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Re: [dhcwg] WGLC for draft-ietf-dhc-sedhcpv6-02 - Respond by May 18

神明達哉 <jinmei@wide.ad.jp> Wed, 07 May 2014 20:26 UTC

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Date: Wed, 07 May 2014 13:25:58 -0700
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From: 神明達哉 <jinmei@wide.ad.jp>
To: Ted Lemon <ted.lemon@nominum.com>
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Cc: dhcwg <dhcwg@ietf.org>, Bernie Volz <volz@cisco.com>, Ralph Droms <rdroms.ietf@gmail.com>
Subject: Re: [dhcwg] WGLC for draft-ietf-dhc-sedhcpv6-02 - Respond by May 18
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At Wed, 7 May 2014 14:07:58 -0500,
Ted Lemon <ted.lemon@nominum.com> wrote:

> I think this option is not only unnecessary, but harmful, when used with DHCP, because it sets the maximum DHCP message size to 1280

why?  This option just makes the message (however big it is) to be
fragmented at 1280 bytes.

> The reason why you might want to enable this option for DNS is that
> you really care about latency on DNS queries, and waiting for PMTU
> discovery increases latency.   No such problem exists for DHCP

Hmm, I thought many kernel implementations don't trust an incoming too
big message unless it has a corresponding connected socket to avoid
resource exhaustion DoS and PMTU discovery didn't work well for non
connected sockets (often the case for UDP applications).  But more
recent implementations seem to be smarter than that, allowing such
messages with some limitation.  So, in the end, it seems I was wrong:
as you said this option won't be necessary for DHCPv6 (still not sure
if it's "harmful" though as stated above, but that's not important at
this point).

--
JINMEI, Tatuya

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