[db-wg] Proxy proposal large communities

On Mon, Nov 13, 2017 at 01:11:46AM +1030, Mark Prior wrote:
> On 13/11/17 00:58, Job Snijders wrote:
> > On Sun, 12 Nov 2017 at 15:17, Mark Prior via db-wg <db-wg at ripe.net
> > <mailto:db-wg at ripe.net>> wrote:
> > 
> > Wouldn't it be better to just change the definition of community in
> > the RPSL dictionary so that a community of <digit>+ ":" <digit>+ ":"
> > <digit>+ is valid and then have the tools either barf if they don't
> > understand or do "the right thing"? That would seem more consistent
> > with the current scheme where a community can either be an integer
> > or <digit>+ ":" <digit>+.
> > 
> > That goes against the documented recommendations on how to upgrade
> > RPSL. 
> 
> That's not my reading of RFC 2622 section 10.1. My suggestions seems
> consistent with the change to route damping mentioned in that section.

Section 10.1 says:

    "We recommend updating the RPSL dictionary to include appropriate
    rp-attribute and protocol definitions as new path attributes or
    router features are introduced."

Large BGP Communities [RFC 8092] are a new path attribute, so a new
rp-attribute should be used. Old parsers will ignore the new (to them
unknown) rp-attributes.

Furthermore the section states:

    "When changing the dictionary, full compatibility should be
    maintained."

When an 'old' parser encounters the following:

	mp-export: afi ipv6.unicast to AS13105 announce AS-RCNET-V6 AND NOT community.contains(21414:0:570)

It'll be seen as a syntax error, because the parameters to 'community'
are already defined, and "21414:0:570" doesn't meet that definition, so
that is not backwards compatible.
    
    typedef:
      community_elm union
      integer[1, 4294967200],
      enum[internet, no_export, no_advertise],
      list[2:2] of integer[0, 65535]
    typedef:
      list of community_elm

Section 10 of RFC 2622 should've used a different phrasing, instead of
talking about "updating the dictionary" it could've been more explicit
and stated "adding or removing rp-attributes from the dictionary".

Changing existing entries of the dictionary is hard. Section 10.4 sums
it up.

Kind regards,

Job