nanog mailing list archives

Re: IPv6 day and tunnels


From: Joe Maimon <jmaimon () ttec com>
Date: Mon, 04 Jun 2012 18:34:31 -0400



Owen DeLong wrote:


Fail.


What, exactly are you saying is a failure? The single word here even in context is
very ambiguous.

The failure is that even now, when tunnels are critical to transition, a proper solution that improves on the IPv4 problems does not exist

And if tunnels do become less prevalent there will be even less impetus than now to make things work better.



Today, most people cant even get IPv6 without tunnels.

Anyone can get IPv6 without a tunnel if they are willing to bring a circuit to the right place.

Today most people cant even get IPv6 without tunnels, or without paying excessively more for their internet connection, or without having their pool of vendors shrink dramatically, sometimes to the point of none.



Breaking PMTU-D is bad. People should stop doing so.

Blocking PTB messages is bad in IPv4 and worse in IPv6.

It has always been bad and people have not stopped doing it. And intentional blocking is not the sole cause of pmtud breaking.



If you have a useful alternative solution to propose, put it forth and let's discuss the merits.

PMTU-d probing, as recently standardizes seems a more likely solution. Having CPE capable of TCP mss adjustment on v6 is another one. Being able to fragment when you want to is another good one as well.



I hope not. I hope that IPv6 will cause people to actually re-evaluate their behavior WRT PMTU-D and correct the actual 
problem. Working PMTU-D allows not only 1500, but also 1280, and 9000 and>9000 octet datagrams to be possible and segments 
that support<1500 work almost as well as segments that support jumbo frames. Where jumbo frames offer an end-to-end 
advantage, that advantage can be realized. Where there is a segment with a 1280 MTU, that can also work with a relatively 
small performance penalty.

Where PMTU-D is broken, nothing works unless the MTU end-to-end happens to coincide with the smallest MTU.

For links that carry tunnels and clear traffic, life gets interesting if one of them is the one with the smallest MTU 
regardless of the MTU value chosen.

Owen


I dont share your optimism that it will go any better this time around than last. If it goes at all.

Joe


Current thread: