[Bloat] Jumbo frames and LAN buffers

[Jim Gettys]

On 05/16/2011 09:42 AM, Kevin Gross wrote:
> I would like to try this. Can you suggest specific equipment to look at. Due
> to integration and low port count, most of the cheap consumer stuff has
> surprisingly good layer-2 performance. I've tested a bunch of Linksys and
> other small/medium business 5 to 24 port gigabit switches. Since I measure
> latency, I expect I would have noticed if flow control were kicking in.

I think I was using a D-Link DGS2208. (8 port consumer switch).

I then went and looked at the spec sheets of some of the other consumer 
kit out there and found they all had the "feature" of 802.3 flow control.

I may have been using iperf to tickle it, rather than ssh.

I was also playing around with an old 100Mbps switch, as documented in 
my blog; I don't remember if I saw it there.
                         - Jim

> Kevin Gross
>
> -----Original Message-----
> From: bloat-bounces at lists.bufferbloat.net
> [mailto:bloat-bounces at lists.bufferbloat.net] On Behalf Of Jim Gettys
> Sent: Monday, May 16, 2011 7:23 AM
> To: bloat at lists.bufferbloat.net
> Subject: Re: [Bloat] Jumbo frames and LAN buffers
>
> On 05/16/2011 09:15 AM, Kevin Gross wrote:
>> All the stand-alone switches I've looked at recently either do not support
>> 802.3x or support it in the (desireable) manner described in the last
>> paragraph of the linked blog post. I don't believe Ethernet flow control
> is
>> a factor in current LANs. I'd be interested to know the specifics if
> anyone
>> sees it differently.
> Heh.  Plug wireshark into current off the shelf cheap consumer switches
> intended for the home.  You won't like what you see.  And you have no
> way to manage them.  I was quite surprised last fall when doing my home
> experiments to see 802.3 frames; I had been blissfully unaware of its
> existence, and had to go read up on it as a result.
>
> I don't think any of the enterprise switches are so brain damaged.  So i
> suspect it's mostly lurking to cause trouble in home and small office
> environments, exactly where no-one will know what's going on.
>                           - Jim
>
>
>
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