Subject: Minimum IPv6 MTU

From: Fernando Gont <[email-masked]>
Date: Thu, 10 Jul 2008 17:30:22 -0300

Folks,

RFC 2460 states that every link in an internet have an MTU of 1280 
octets or greater, and that any link that cannot convey a 1280-octet 
packet in one piece must provide fragmentation and reassembly at a 
layer bellow IPv6.

However, while talking about the specs with a few folks (who 
preferred to remain anonymous), it was mentioned to me that in a 
number of scenarios (not necessarily those that involve tunnels), 
some links have an MTU smaller than 1280, and they do not perform the 
"fragmentation and reassembly function at a layer bellow IP" that RFC 
2460 requires.

Any operational data or experiences with those link technologies will 
be more than welcome.... either on- or off-list.

Thanks!

Kind regards,

--
Fernando Gont
e-mail: [email-masked] || [email-masked]
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1

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From: Jeroen Massar <[email-masked]>
Date: Thu, 10 Jul 2008 23:34:44 +0200

Fernando Gont wrote:
> packet in one piece must provide fragmentation and reassembly at a layer 
> bellow IPv6.
> 
> However, while talking about the specs with a few folks (who preferred 
> to remain anonymous), it was mentioned to me that in a number of 
> scenarios (not necessarily those that involve tunnels), some links have 
> an MTU smaller than 1280, and they do not perform the "fragmentation and 
> reassembly function at a layer bellow IP" that RFC 2460 requires.

Then those links have to be fixed. Simple, nothing to it ;)

This is why there are a couple of RFC's that explicitly detail how these 
links are used to transmit/use IPv6. Some for instance don't support 
multicast which thus breaks the whole concept of Neighbor Discovery etc.

Thus if you know any linktype which is not able yet to properly do IPv6, 
document them as a draft and submit it.

Greets,
  Jeroen