In message <[email protected]>, james woodyatt 
writes:
> On Jun 25, 2013, at 20:30 , Fred Baker (fred) <[email protected]> wrote:
> > On Jun 25, 2013, at 12:42 PM, Randy Bush <[email protected]> wrote:
> >> 
> >> in reality, you can not count on pmtud working
> 
> In reality, you can not count on the Internet working.  Despite that, it 
> mostly works, most everywhere you need it to wor
> k, most of the time.  Only occasionally, does one encounter failure.
> 
> > One of these days, I'll understand why Linux/FreeBSD/Windows/Apple don't 
> > implement RFC 4821. 
> 
> One of these days, I'll understand why operators don't make it MANDATORY for 
> all hosts on their networks to implement RFC
>  4821 before they configure their routers to break ICMPv6 path MTU discovery.

I don't know why firewall vendors permit configurations that block
icmpv6 PTB while passing ipv6 packets bigger than 1280 over the same
interface.  Such a configuration is broken.

If you don't want to let icmpv6 PTB in then set the MTU to 1280 and
generate icmpv6 PTB for anything bigger than 1280 yourself.

> --
> james woodyatt <[email protected]>
> core os networking
> 
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