Hi Tom, Manav,

On Feb 2, 2011, at 6:53 AM, t.petch wrote:

> ----- Original Message -----
> From: "Bhatia, Manav (Manav)" <[email protected]>
> To: "Acee Lindem" <[email protected]>; "Sam Hartman" <[email protected]>
> Cc: <[email protected]>; <[email protected]>; <[email protected]>
> Sent: Wednesday, February 02, 2011 3:53 AM
> 
>> Hi Acee,
>> 
>>> While most modern routers have a clock with fine enough
>>> granularity that will never go backwards, it is typically
>>> not preserved across cold restarts.
>>> If one used a 64 bit sequence number (for the required precision)
>>> and had a relative clock that was never reset, it would fit the bill.
>> 
>> One could store this value in a non volatile memory so that its also 
>> preserved
> across cold rebootd but I don't this would be an acceptable solution. Or would
> it be?
> 
> SNMPv3 introduces a requirement for non-volatile memory in which to store
> snmpEngineID and snmpEngineBoots [RFC3411] in order to avoid the
> requirement for a real time clock.  I do not know how strictly this
> requirement is being implemented.

I don't think we can put a requirement on the underlying hardware platform to 
solve this replay problem. A non-decreasing clock tick value is normally 
available on router platforms (for many other reasons) but the hardware to 
preserve it indefinitely is not. If one must preserve it manually with 
software, it decreases the attractiveness of the clock tick as a 64 bit 
sequence number since it needs to be updated very frequently in order to 
provide the required granularity. 

Thanks,
Acee

> 
> Tom Petch
> 
> <snip>
> 
>> 
>> 
>> Cheers, Manav
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