IPv6 MTUs smaller than 1280 bytes?

Fernando Gont fernando at gont.com.ar
Mon Sep 13 16:39:40 CEST 2010

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.


Kind regards,
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

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