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

[Brian Adamson <[e-mail]>]

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"


At 8:58:02 AM -0700 4/27/07, Charles E. Perkins wrote:

>Hello Teco,
>
>>ext Teco Boot wrote:
>>If memory is really cheap and memory lookups can be performed faster than
>>hash calculations, the DPD code could use packet header lookup instead of
>>hash lookup. Functionality is the same.
>Check.
>>Both mechanisms rely on unique
>>packet headers (say 1st 64 bytes or defined fields).
>The defined fields could include some amount of payload.
>>
>>That is what should be
>>specified in the standard. Which method is used for verifying duplicates is
>>an implementation issue.
>I think for IPv6 has also to specify which hash function
>to use.  For IPv4 I am hoping we do not need a hash function or any 
>DPD header.
>Regards,
>Charlie P.


-- 
Brian
__________________________________
Brian Adamson
<mailto:[e-mail]>

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