Subject: Re: [nemo] NEMO for IPv4

From: Chan-Wah NG <[email-masked]>
Date: Thu, 10 Nov 2005 09:03:09 +0800

Hello, 

I must first admit that I have not read the entire draft, this is just a
quick comment after hearing Alex's presentation today.

On Tue, 2005-10-18 at 09:54 +0200, Alexandru Petrescu wrote:
> We've just submitted draft-leung-nemov4-base-00.txt and until it shows
> on the rfc-editor site it could be found at:
> 
> http://www.mobilenetworks.org/nemo/drafts/draft-leung-nemov4-base-00.txt
> 
> and attached (we have missed the deadline by a few hours.)
> 
> Knowing the past list interest in IPv4 NEMO and existing IPv4 NEMO-like
> implementations we think we need interoperability.  The 23 pages of text
> propose two extensions to Registration Request and Reply to carry Mobile
> Network Prefixes, the respective MR and HA behaviours and IANA numbers.
> 
> We would like to target the draft as a WG document at some point.
> 
> We would like to obtain feedback on the document from the WG members on
> the mailing list prior to discussion in Vancouver.
> 

.....

>       0               1               2               3
>       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      |     Type      |    Length     |   Sub-Type    |      Code     |
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      | Prefix Length |                      Prefix
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>                      |
>      +-+-+-+-+-+-+-+-+
> 

I am just wondering what is the reason behind starting the prefix field
at the 5th byte instea dof the normal convention of starting a field at
its proper byte-aligned boundary.  I know IPv4 does not have a strict
requirement for byte-boundary alignment like IPv6, so there is no need
to create empty reserved bits just for byte-alignment.  However, in this
case, a simple re-ordering of the Code / Prefix-Length / Prefix field
would achieve a natural byte alignment.  So I am wondering if there is a
technical reason why that is not done.  If there is no technical reason,
I would suggest the re-ordering of the fields.

/rgds
/cwng

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 09 Nov 2005 22:58:22 -0800

> I would suggest the re-ordering of the fields.

Right,

BAsically the order of fields in the message is something we've
discussed at length between authors.  What we wanted at some point was
to have them a little bit more aligned but we couldn't quite agree.

I am not sure what order you prefer.  Is the preferred order in your
oppinion like Code/Prefix/PrefixLen (instead of Code/PrefixLen/Prefix)
such as to have the Prefix itself on a 4-byte boundary?  If yes, that
sounds like a good idea to me.  If no other opposition we'll do just
that, sounds like a good idea:

      0               1               2               3
     |                            Prefix                             |
     | Prefix Length |
     +-+-+-+-+-+-+-+-+

Thanks,

Alex