Subject: [pmtud] Links with tiny MTUs

From: "Templin, Fred L" <[email-masked]>
Date: Fri, 12 Aug 2005 09:48:04 -0700

In Matt Zekauskas' meeting minutes from IETF62, there was some
discussion about PMTUD implications for links with tiny and
unusual-sized MTUs, e.g., IEEE 802.15.4 low power personal area
networks configure MTUs as small as 81 bytes. But, "Transmission
of IPv6 Packets over IEEE 802.15.4 Networks" (draft-ietf-6lowpan
-format-00.txt) specifies a fragmentation/reassembly scheme that
supports the IPv6 minimum MTU of 1280 bytes through what is
essentially a link-layer adaptation scheme below IP.

This would seem to ease the fine-scan burden for PMTUD, since
it would see an MTU of 1280 bytes across 6lowpan links. It also
sets a precendent for other links with tiny and unusual-sized
MTUs that (if followed) would make life easier for PMTUD.

It seems to be generally accepted that these kinds of links will
occur only at the edges of the network, and not somewhere in
the middle. But, has anyone conducted a survey of links with
tiny MTUs to enumerate the types of links, whether/not they
are widely-deployed and whether/not they support link adaptation
for packet sizes up to the IPv6 minimum MTU of 1280 bytes?

Fred
[email-masked]      

_______________________________________________
pmtud mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/pmtud