jumbo frames

Thu Apr 26 20:50:59 UTC 2001

You are correct and my original answer stated such. The original question
didn't differentiate. It simply asked who was using jumbo packets.

> -----Original Message-----
> From: Tony Hain [mailto:alh-ietf at tndh.net]
> Sent: Thursday, April 26, 2001 12:55 PM
> To: Roeland Meyer; ALH-IETF; John Fraizer; Paul Lantinga
> Cc: nanog at merit.edu
> Subject: RE: jumbo frames
> 
> 
> 
> Roeland you are talking about jumbo frames from the end 
> system lan, while
> John is talking about only using the jumbo frames between the 
> routers. My
> point was that in John's environment the packets will all be 
> 1500 since the
> packets are restricted to that size just to get to the router 
> with the GE
> interface. I understand that there are perf gains as long as 
> the entire path
> supports the larger packets, but I don't understand the claim 
> that having a
> bigger pipe in the middle helps.
> 
> Tony
> 
> -----Original Message-----
> From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu]On Behalf Of
> Roeland Meyer
> Sent: Thursday, April 26, 2001 12:13 PM
> To: 'alh-ietf at tndh.net'; John Fraizer; Paul Lantinga
> Cc: nanog at merit.edu
> Subject: RE: jumbo frames
> 
> 
> > From: Tony Hain [mailto:alh-ietf at tndh.net]
> > Sent: Thursday, April 26, 2001 11:47 AM
> >
> > April 26, 2001 9:29 AM John Fraizer wrote:
> > > We only have jumbo frames enabled on router<->router links.
> >  The GigE
> > > ports facing the aggregation switches runs standard 1500 MTU.
> >
> > Hence my original question. Packets across the GE will be
> > 1500 unless you
> > are packing them.
> >
> > April 25, 2001 8:10 PM John Fraizer wrote:
> > > Partially because I can.  Partially because there seems to be a
> > > performance increase when you start stuffing the pipe.
> >
> > Assuming you are just passing the packets as received from
> > the aggregation
> > switch, this would only happen if your router hardware was better at
> > managing jumbo buffer allocations than 1500B ones. Clearly it
> > will waste
> > large chunks of memory, so do you have measurements to show 
> the actual
> > performance increase?
> 
> This depends on the type of traffic. We use it to enhance 
> performance of the
> data tier. We've jiggered the TCP/IP stacks for ~4500 byte 
> packets and have
> knee-capped the slow-start algorithm (which doesn't make 
> sense in a pure
> switched environment anyway). What we then wind up with, is a 
> dedicated data
> LAN between our application servers and the Oracle database 
> servers. It
> comes out to about an order of magnitude increase in 
> performance and SQL
> query responsiveness. At first we went to jumbo packets. We saw such a
> radical improvement that we started investigating and found 
> the slow-start
> issue. Jumbo packets are one way around the slow-start 
> problem if you can't
> jigger the stack itself. Most of the queries are reasonably 
> short so we saw
> some serious improvements by killing the slow-start. If you 
> can modify your
> IP stack then it still pays to use jumbo packets because you 
> reduce the
> overhead on the wire.
> 
> We got sufficient performance improvement that we were able 
> to defer GigE
> implementation, at some sites. Those sites are using switched 
> FDX 100baseTX.
> 
> 