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</head><body bgcolor="#FFFFFF" text="#000000">excuse me, i left an edit
out of my earlier proposal.<br>
<br>
Paul Vixie wrote:
<blockquote cite="mid:522FE050.3050203@redbarn.org" type="cite">
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<span style="font-family: Courier New,Courier,monospace;">i do not
think
that the definition of mtu is wrong. if i were going to update 6891-bis
(which is itself 2671-bis) the logic i would draft is:</span><br
style="font-family: Courier New,Courier,monospace;">
<br>
---<br>
<br style="font-family: Courier New,Courier,monospace;">
<span style="font-family: Courier New,Courier,monospace;"><br></span></blockquote>
<br>
"A DNS UDP responder shall, when transmitting a message which does not
include embedded cryptographic marks such as TSIG or DNSSEC signatures,
use an effective DNS message payload size which is calculated as
MIN(OFFERED, MIN(DISCOVERED, ESTIMATED) - OVERHEAD)) where OFFERED is
the EDNS BUFSIZE received from the initiator, and DISCOVERED is the path
MTU if known or else the outbound interface MTU, and ESTIMATED is
chosen as 576 for IPv4 or 1280 for IPv6 as the minimum guaranteed size
of an IP datagram, and OVERHEAD is chosen as 64 for IPv4 or 48 for IPv6
as the maximum likely size of the IP and UDP headers.<br>
<br>
This specification does not define a maximum for any future IP transport
protocol, and so both initiators and responders should be prepared to
receive messages as large as the 9 kilobyte ethernet jumbogram size in
preparation for future transport protocol development."<br>
<br>
<blockquote cite="mid:522FE050.3050203@redbarn.org" type="cite"><span
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<br>
---<br>
<br>
i'm trying to decide whether that "should" ought to be a "must". and, i
know the number is 9K not 64K, because of buffer memory considerations
on today's embedded servers.<br>
<br>
vixie</span></blockquote>
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