Subject: [manet] RE: SMF: Usage of IPv4 Identification field

From: Teco Boot <[email-masked]>
Date: Fri, 20 Apr 2007 10:02:52 +0200

I have a remark on using IPv4 DPD and support for fragmentation. I think it
is not that difficult to support fragmentation, we only have to extent the
DPD filter for Fragment Offset (and Protocol, to be compliant with RFC791).
Incorporating the Flags field (e.g. more fragments) is not needed but not
harmful either.

The DPD filter should check on Source Address, Destination Address,
Protocol, Identification and Fragment Offset. Out of RFC791; header fields
not used by DPD are blanked:
                                
    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 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       |       |               |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Identification        |     |      Fragment Offset    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |    Protocol   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Source Address                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Destination Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                               |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Example Internet Datagram Header

                               Figure 4.

IMHO updating DPD to RFC791 is important. Also for using it as remedy for
unicast routing loops as I suggested before.

Cheers, Teco

> -----Original Message-----
> From: Teco Boot [mailto:[email-masked]]
> Sent: vrijdag 13 april 2007 11:36
> To: [email-masked]'
> Subject: SMF: Usage of IPv4 Identification field
> 
> The SMF ID deviates from RFC791 for the Identification field.
> 
> 791: "The originating protocol module of an internet datagram sets the
> identification field to a value that must be unique for that source-
> destination pair and protocol"
> 
> SMF: "In the case that resequencing is deemed necessary, it is RECOMMENDED
> that sequence numbering be applied such that a different sequence number
> space per <sourceAddress::destinationAddress> duple be used"
> 
> The difference is the protocol field. I see two options, modify SMF or add
> text clarifying the deviation and analyze for consequences. Or are the
> rules for Identification changed since 791?
> 
> Teco

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