[183366] in North American Network Operators' Group
Re: PMTUD for IPv4 Multicast - How?
daemon@ATHENA.MIT.EDU (William Herrin)
Mon Aug 31 17:38:43 2015
X-Original-To: nanog@nanog.org
X-Really-To: <nanog@nanog.org>
In-Reply-To: <55E4C450.7070004@necom830.hpcl.titech.ac.jp>
From: William Herrin <bill@herrin.us>
Date: Mon, 31 Aug 2015 17:38:14 -0400
To: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
On Mon, Aug 31, 2015 at 5:17 PM, Masataka Ohta
<mohta@necom830.hpcl.titech.ac.jp> wrote:
> for routers, generating ICMP PTB is as burdensome
> as generating fragments?
No, it isn't.
When a router fragments a packet, it has to fragment the next and the
next and the next. Maybe tens or hundreds of thousands of packets
before the end of that one user's session.
When a router generates a PTB, there is no next. PTB is a soft
failure. The origin must correct the error (by reducing packet size)
before communication can succeed.
There are potentially several orders of magnitude of difference in the
burden on the router.
Regards,
Bill Herrin
--
William Herrin ................ herrin@dirtside.com bill@herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>
