IPv6 MTUs smaller than 1280 bytes?

[Brian E Carpenter]

Gert

On 2010-09-12 23:56, Gert Doering wrote:
> Hi,
> 
> On Sun, Sep 12, 2010 at 05:51:22AM +0000, bmanning at vacation.karoshi.com wrote:
>> On Sat, Sep 11, 2010 at 09:09:52PM +0200, Gert Doering wrote:
>>> On Sat, Sep 11, 2010 at 12:49:19AM +0000, bmanning at vacation.karoshi.com wrote:
>>>> 	i will admit to truting what my tools tell me, and 
>>>> 	they report an MTU of 1220.  It appears to be from a
>>>> 	single vendors kit.
>>> Is that due to a broken implementation, or due to actual link-layer
>>> technology that cannot handle more than 1220?
>> 	are these two different?
> 
> Yes.  Broken implementations can be fixed or replaced by a different
> vendor's working implementation.
> 
> Technology that cannot do larger MTUs because of the way the technology
> is specified (imagine ATM without SAR at the VC endpoints) cannot be 
> fixed without changing standards, upgrading lots of different vendor
> implementations, etc.

What's supposed to happen then is that the logical link layer handles
fragmentation as a link layer (or maybe layer 2.5) function, so that
the IPv6 layer still sees at least 1280.

> Just to spell out why I think there is a difference :-) - in the specific
> moment in time "I want to transfer a packet now and it does not go through",
> there is no effective difference, of course.

Indeed not.

   Brian

> 
> Gert Doering
>         -- NetMaster