[183362] in North American Network Operators' Group
Re: PMTUD for IPv4 Multicast - How?
daemon@ATHENA.MIT.EDU (William Herrin)
Mon Aug 31 16:39:06 2015
X-Original-To: nanog@nanog.org
X-Really-To: <nanog@nanog.org>
In-Reply-To: <20150831.214943.74737034.sthaug@nethelp.no>
From: William Herrin <bill@herrin.us>
Date: Mon, 31 Aug 2015 16:38:36 -0400
To: sthaug@nethelp.no
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
On Mon, Aug 31, 2015 at 3:49 PM, <sthaug@nethelp.no> wrote:
> ICMP replies to multicast packets can cause ICMP "implosion". This is
> not a new discussion - see for instance
>
> http://mailman.nanog.org/pipermail/nanog/2012-June/048685.html
It's a shame we handle path MTU as a layer 3 problem that gets an ICMP
response from a middlebox. It'd make more sense to truncate the
packet, set a flag, and then let layer 4 at the recipient deal with
negotiating a new size with the sender. You know, end to end principle
and all. That'd eliminate the problems with firewall-blocked protocols
and routers using private IP addresses, the usual culprits for pmtud
breakage.
It'd also let multicast protocols make reasonable choices for that
particular protocol without being stuck with the stack's default.
-Bill
--
William Herrin ................ herrin@dirtside.com bill@herrin.us
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/>
