bgp4-17 5.1.3 NEXT_HOP attribute determination

["Tom Petch" <[e-mail]>]

I think that there is a problem with logic and terminology
in the determination of NEXT_HOP.  There are four cases
listed,
- a form of "third party" NEXT_HOP attribute
- a second form of "third party" NEXT_HOP attribute
- "first party" NEXT_HOP attribute
- by default
and respectively the BGP speaker
- can use
- can use
- may use
- should use
which seems inconsistent; I would prefer SHOULD.

But logically, the first party (common subnet) overlaps the
two third parties (common subnet with IBGP or locally
originated and common subnet with EBGP) which obviates
SHOULD.  And what does locally originated actually mean?
Presumably IGP and static except that the subsequent use of
internal router does not quite match that.

I wonder if it would be clearer if the focus was on the
common subnet rather than where the route came from.  Can eg
the third party cases be combined as

'if the external peer X shares a common subnet with the
immediate next hop that the BGP speaker itself has installed
in its routing table for this route, then the speaker SHOULD
use this immediate next hop in the NEXT_HOP attribute'

Tom Petch, Network Consultant
[e-mail]