[183368] in North American Network Operators' Group
Re: PMTUD for IPv4 Multicast - How?
daemon@ATHENA.MIT.EDU (Masataka Ohta)
Mon Aug 31 20:49:53 2015
X-Original-To: nanog@nanog.org
Date: Tue, 01 Sep 2015 09:49:47 +0900
From: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
To: William Herrin <bill@herrin.us>
In-Reply-To: <CAP-guGUPN2vDdFC1qwkD2FOBQKYjWWRd=07ywpkCz28h_GJ3Bw@mail.gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
William Herrin wrote:
>> for routers, generating ICMP PTB is as burdensome
>> as generating fragments?
>
> No, it isn't.
Yes, it is. Generating an ICMP PTB @aclet is as burdensome as
fragmenting a packet.
> 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.
Not necessarily, because transport layer can react against fragmented
packets.
> 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)
What if, the origin does not reduce packet size?
Masataka Ohta
