From: Jun-ichiro itojun Hagino <[EMAIL PROTECTED]>
Subject: Re: ENDS0
> I don't understand why you say so. Please check the logic behind
> IPv4 DNS UDP payload length. It is set to 512, because minimum IPv4
> fragment reassembly size is 576. the mergin between 576 and 512
> (576 - 512 = 64) came from IPv4 header, UDP header and possible IPv4
> options and extension headers.
Sorry, itojun. I think you misunderstand this.
To my best knowledge:
512 is just defined by RFC 1034 as UDP payload size(ie. buffer size).
The maximum IPv4 hdr (60) + UDP hdr (8) + DNS UDP payload size (512)
equals to 580, which exceeds 576.
See Section 3.1, RFC 791:
The number 576 is selected to allow a reasonable sized data block to
be transmitted in addition to the required header information. For
example, this size allows a data block of 512 octets plus 64 header
octets to fit in a datagram. The maximal internet header is 60
octets, and a typical internet header is 20 octets, allowing a
margin for headers of higher level protocols.
You can see magic number 64, which I think is meaningless, at least
these days.
# 4 bytes are missing...
--Kazu
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