Re: Queue drops with FTP

Hi.
Your buffers are set to 307ms in CM-FIN class
(1500 packets x 256 Bytes x 8 / 10 000 000 = 0.307 seconds)

1. Yes, drops are slowing down the application
2. There is no way to avoid drops, except for special application-level
shaping/programming

FTP is trying to send as fast as you PC's connection, where FTP is running.
If you want no drops, you can go to the PCs adapter settings, and change
the speed to 10/FULL (and do so on the device where PC is connected to).
Then the FTP is not going to send faster.

Generally, TCP/IP is built that it wants to send at the maximum speed
possible, so if you'd have 10G card in your PC, it would send at 10G, and
drops would occur on the router.

If you want better performance, there are too many things that you can do
to describe here. You can target TCP option negotiation and optimization,
reduce delay by reducing buffer sizes, increase drop resiliency by enabling
selective acks, decrease timers, improve TCP window recovery, offload
shaper to a hardware device (e.g. switch), etc. etc.

On Wed, Oct 26, 2011 at 5:24 PM, BALAKRISHNAN Balaji <
Balaji.BALAKRISHNAN_at_swift.com> wrote:

> All,
>
> I need help to understand and resolve the queue drop issue with FTP..
> The
> traffic is shaped to 10Mbps but noticing huge queue drops when using
> FTP...Suspecting that the FTP pushing more traffic within the traffic
> shaping
> interval (25ms) though the 30sec offered rate indicates less than 10Mbps.
> How
> do I resolve this the problem without increasing the shape average.. Can I
> increase sustained bits/interval thereby increasing the shaping sampling
> interval ?? Does that affect the application performance ??
>
> policy-map PM-parent_generic-PW_temp
> class CM-FIN
> shape average 10000000
> queue-limit 1500
> class class-default
> shape average 2000000
>
>
> USPR1#sh policy-map interface GigabitEthernet0/3.1301
> GigabitEthernet0/3.1301
>
> Service-policy output: PM-parent_generic-PW_temp
>
> Class-map: CM-FIN (match-all)
> 41263 packets, 57551708 bytes
> 30 second offered rate 6552000 bps, drop rate 639000 bps
> Match: ip dscp af11 (10)
> Traffic Shaping
> Target/Average Byte Sustain Excess Interval Increment
> Rate Limit bits/int bits/int (ms) (bytes)
> 10000000/10000000 62500 250000 250000 25 31250
>
> Adapt Queue Packets Bytes Packets Bytes Shaping
> Active Depth Delayed Delayed Active
> - 0 37738 52215350 18690 27074295 no
>
>
> Rgds
> Bala.
>
>
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-- 
Pavel Bykov
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