RINA - scott whaps at the nanog hornets nest :-)

George Bonser gbonser at seven.com
Mon Nov 8 10:53:47 CST 2010

> Even if larger MTUen are interesting (but most of the time not worth
> the work) the sole reason I like SDH  as my WAN technology is the
> presence of signalling -- so that both ends of a link are aware of its
> status near-instantly (via protocol parts like RDI etc). In GE it is
> legal to not receive any packets, which means that "oblivious" is a
> possible state for such a connection. With associated routing
> implications.

I wasn't talking about changing anything at any of the edges.  The idea was just to get the "middle" portion of the internet, the peering points to a place that would support frames larger than 1500.  It is practically impossible for anyone to send such a packet off-net until that happens.

There was nothing that said everyone should change to a higher MTU.  I was saying that there are cases where it can be useful for certain types of transfers but the state of today's internet is that you can't do it even if you want to except by special arrangement.  Considering the state of today's modern hardware, there isn't a technical reason why those points can't be set to handle larger packets should one come along.  That's all.  I wasn't suggesting everyone set their home system for a larger MTU, I was suggesting that the peering points be able to handle them should one pass through.

Now I agree, on an existing exchange having a "flag day" for everyone to change might not be worthwhile but on a new exchange where you have a green field, there is no reason to limit the MTU at that point to 1500.  Having a larger MTU in the middle of the path does not introduce PMTUD issues. PMTUD issues are introduced by having a smaller MTU somewhere in the middle of the path.  The conversation was quickly dragged into areas other than what the suggestion was about.

What was interesting was the email I got from people who need to move a lot of science and engineering data on a daily basis who said their networking people didn't "get it" either and it is causing them problems.  Not everyone is going to need to use large frames.  But people who do need them can't use them and there really isn't a technical reason for that.  That specific portion of the Internet, the peering points between networks, carries traffic from all sorts of users, not just people at home with their twitter app open.  Enabling the passage of larger packets doesn't mean advocating that everyone use them or changing anyone's customer edge configuration.

It wouldn't change anyone's routing, wouldn't impact anyone's PMTUD problems.  I don't believe that is "kooky". A lot of other people have been calling for the same thing for quite some time. But making a network "jumbo clean" doesn't do a lot of good if the peering points are the bottleneck. That's all.  Removing that bottleneck is all that the suggestion was about.

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