Re: [Manet-dt] Re: [manet] Need for DPD header (SMF document discussion) - ValidReason for Tagger ID

Brian Adamson <adamson@itd.nrl.navy.mil> Wed, 02 May 2007 20:44 UTC

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Date: Wed, 02 May 2007 16:44:04 -0400
To: "Charles E. Perkins" <charles.perkins@nokia.com>
From: Brian Adamson <adamson@itd.nrl.navy.mil>
Subject: Re: [Manet-dt] Re: [manet] Need for DPD header (SMF document discussion) - ValidReason for Tagger ID
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Charlie,

Whatever 'C' code you have we might be able to work with in some way. 
Better yet if you had a full-up forwarding engine we could use ... 
But we can do a little work here and I'm not afraid of bugs (I do a 
nice job of cultivating my own herd of those), etc.  I just would 
like to compare the space/complexity needed with each approach.

Wr2 to a simpler SMF DPD option, it's hard to do much simpler for 
IPv6 because of the multiple of 8 octets sizing that IPv6 option 
headers require ... yes, _some_ savings might be garnered under 
certain conditions when other options were also present, but the 
current SMF DPD options adds the minimum possible to an IPv6 its the 
only option added.



At 11:09 AM -0700 5/2/07, Charles E. Perkins wrote:
>Hello Brian,
>
>I have some 'C' code that I have adapted
>from other sources, and if you like I can
>send it to you.  Of course you have to
>promise not to be too disappointed if you
>find bugs, and please send any improvements
>back to me so I can reincorporate it into
>the code I have.  It isn't very much, and
>at least half of it was grabbed from existing
>code on the net (including RFC 1321, which
>excuses me from any wrongdoing about the
>formatting and stylistic issues).
>
>Ian suggested that there was agreement
>that the hashing was effective, and asked
>whether the other features of the DPD
>header were sufficient to warrant its use
>(in favor of hashing).
>
>I do _not_ suggest that applications take
>any responsibility for generating unique
>hash codes.  To summarize, I prefer if we
>make hashing "good enough", and then use
>the DPD header for the rare cases where
>the hash function fails to distinguish different
>flooded packets.  Used in this way, the
>DPD header could be a lot simpler.
>
>Regards,
>Charlie P.
>
>
>ext Brian Adamson wrote:
>>Charlie, Teco
>>
>>Do either you have implementations of hash or packet lookup 
>>approaches that we could try or incorporate into our "nrlsmf" 
>>implementation so we can look at the performance/computation 
>>complexity/space trade-offs more?
>>
>>I am concerned that complexity/space needed for these approaches 
>>may be prohibitive for some applications (and I am curious about 
>>the performance of the hash to not have false duplicates) compared 
>>to our current approach.  But I am not opposed to allowing for both 
>>approaches to be specified or options if appropriate.
>>
>>The other issue is that imposing a requirement on applications to 
>>generate unique packet payloads (while probably generally good 
>>practice) may be inappropriate for a network layer specification?
>>
>>Also, Teco had mentioned in an earlier email he was concerned that 
>>"a bit table
>>with packets received with offsets to a sequence number base (as often used
>>in IPsec replay detection code) is not usable" ... I am not sure if 
>>that comment was limited to the fragmentation issue that was being 
>>discussed or with regard to SMF DPD in general?  We have used this 
>>sort of approach successfully with IPv4 and IPv6 in fairly 
>>extensive laboratory and field tests for the past few years 
>>(although not with any fragmentation).  However, it is not strictly 
>>a a packet bit mask, a timer is used to detect/prune stale packet 
>>flows as well, and there is a strategy involved to allow for the 
>>bitmask to provide a sort of "sliding window"
>>_______________________________________________
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>>


-- 
Brian
__________________________________
Brian Adamson
<mailto:adamson@itd.nrl.navy.mil>


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