Re: Transport requirements for DNS-like protocols
Dave Crocker <dhc2@dcrocker.net> Sun, 30 June 2002 04:25 UTC
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Date: Sat, 29 Jun 2002 21:25:05 -0700
From: Dave Crocker <dhc2@dcrocker.net>
Subject: Re: Transport requirements for DNS-like protocols
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To: Michael Mealling <michael@neonym.net>
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At 11:04 PM 6/29/2002 -0400, Michael Mealling wrote: >The proposal I've been toying with was to limit the number of packets >in the train to some number equating to *small*. Anything above that >is responded to with a "I'm sorry but the response is on the order of >a file stransfer instead of a simple response so please requery via TCP". interesting idea. >But sans some hard network testing across variously connected parts of >the network I have no idea how to come up with that number. worse, today's statistics don't necessarily predict tomorrow's. >Yes. The fact that fragmentation is the exception rather than the rule >means that the context switching required during the probable situation >that the router is 'stressed' suggests that the large UDP packet solution >is relying on the network feature most likely to fail instead of most >likely to succeed. Also it is bad in the receiving host. With IP fragmentation, the fragment is held down in the IP layer, consuming a network buffer. > We have good evidence that UDP packets smaller than >512 bytes succeed at a high rate. IMHO, we should optimize to what will >succeed rather than what is an error correction. exactly. for all of the processing efficiencies of larger packets, quick DNS-like transactions might be the place to bias towards smaller chunks. > > >That is, even in the > > >absence of PMTU discovery, there is still a chance that a larger than > > >minimum IP packet might still make it through the net unfragmented. > > > > But the fact that it might not is the problem. > >Correct. Its the recovery from the dropped fragments that causes additional >network impact and increased delay due to timeouts for the user. With a dropped fragment, the entire IP datagram must be resent. An application-level, selective-retransmission scheme does not incur that. Still, there is the minor issue of retaining state in the server application. > > Perhaps the way to avoid this mistake is to make DNS use a transport > > protocol that does not rely on the size of the underlying packets. The > > easiest way to do this is a thin layer ON TOP of UDP, that strings them > > together. > >Beyond a simple sequence number and possible checksum in the first octet, >would anything else be needed. The only thing I can think of is >some additional octet in the first packet indicating the total number >of packets sent. Sounds about right. The issue is not designing such a mechanism. It's the impact on the servers that I would guess to be the major issue. > > However to add selective retransmission requires that the server > 'assemble' > > the DNS query and acknowledge its parts selectively. Hence the server > > becomes statement. > >And increases server demands to the point that a cost of a truly reliable >connect becomes the optimal solution, when in truth it ends up being >overkill. Not if we are faced with a true requirement for larger application data units, as it seems we are (and, frankly, have been for a number of years.) The debate is how to provide those larger transaction units, not whether. d/ ---------- Dave Crocker <mailto:dave@tribalwise.com> TribalWise, Inc. <http://www.tribalwise.com> tel +1.408.246.8253; fax +1.408.850.1850
- Re: Transport requirements for DNS-like protocols John C Klensin
- RE: Transport requirements for DNS-like protocols John C Klensin
- Re: Transport requirements for DNS-like protocols Dave Crocker
- Re: Transport requirements for DNS-like protocols Michael Mealling
- Re: Transport requirements for DNS-like protocols Eric Brunner-Williams in Portland Maine
- Re: Transport requirements for DNS-like protocols Dave Crocker
- RE: Transport requirements for DNS-like protocols Patrik Fältström
- Re: Transport requirements for DNS-like protocols Rob Austein
- Re: Transport requirements for DNS-like protocols Eric Brunner-Williams in Portland Maine
- RE: Transport requirements for DNS-like protocols John C Klensin
- RE: Transport requirements for DNS-like protocols Nicolas Popp
- Re: Transport requirements for DNS-like protocols Patrik Fältström
- Re: Transport requirements for DNS-like protocols John C Klensin
- Re: Transport requirements for DNS-like protocols Patrik Fältström
- Re: Transport requirements for DNS-like protocols Eric Brunner-Williams in Portland Maine
- Re: Transport requirements for DNS-like protocols John C Klensin
- Re: Transport requirements for DNS-like protocols Eric Brunner-Williams in Portland Maine
- Re: Transport requirements for DNS-like protocols Michael Mealling
- Re: Transport requirements for DNS-like protocols Patrik Fältström
- Re: Transport requirements for DNS-like protocols Michael Mealling
- Re: Transport requirements for DNS-like protocols John C Klensin
- Re: Transport requirements for DNS-like protocols Michael Mealling
- Re: Transport requirements for DNS-like protocols John C Klensin
- Re: Transport requirements for DNS-like protocols Michael Mealling
- Re: Transport requirements for DNS-like protocols Patrik Fältström
- Transport requirements for DNS-like protocols Rob Austein
- RE: Transport requirements for DNS-like protocols Patrik Fältström
- RE: Transport requirements for DNS-like protocols John C Klensin
- RE: Transport requirements for DNS-like protocols Patrik Fältström