Common operational misconceptions

Mark Andrews marka at
Thu Feb 16 04:27:39 UTC 2012

In message <4F3C76D5.9040603 at>, Masataka Ohta writes:
> Mark Andrews wrote:
> > This doesn't prove that IPv6 is not operational.  All it proves is
> > people can misconfigure things.
> How do operators configure their equipments to treat
> ICMP packet too big generated against multicast and
> unicast?

Well you need to go out of your way to get a ICMP PTB for IPv6
multicast as the default is to fragment multicast packets at the
source at network minimum mtu (RFC3542 - May 2003).  That's not to
say it won't happen.

As for generation of PTB you rate limit them the way you do for

> Note that, even if they do not enable inter-subnet
> multicast in their domains, the ICMP packets may
> still transit over or implode within their domains.
> Note also that some network processors can't efficiently
> distinguish ICMP packets generated against multicast and
> unicast.

And why do you need to distingish them?  You look at the inner
packet not the ICMP source if you want to rate limit return traffic.

> 					Masataka Ohta
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at

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