Re: Strange public traceroutes return private RFC1918 addresses

["Kevin Oberman" <oberman () es net>]

> From: "Terry Baranski" <tbaranski () mail com>
> Date: Tue, 3 Feb 2004 16:42:55 -0600
> Sender: owner-nanog () merit edu
>
>
> Leo Bicknell wrote:
>
> > Since most POS is 4470, adding a jumbo frame GigE edge makes
> > this application work much more efficiently, even if it doesn't 
> > enable jumbo (9k) frames end to end.  The interesting thing 
> > here is it means there absolutely is a PMTU issue, a 9K edge
> > with a 4470 core.
>
> This brings up the question of what other MTUs are common on the
> Internet, as well as which ones are simply defaults (i.e., could easily
> be increased) and which ones are the result of device/protocol
> limitations.  
>
> And why 4470 for POS?  Did everyone borrow a vendor's FDDI-like default
> or is there a technical reason?  PPP seems able to use 64k packets (as
> can the frame-based version of GFP, incidentally, POS's likely
> replacement).  

4470 was, as you surmised, to allow a full sized FDDI packet to be
packed into a single POS packet. At the time FDDI was using larger
packets than anything else.

Now the recommendation for research and education networks (Abilene,
ESnet, NASA, and many Asian and European R&Es) is 9000 and, within that
community, is almost universally adopted when the hardware will support
it.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman () es net                       Phone: +1 510 486-8634