Strange public traceroutes return private RFC1918 addresses

From: "Terry Baranski" <>
Date: Tue, 3 Feb 2004 16:42:55 -0600

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

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

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