netdev - Re: UDP path MTU discovery

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Message-ID: <1269898152.1958.86.camel@edumazet-laptop>
Date:	Mon, 29 Mar 2010 23:29:12 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	"Edgar E. Iglesias" <edgar.iglesias@...il.com>,
	Andi Kleen <andi@...stfloor.org>, Glen Turner <gdt@....id.au>,
	netdev@...r.kernel.org
Subject: Re: UDP path MTU discovery

Le lundi 29 mars 2010 à 14:01 -0700, Rick Jones a écrit :

> I would get the alphabet soup completely garbled, but the DNS folks are talking 
> about EDNS (?) message sizes upwards of 4096 bytes - encryption/authentication 
> and other angels being asked to dance on the head of the DNS pin are asking for 
> more and more space in the messages.
> 
> So, someone will have to blink somewhere - either DNS will have to go TCP and 
> *possibly* take RTT hits there depending on various patch streams, or the IEEE 
> will have to sanction jumbo frames and people deploy them widely, or it will 
> have to become feasible to actually do the occasional IPv6 datagram 
> fragmentation and get a timely retransmission out of a UDP application on a PMTU 
> hit.
> 

1) 4096 bytes UDP messages... well...
2) Using regular TCP for DNS servers... well...

I believe some guys were pushing TCPCT (Cookie Transactions) for this
case ( http://tools.ietf.org/html/draft-simpson-tcpct-00.html )

(That is, using an enhanced TCP for long DNS queries... but not only for
DNS...)



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