Hi,
>From: Iljitsch van Beijnum <[EMAIL PROTECTED]>
>Date: Thu, 21 Jul 2005 10:19:56 +0200
> My common sense tells me that the authors of RFC 2464 didn't consider
> the case where the MTU would legitimately be larger than 1500 bytes.
> They did consider the case where router advertisements contain an MTU
> that is apparently incorrect, because it's larger than the standard
> allows.
I think so. When RFC2464 was issued, GbE and Jumbo Frames were not so
deloied, the authors must have believed that the maximum MTU of
ehternet is 1500. It was reasonable at the time.
> So in my opinion, an implementation that supports jumboframes should
> use the interface MTU for IPv6 by default, and reduce this MTU for
> IPv6 to the one in an MTU option in router advertisements, when such
> an option is received.
Yes, your idea is a realistic, and also equal to almost current
implementations, I think.
BTW, suppose following netowrk.
Internet
|
ROUTER
|
| 100BASE-TX / MTU=1500
|
GbE-SWITCH
| |
| | 1000BASE-T / MTU=9018
| |
HOST1 HOST2
HOST1, HOST2 and GbE-SWITCH support 1000BASE-T and Jumbo Frames, but
ROUTER has only 100BASE-TX interfaces and doesn't support Jumbo
Frames. In this network, ROUTER will send RA. If the MTU option,
which value is 1500, is included in RA, HOST1 and HOST2 will accept
it, and are disabled Jumbo Frames. So, if we want to use Jumbo
Frambes between HOSTs, (1) HOSTs must neglect MTU option, (2) ROUTER
must send RA without MTU option, (3) or ROUTER must send RA with MTU
option which value is 9018, illegal MTU for ROUTER itself.
(2) RA without MTU option is always valid. But (1) neglect MTU
option, or (3) MTU option with illegal value for sender itself, are
acceptable?
Ryota Hirose
Yamaha Corporation
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