-----Original Message----- From: Masataka Ohta [mailto:mohta@necom830.hpcl.titech.ac.jp] Sent: Tuesday, June 19, 2012 6:10 AM To: Templin, Fred L Cc: Owen DeLong; nanog@nanog.org Subject: Re: IPv6 day and tunnels
Templin, Fred L wrote:
Not necessarily, as IPv4 can take care of itself and IPv6 is hopeless.
IPv4 can take care of it how - with broken PMTUD or
As you know, RFC1191 style PMTUD is broken both for IPv4 and IPv6.
Unfortunately, there is evidence that this is the case.
with broken fragmentation/reassembly?
Fragmentation is fine, especially with RFC4821 style PMTUD, even though RFC4821 tries to make people believe it is broken, because accidental ID match is negligibly rare even with IPv4.
The 16-bit IP ID, plus the 120sec MSL, limits the rate for fragmentable packets to 6.4Mbps for a 1500 MTU. Exceeding this rate leads to the possibility of fragment misassociations (RFC4963). This would not be a problem if there were some stronger integrity check than just the Internet checksum, but with the current system we don't have that.
And, you won't get any argument from me that IPv6 has been stuck for years for good reasons - but MTU failures can soon be taken off the list.
Now, it's time for you to return v6-ops to defend your draft from Joe Touch.
Note that there is no point for IPv6 forbid fragmentation by intermediate routers.
I wasn't there when the decision was made, but based on my findings I don't disagree. Fred fred.l.templin@boeing.com
Masataka Ohta