Path MTU discovery and IPv6-in-IPv4 tunnels

["Fred L. Templin" <ftemplin@IPRG.nokia.com>]

(Re-posting this here from the IPng list:)

In the packetization layer path MTU discovery (plpmtud) bof at IETF 56,
we were shown a new method for determining path mtu that does not rely
on ICMPs. For more details, see the BOF agenda at:

  http://www.ietf.org/ietf/03mar/plpmtud.txt

The plpmtud method expects link layers to pass the largest possible
packets while being consistent about what packet sizes are acceptable,
but this can be difficult for IPv6-in-IPv4 tunnels. (Basically, tunnels
need to strike a balance between passing large packets and avoiding
excessive fragmentation in the IPv4 network.)

A new draft entitled: "Path MTU Support for IPv6-in-IPv4 Tunnels"
is available that specifies a means for IPv6-in-IPv4 tunnels to more
fully participate in path MTU discovery. The mechanisms can be applied
to various IPv6-in-IPv4 tunneling schemes, including 6to4, isatap,
teredo, 6over4, and RFC 2893(bis). Comments on the document are welcome:

  http://www.ietf.org/internet-drafts/draft-templin-tunnelmtu-00.txt

Fred Templin
ftemplin@iprg.nokia.com