Re: (ngtrans) I-D ACTION:draft-ietf-ngtrans-mech-v2-01.txt

[Pekka Savola <pekkas@netcore.fi>]

On Fri, 8 Nov 2002 Internet-Drafts@ietf.org wrote:
> 	Title		: Basic Transition Mechanisms for IPv6 Hosts and Routers
> 	Author(s)	: E. Nordmark, R. Gilligan
> 	Filename	: draft-ietf-ngtrans-mech-v2-01.txt
> 	Pages		: 25
> 	Date		: 2002-11-7

Just two comments on this:

   This dynamic MTU determination is OPTIONAL.  However, if it is
   implemented it SHOULD have the behavior described in this document
   and the tunnel MTU MUST be not exceed 4400 bytes.  If it is not
   implemented instead the node MUST instead limit the size of the IPv6
   packets it tunnels to 1280 bytes i.e., treat the tunnel interface as
   having a fixed interface MTU of 1280 bytes.  An implementation MAY
   have a configuration knob which can be used to set a larger value of
   the tunnel MTU than 1280 bytes, but if so the default MUST be 1280
   bytes.

==>
1) does 'tunnel MTU MUST be not exceed 4400 bytes' only apply to the 
dynamic MTU determination part or also to "manual configuration" part?
(probably the latter, but it's a bit unclear.)

2) Why just 4400, not e.g. 4500? (Note: ATM/POS links usually have a
default MTU of 4470 bytes, so either 4470+20 or 4470-20 (depending on
which kind of encapsulation you believe is more useful) would be one
interesting compromise, I believe.)

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords