Re: [IPFIX] Hash-based filtering config parameters

[Benoit Claise <bclaise at cisco.com>]

Gerhard,

> Hi Tanja, Benoit, all,
>
> I have two questions regarding the configuration of hash-based filtering.
>
> 1) Are IP header fields/bits fixed or configurable?
>
> RFC 5475, Section 7.2 says:
> http://tools.ietf.org/html/rfc5475#section-7.2
>
>    Case hashing:
>       - Hash Domain (input bits from packet)
>            - <Header type = IPv4>
>            - <Input bit specification, header part>
>            - <Header type =  IPv6>
>            - <Input bit specification, header part>
>            - <payload byte number N>
>            - <Input bit specification, payload part>
>
> => header bits seems to be configurable
>
>
> RFC 5476, Section 6.5.2.6 says:
> http://tools.ietf.org/html/rfc5476#section-6.5.2.6
>
>    In Hash-based Selection, a Hash Function is run on IPv4 traffic.  The
>    following fields MUST be used as input to that Hash Function:
>
>       - IP identification field
>
>       - Flags field
>
>       - Fragment offset
>
>       - Source IP address
>
>       - Destination IP address
>
>       - A number of bytes from the IP payload.  The number of bytes and
>         starting offset MUST be configurable if the Hash Function
>         supports it.
>
> => header fields seems to be fixed.
I would be tempted to believe the protocol. So RFC5476.

I'll let Tanja or Nick answer the question below.

Regards, Benoit.
> 2) Is the output range of the hash function a configuration parameter 
> or just an invariant property of the hash function itself?
> If yes, should it be configured as min and max or as length and bitmask?
>
> RFC 5475, Section 7.2 says:
> http://tools.ietf.org/html/rfc5475#section-7.2
>
>       - Hash Function
>            - Hash Function name
>            - Length of input key (eliminate 0x bytes)
>            - Output value (length M and bitmask)
>            - Hash Selection Range, as a list of non-overlapping
>              intervals [start value, end value] where value is in
>              [0,2^M-1]
>            - Additional parameters are dependent on specific Hash
>              Function (e.g., hash input bits (seed))
>
> => output value length and bitmask seem to correspond to the output 
> range defined by hashOutputRangeMin and hashOutputRangeMax
>
> Thanks,
> Gerhard