[db-wg] "AND NOT" in as-expression

Dear Aris,

On Wed, May 21, 2014 at 04:59:11PM +0200, Aris Lambrianidis wrote:
> On 14 May 2014, at 14:20 , Job Snijders <job at instituut.net> wrote:
> 
> My follow up question, which actually is indirectly related, is if
> anyone is willing to share an opinion, as to whether "OR" can/should
> be used implicitly in as-expressions, besides filter expressions. 
> 
> This currently seems to not be the case (the RIPE test database
> doesn't accept it) and I wonder whether I am interpreting the RFC
> incorrectly or if it's something that can be considered valid and
> thus, honored.

What Aris proposes is the following, instead of writing this:
    import: from AS-ANY except ( AS1 OR AS2 OR AS3 ) accept ANY

One can compress as following:
    import: from AS-ANY except ( AS1 AS2 AS3 ) accept ANY

In other words: when AS or AS-SETS are grouped together, an implicit OR
is inserted between the individual AS expressions. This is slightly
different compared to what one is allowed to do inside
filter-expressions.

However, I oppose this proposal for the following reasons:
    
    - this is NOT specified in any RFC (most specifically rfc2622)
    - allowing this type of syntax is merely syntactic sugar
    - this change is NOT backwards compatible with existing RPSL parsers
    - a simple workaround exists: use AS-SETS
        * better readability
        * easier to maintain in an automated fashion

Therefor, I recommend the following policy structure if one wants to
exclude a set of ASNs from a specific import or export statement:

    as-set: AS-EXCLUDED-ASNS
    members: AS1
    members: AS2
    members: AS3

    aut-num: xxx
    import: from AS-ANY except AS-EXCLUDED-ASNS accept ANY

Kind regards,

Job