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

["Charles E. Perkins" <[e-mail]>]

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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