North American Network Operators Group

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Re: MTU of the Internet?

  • From: Eric Osborne
  • Date: Thu Feb 05 09:46:30 1998

> On Thu, 5 Feb 1998, Perry E. Metzger wrote:
> > Eric Osborne writes:
> > > The problem with anything Microsoft may put forth is that it'll read
> > > like "576 is good.  It is the best.  We do it.  So should everybody.
> > > If 576 is good, all else must be bad."  And that's simply not the
> > > case.
> > 
> > I must admit that I'm very worried about what will happen to the
> > internet if they do this. Why?
> > 
> > This will effectively triple the number of packets that routers have
> > to do processing on, that's why.
> Packets going through our border routers have an average packet size
> in the region of 200 to 250 bytes.  How would this triple the average
> packet size?

I think that "triple" is perhaps an oversimplification.  This assumes that
without a 576-byte MTU, all packets would be 1500-byte MTUs.  1500/576 ~=~ 3.

Remember, there's three kinds of average: mean, median, mode.  While the mean 
packet size may be 200-250 bytes, the mode and median are probably different.  
I don't have any statistics on this, but I'd be willing to guess that if you 
plotted the packet sizes frequency you'd see something like a bimodal curve, 
with a small peak at around 64 (ping) and a larger one near 1500 (10Mbit 
Ethernet/T1 MTU).  As to median packet size, I have no idea.  It's probably 
somewhere in the middle.  :)