[ale] PPP Perfromance

[Jeff Hubbs]

Boo.

I've gathered that these parameters (MTU, etc.) are controllable via
ifconfig but where are they typically stored?

- Jeff

On Fri, 2003-10-31 at 16:24, Dow Hurst wrote:
> The local LAN hardware that supports your LAN has to be able to handle 
> jumbo frames if you want to have larger packet sizes than 1500 bytes.  
> That is why Linux clusters using Gigabit switches have had to pay more 
> for the switches that would support jumbo frames if they want to 
> maximize the efficiency of the bandwidth.  The 1500 byte max is also a 
> limiting factor on PPPoE since the LAN behind the DSL router should have 
> an MTU of less than 1500.  How much less is debatable but the Roaring 
> Penguin software recommended 1412 if I remember correctly.  You want the 
> LAN ethernet frames to be efficiently packaged inside the PPP frame 
> which is packaged inside the ATM frame.  No wonder everyone wants a 
> straight ethernet instead of PPPoE for their broadband!!  Fragmenting 
> the local LAN packets just lowers the efficiency of your PPPoE 
> connection and the overhead of the router's rebuilding the fragmented 
> packets.
> 
> To switch to another topic of LAN efficiency at a different layer:  For 
> TCP and UDP packet size over a local LAN I've played with NFS packet 
> sizes to see what is most efficient. Here in our VPN at KSU I found that 
> udp and tcp required different values.  So, packet size at the ethernet 
> layer and at the higher layer has a big effect on efficiency.  Within a 
> local LAN on normal hardware 1500 MTU is best since you get the largest 
> ethernet packet per packet transmission while a UDP/NFS packet size of 
> 64K instead of the default 8K might increase efficiency.  It is good to 
> spend an afternoon testing such things to tune the network traffic.  I 
> use SGI IRIX so my NFS packet sizes for UDP and TCP might be tuned 
> differently than a Solaris or Linux based LAN.  I would imagine that as 
> Gigabit switches drop in price and that the models with jumbo packet 
> capability also drop that eventually we might be able to take advantage 
> on home LANs for passing video and such.  I don't know alot about jumbo 
> packets so I can't say anything other than just this little bit.  Jeff 
> Layton might have a comment?
> Dow
> 
> 
> Doug McNash wrote:
> 
> >
> > The max number of data bytes one can put in a 802.3 Ethernet frame is 
> > 1500 per IEEE standard
> >
> >
> > On Fri, 31 Oct 2003 10:53:49 -0500
> >  Geoffrey <esoteric at 3times25.net> wrote:
> >
> >> Doug McNash wrote:
> >> Getting back to the mtu issue, I'm now curious as to whether that 
> >> might be part of the problem why I couldn't get to my mother-in-laws 
> >> benefit web site.  I've played with mtu a bit and found a couple 
> >> things out. Currently all my ethernet networks are set at mtu 1500.  
> >> I can easily reduce this by simply:
> >>
> >> ifconfig eth0 mtu 1000
> >>
> >> But if I attempt to increase it, I get an error.  Me thinks this 
> >> would because there's a max set somewhere, although after running 
> >> around in /proc for a while, I couldn't find anything.  Anyone else 
> >> have any ideas?
> >>
> >>
> >> -- 
> >> Until later, Geoffrey    esoteric at 3times25.net
> >>
> >> Building secure systems inspite of Microsoft
> >>
> >> _______________________________________________
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> >> Ale at ale.org
> >> http://www.ale.org/mailman/listinfo/ale
> >
> >
> > -- 
> > Doug McNash <dmcnash at yahoo.com>
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> >
-- 
Jeff Hubbs <hbbs at comcast.net>