IPv6 MTUs smaller than 1280 bytes?

[Ralph Droms]

As far as I know, the 6lowpan adaptation layer is the first definition of IPv6-over-802.15.4

- Ralph

On Sep 13, 2010, at 11:23 PM 9/13/10, Fernando Gont wrote:

> Hi, Ralph,
> 
> Does 802.15.4 predate 6lowpan? Put another way: maybe there are
> deployments of IPv6 (no 6lowpan) over 802.15.4?
> 
> Thanks!
> 
> Kind regards,
> Fernando
> 
> 
> 
> 
> Ralph Droms wrote:
>> Just to be clear - the 6lowpan adaptation layer for
>> IPv6-over-802.15.4 does define its own fragmentation, which should
>> appear to provide an MTU of 1280 to IPv6.
>> 
>> - Ralph
>> 
>> On Sep 13, 2010, at 5:58 PM 9/13/10, Fred Baker wrote:
>> 
>>> On Sep 13, 2010, at 7:39 AM, Fernando Gont wrote:
>>> 
>>>> Hi, Fred,
>>>> 
>>>>>> Thanks.  So how do people adapt IPv6 to 802.15.4-2006?
>>>>> They're using PMTU. On the local side you can know that it is 
>>>>> 802.15.4 and set a TCP MSS very small, but unless one side does
>>>>> that the other has no way to detect the problem apart from
>>>>> PMTU.
>>>> Just double checking: So... these link layers do not support MTUs
>>>> of 1280 bytes?
>>>> 
>>>> e.g., what if the flow does not implement PMTUD?
>>>> 
>>>> FWIW, I'm just trying to figure out if, when receiving an ICMP
>>>> PTB that advertises a Next-Hop MTU smaller than 1280, it is
>>>> really safe to *not* fragment the original packet in fragments of
>>>> (at most) the advertised MTU.
>>>> 
>>>> If there are link layers that do not support an MTU of 1280 bytes
>>>> then, despite of what RFC 2460 requires, one may need to be more
>>>> careful in this case, as sticking to 1280-byte packets may result
>>>> in interoperability problems.
>>> duh. :-)
>>> 
>>> If you get a message back telling you to fragment to 50 bytes, I'd
>>> suggest you do so.
>> 
>> 
> 
> -- 
> Fernando Gont
> e-mail: fernando at gont.com.ar || fgont at acm.org
> PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1
> 
> 
> 
>