[67178] in North American Network Operators' Group
Re: Strange public traceroutes return private RFC1918 addresses
daemon@ATHENA.MIT.EDU (Kevin Oberman)
Tue Feb 3 18:47:13 2004
To: "Terry Baranski" <tbaranski@mail.com>
Cc: nanog@merit.edu
In-Reply-To: Message from "Terry Baranski" <tbaranski@mail.com>
of "Tue, 03 Feb 2004 16:42:55 CST." <005101c3eaa7$11271d80$0200000a@pleth0ra>
Date: Tue, 03 Feb 2004 15:37:43 -0800
From: "Kevin Oberman" <oberman@es.net>
Errors-To: owner-nanog-outgoing@merit.edu
> 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
