As to the efficiency of file transfer, yes, if the header overhead is of fixed size, carrying more payload will increase efficiency. ie, if the IPv6 header is 40 bytes and the TCP header is 20, and the IPv6 MTU is 1500 bytes, the maximum payload we can carry is 1440 bytes, or 96%, and being able to switch that to a 9180 byte IPv6 MTU would change the efficiency to 99.3% and reduce the interrupt load an the two hosts by a factor of about 9180/1500. Changing from 1280 to 1500 bytes, however, is a change from 95.3% to 96% efficiency, which seems relatively minor, and switching from 1280 to 1380 bytes of payload seems even more trivial.
The principal value of getting the pmtu right, it seems to me, is to first get an estimated pmtu that in fact works at all (downsize it from the negotiated MSS to a packet size that works regardless of what hiccups lie en route), and second to that, it would be really nice to minimize the interrupt load on the sending and receiving hosts in order to balance the goals of maximizing throughput and minimizing the impact on the hosts themselves. ie, if the sender and receiver are on 10/100 Ethernets and there is an IP/IP tunnel on the path, carrying a 1280 byte payload is better than carrying a 1440 byte payload because the former works and the latter doesn't, and it would be nice to be able to figure out that a 1380 byte payload would also work and be a .35% improvement in efficiency.
So, question (and yes, this is a question): are you chasing a problem I don't see? What is the objective here?
On Oct 5, 2005, at 9:16 AM, Templin, Fred L wrote:
Fred, Please see the following draft which documents operational issues relevant to v6ops and calls for a solution: http://www.ietf.org/internet-drafts/draft-templin-mtuassurance-00.txt Please note that this obsoletes a previos draft called: "Requirements for Link Adaptation over IP-in-IPv4 Tunnels". Fred fred.l.templin@boeing.com-----Original Message----- From: Templin, Fred L Sent: Friday, September 30, 2005 3:40 PM To: Fred Baker Cc: v6ops@ops.ietf.org Subject: Requirements for Link Adaptation over IP-in-IPv4 Tunnels (was RE: Link Adaptation for IPv6-in-IPv4 Tunnels) Fred - please see: http://www.ietf.org/internet-drafts/draft-templin-linkadapt-re qts-00.txt Fred fred.l.templin@boeing.com-----Original Message----- From: Fred Baker [mailto:fred@cisco.com] Sent: Friday, September 23, 2005 9:24 AM To: Templin, Fred L Cc: v6ops@ops.ietf.org Subject: Re: Link Adaptation for IPv6-in-IPv4 Tunnels Does it still propose a protocol or protocol change? I don't know offhand whether the charter of v6ops then precluded protocol work, and won't go into whether it was proper for[MECH] tobe done in v6ops. Given the present charter, I can treat it as a requirements document that may be asking for something likethe workyou are proposing. But my read of the document you pointed to is that it is still proposing an incompatible change (as in "unchanged equipment will not perform the function and once the message is segmented in this fashion it must be reassembled in this fashion. I think that has to be done in a WG chartered to do non-backward- compatible changes to IPv4. On Sep 23, 2005, at 9:04 AM, Templin, Fred L wrote:Can this work be contributed as an extension to [MECH]?