[Idr] Re: I-D Action: draft-kao-idr-bitwise-ip-filters-00.txt

[Nat Kao <[e-mail]>]

Hi, Robert.

Firstly, many thanks for your interest in this draft!

On Wed, Feb 19, 2025 at 10:11 PM Robert Raszuk <[e-mail]> wrote:

> Hello Nat,
>
> Would you be so kind and describe why matching on selective bits of src or
> dst address in the packets is needed ?
>
> As opposed to matching on all bits from or to a given position in the
> address ?
>
> What is the application which benefits from selective bit matches ?
>
> The primary use case of these filters is to match 1/Nth fraction of the
traffic from or to a specific prefix, provided traffic is distributed
almost uniformly among different combinations of the log(N) least
significant bits.
This assumption holds in most cases in a carrier, so we can match (almost)
1/Nth fraction of traffic uniformly in both directions using the bitwise
filter that matches the prefix with a specific combination of log(N) LSBs
and then put the matched traffic to the same service instance.
Therefore, the bitwise matching filters allow us to symmetrically
distribute traffic almost uniformly between N service instances in only N
rules.
AFAIK we cannot match only log(N) least significant bits using the IPv4
filters defined in FSv2-basic-ip or RFC8955 since the filter defined is
<Prefix, Prefix-Length>.
We can match either log(N) least significant bits or the IPv6 Prefix using
the IPv6 filters defined in RFC8956, but not both.

On the other hand, traffic is usually distributed non-uniformly between
different prefixes.
If we're trying to load-balance with filters matching contiguous bits since
the (almost) uniform distribution assumption does not hold, we need to
monitor the traffic of each prefix we can match in real time to
load-balance traffic.
This approach adds complexity and management costs.


> Your draft describes the mechanics and encoding, but I can not find the
> use case and real network applications for such selective bit maching. The
> first two paragraphs in the Introduction section IMO do not glue well to
> the rest of the draft.
>
> Thanks for your comments.
I'll try to improve that in the next version.


> Many thx,
> Robert
>

Many Thanks!
Nat

>
> ---------- Forwarded message ---------
> From: <[e-mail]>
> Date: Wed, Feb 19, 2025 at 12:13 PM
> Subject: I-D Action: draft-kao-idr-bitwise-ip-filters-00.txt
> To: <[e-mail]>
>
>
> Internet-Draft draft-kao-idr-bitwise-ip-filters-00.txt is now available.
>
>    Title:   Bitwise IP Filters for BGP FlowSpec
>    Author:  Nat Kao
>    Name:    draft-kao-idr-bitwise-ip-filters-00.txt
>    Pages:   12
>    Dates:   2025-02-19
>
> Abstract:
>
>    This draft introduces the bitwise matching filters for source or
>    destination IPv4/IPv6 address fields.  These filters enhance the
>    functionalities of the BGP Flow Specification framework and aid
>    scenarios involving symmetric traffic load balancing.
>
> The IETF datatracker status page for this Internet-Draft is:
> https://datatracker.ietf.org/doc/draft-kao-idr-bitwise-ip-filters/
>
> There is also an HTML version available at:
> https://www.ietf.org/archive/id/draft-kao-idr-bitwise-ip-filters-00.html
>
> Internet-Drafts are also available by rsync at:
> rsync.ietf.org::internet-drafts
>
>
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