05
  • I am having cpsw switch(3psw).
    – Tanmay N
    May 9, 2013 at 9:11
  • I am having cpsw switch(3psw). I am getting symmetric bandwidth if I set both ports at same speed. This issue is only if ports are at different speed.
    – Tanmay N
    May 9, 2013 at 9:42
  • The configurations on laptop are: Laptop 1: speed: 1000M duplex: full autoneg: on Laptop 2: speed: 100M duplex: full autoneg: on SW1 and SW2 are the cpsw external ethernet ports, which are linked through hardware link.
    – user174742
    May 22, 2013 at 5:56

1 Answer 1

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This could result from a duplex mistmatch between laptop 2 and sw2. Is laptop 2 showing 100/full and autoneg? Sw2 may be sending full duplex, but laptop 2 could be in half duplex so it's colliding with packets coming downstream to it.

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