Fixing MTU issues - would somebody like a 'tracepath6 from 47 different ISPs'?

Matsuzaki Yoshinobu maz at
Tue Jun 7 12:12:57 CEST 2011

Date: Tue, 7 Jun 2011 11:57:48 +0200
Andrew Yourtchenko <ayourtch at> wrote
> On Tue, Jun 7, 2011 at 11:46 AM, Jeroen Massar <jeroen at> wrote:
>> First an insult: Folks who think that blocking ICMP is 'smart' and
>> 'secure' please upgrade your brain and fix your local issue and at least
>> don't block ICMP Packet Too Big, it really is needed for a proper
>> functioning of the Internet.
> +1.
> Though sometimes it is a bit more complicated than just ICMP being blocked.
> (speaking from personal experience with tracking down s/w bugs).

Yes, it's complicated actually.  Folks who are using smaller MTU links
in their network should look into their router's configuration.  By
defalut, cisco ios originates only 1 icmp error every 100msec(0.1pps),
and juniper junos originates 1000 icmp (including echo replies)
packets/sec.  This leads the PMTUd failures in some cases.

see also:
Matsuzaki Yoshinobu <maz at>
 - IIJ/AS2497  INOC-DBA: 2497*629

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