Subject: [Manet-dt] SMF: Usage of IPv4 Identification field

From: Teco Boot <[email-masked]>
Date: Fri, 13 Apr 2007 11:36:03 +0200

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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From: Brian Adamson <[email-masked]>
Date: Fri, 20 Apr 2007 09:10:59 -0400

I don't think the rules have been well-followed by some, most or 
maybe any operating systems.  I think most (Win32, BSD, while Linux 
seems to exhibit bit different behaviors) simply increment the ID 
field for each packet sent regardless of the destination ... This 
probably results in compliance with RFC 791, but is increasingly 
problematic for multi-homed cases or when there is great disparity of 
transmission rate for different flows that end up taking different 
paths through the network.  I think it is quite likely if one has a 
high bandwidth interface and another lower bandwidth (and perhaps 
long delay such as cellular, SATCOM) interface that a flow on the 
high speed interface could wrap the 16-bit sequence space in parallel 
with some low duty cycle flow on the slow interface.

In the age of higher speeds and multi-homing, etc ... I think it is 
worthwhile to clarify that sequence space SHOULD be managed at least 
on a per <source:destination> tuple basis

I suppose the <protocol> could be added, but that doesn't typically 
have bearing on the path the data takes ... although I guess it could 
for forms of policy-based routing, etc ....

The main thing is that it would be nice for operating systems to have 
some consistent behavior here ... in lieu of this, we made a specific 
recommendation to support SMF needs.

I am curious as to what others think here ...

-- 
Brian
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Brian Adamson
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